Relaxation Of Corpus Cavernosum Research Articles

Nitric Oxide Resistance in Priapism Associated with Sickle Cell Disease: Mechanisms, Therapeutic Challenges, and Future Directions.

Patients with sickle cell disease (SCD) display priapism, a prolonged penile erection in the absence of sexual arousal. The current pharmacological treatments for SCD-associated priapism are limited and focused on acute interventions rather than prevention. Thus, there is an urgent need for new drug targets and preventive pharmacological therapies for this condition. This review focuses on the molecular mechanisms linked to the dysfunction of the NO-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) pathway implicated in SCD-associated priapism. In murine models of SCD, reduced NO-cGMP bioavailability in the corpus cavernosum is associated with elevated plasma hemoglobin levels, increased ROS levels that inactive NO, and testosterone deficiency that leads to eNOS downregulation. We discuss the consequences of the reduced cGMP-dependent PDE5 activity in response to these molecular changes, highlighting it as the primary pathophysiological mechanism leading to excessive corpus cavernosum relaxation, culminating in priapism. We also further discuss the impact of intravascular hemolysis on therapeutic approaches, present current pharmacological strategies targeting the NO-cGMP-PDE5 pathway in the penis, and identify potential pharmacological targets for future priapism therapies. In men with SCD and priapism, PDE5 inhibitor therapy and testosterone replacement have shown promising results. Recent preclinical research reported the beneficial effect of treatment with haptoglobin and NO donors. Significant strides have been made in understanding the pathophysiology of SCD-associated priapism. Significance Statement This review discusses the molecular changes that reduce NO-cGMP bioavailability in the penis in SCD and highlights pharmacological targets and therapeutic strategies for the treatment of priapism, including PDE5 inhibitors, hormonal modulators, NO donors, soluble guanylate cyclase stimulators, haptoglobin, hemopexin, and antioxidants.

Heme-induced corpus cavernosum relaxation and its implications for priapism in sickle cell disease: a mechanistic insight.

Patients with sickle cell disease (SCD) experience intravascular hemolysis, leading to elevated plasma heme levels. This phenomenon has been associated with increased priapism in men with SCD. The heme group can be metabolized by heme oxygenase (HO), generating carbon monoxide (CO), which is known to promote smooth muscle relaxation via soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP). However, the effects of heme on the relaxation responses of corpus cavernosum (CC) have not been investigated. To evaluate the functional and biochemical effects of the heme group on mouse CC smooth muscle in vitro. Male C57BL/6 mice were used. CC tissues were mounted in organ baths. Measurement of cGMP in mice CC was evaluated. The cumulative addition of heme concentrations promoted the relaxation of CC. HO inhibitor (1J, 100μM) or sGC inhibitor (ODQ, 10μM) blocked the relaxing effect of the heme group. Pre-incubation of CC with heme (100μM) enhanced relaxation induced by acetylcholine, sodium nitroprusside, and nitrergic relaxation (electrical field stimulation), which was abolished by 1J or ODQ. The heme group increased the cGMP production in CC, which was abolished by 1J or ODQ. cGMP levels were significantly higher in CC treated with heme, and pre-incubation with compound 1J or ODQ abolished the effect of heme in raising cGMP levels. The HO-CO-sGC-cGMP pathway appears to play a crucial role in promoting CC relaxation. Our study provides novel insight into the role of group heme in CC relaxation and its potential contribution to priapism in SCD. Heme may serve as a pharmacological target for new therapies to prevent priapism.

6-Nitrodopamine is an endogenous mediator of the rabbit corpus cavernosum relaxation.

6-Nitrodopamine (6-ND) is a novel endogenous catecholamine that has a potent relaxant action on vascular smooth muscle in vitro. To evaluate the basal release of 6-ND and noradrenaline from rabbit-isolated corpus cavernosum (RbCC) and its relaxing action on this tissue. Rabbit corpus cavernosa were dissected and suspended in a 5-mL organ bath containing oxygenated Krebs-Henseleit's solution. 6-ND and noradrenaline release was quantified by liquid chromatography coupled to tandem mass spectrometry. The relaxant activity of 6-ND was assessed in RbCC strips pre-contracted with endothelin-1 (10nM). Rabbit corpus cavernosum presented basal release of both 6-ND (2.9±0.8ng/mL, n=12) and noradrenaline (1.7±1.3ng/mL, n=12). The 6-ND release was reduced by pre-treatment with Nω -nitro-l-arginine methyl ester (l-NAME) (100 µM), whereas that of noradrenaline was unaffected. Tetrodotoxin (TTX, 1 µM) abolished the noradrenaline release but had no effect on 6-ND release, indicating a non-neurogenic origin for 6-ND. 6-ND and the selective dopamine D2 -agonist L-741,626 caused concentration-dependent RbCC relaxations (pEC50 of 11±0.15 and 11.15±0.28, respectively). Pre-treatment with either l-NAME or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-on (ODQ) (100 µM) caused a rightward shift of the concentration-response curve to 6-ND, without affecting the L-741,626 responses. In TTX (100nM)-pre-treated preparations, neither l-NAME nor ODQ shifted the 6-ND concentration-response curve. Dopamine, noradrenaline, and adrenaline caused concentration-dependent RbCC contractions. Pre-incubation with 6-ND concentration-dependently inhibited the dopamine-induced contractions, without affecting those induced by either noradrenaline or adrenaline. 6-Nitrodopamine is the most potent endogenous relaxant agent in RbCC ever described and represents a novel mechanism by which NO causes corpus cavernosum smooth muscle relaxation. The finding that 6-ND acts as a truly selective dopamine D2 -receptor antagonist indicates that the balance of dopamine and 6-ND release/synthesis may be the main mechanism that modulates corpus cavernosum smooth muscle tonus in vivo.

Hydroxyurea does not reverse functional alterations of the nitric oxide-cGMP pathway associated with priapism phenotype in corpus cavernosum from sickle cell mouse.

Sickle cell disease (SCD) is a genetic disorder that has been associated with priapism. The role of hydroxyurea, a common SCD therapy, in influencing the nitric oxide (NO)-cGMP pathway and its effect on priapism is unclear. To investigate the effect of hydroxyurea treatment on smooth muscle relaxation of corpus cavernosum induced by stimulation of the NO-cGMP pathway in SCD transgenic mice and endothelial NO synthase gene-deficient (eNOS-/-) mice, which are used as model of priapism associated with the low bioavailability of endothelial NO. Four-month-old wild-type (WT, C57BL/6), SCD transgenic, and eNOS-/- male mice were treated with hydroxyurea (100 mg/Kg/day) or its vehicle (saline) daily for three weeks via intraperitoneal injections. Concentration-response curves for acetylcholine (ACh), sodium nitroprusside (SNP), and electrical field stimulation (EFS) were generated using strips of mice corpus cavernosum. The SCD mice demonstrated an amplified CC relaxation response triggered by ACh, EFS, and SNP. The corpus cavernosum relaxation responses to SNP and EFS were found to be heightened in the eNOS-/- group. However, the hydroxyurea treatment did not alter these escalated relaxation responses to ACh, EFS, and SNP in the corpus cavernosum of the SCD group, nor the relaxation responses to EFS and SNP in the eNOS-/- group. In conclusion, hydroxyurea is not effective in treating priapism associated with SCD. It is likely that excess plasma hemoglobin and reactive oxygen species, which are reported in SCD, are reacting with NO before it binds to GCs in the smooth muscle of the corpus cavernosum, thus preventing the restoration of baseline NO/cGMP levels. Furthermore, the downregulation of eNOS in the penis may impair the pharmacological action of hydroxyurea at the endothelial level in SCD mice. This study emphasize the urgency for exploring alternative therapeutic avenues for priapism in SCD that are not hindered by high plasma hemoglobin and ROS levels.

Comparative Study Between Behavior Therapy and Behavior Therapy Plus Mirabegron 50 mg in Sexually Active Men With Bothersome Overactive Bladder Symptoms - A Multicenter, Randomized Study.

We evaluated the therapeutic effects on overactive bladder (OAB) symptoms and sexual function of behavioral therapy with or without mirabegron in sexually active male patients with OAB. Mirabegron, a selective β3 adrenoceptor agonist for the treatment of OAB, has been shown to induce corpus cavernosum relaxation. In this 4-site, randomized controlled trial, 150 sexually active men with OAB were enrolled between June 2020 and May 2022. Participants were randomly allocated (1:2) into 2 treatment groups: (1) behavioral therapy alone (n = 50) and (2) a combination of mirabegron 50 mg daily and behavioral therapy (n = 100). The evaluation was based on the overactive bladder symptoms score (OABSS), the International Index of Erectile Function, the ejaculatory domain short form, the International Prostate Symptom Score, patient perception of bladder condition, quality of life, and urodynamic parameters. The therapeutic outcomes were assessed at baseline, 4 weeks, and 12 weeks. There were 65 patients (65%) in the combination subgroup and 36 patients in the behavioral therapy who completed all 12 weeks of treatment. Both groups had a statistically significant improvement in OABSS after 12 weeks of treatment. The combination therapy group achieved a statistically significant improvement in all 4 subscores of OABSS, however, the urinary frequency (P = 0.120) and urinary incontinence (P = 0.234) subscores in the behavioral therapy only group did not show a significant change. Additionally, the combination group had a significant improvement in functional bladder capacity, which was not seen in the behavioral therapy group. However, both groups did not have a significant change in erectile or ejaculatory function. Behavioral therapy combined with mirabegron had more significant impact on the improvement of OAB than behavior therapy alone. However, both groups did not have significant changes in erectile or ejaculatory function.

The bitter taste receptor (TAS2R) agonist denatonium promotes a strong relaxation of rat corpus cavernosum

Bitter taste receptors (TAS2R) are found in numerous extra-oral tissues, including smooth muscle (SM) cells in both vascular and visceral tissues. Upon activation, TAS2R stimulate the relaxation of the SM. Nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway is involved in penile erection, and type 5 phosphodiesterase (PDE5) inhibitors, a cGMP-specific hydrolase are used as first-line treatments for erectile dysfunction (ED). Nevertheless, PDE5 inhibitors are ineffective in a considerable number of patients, prompting research into alternative pharmacological targets for ED. Since TAS2R agonists regulate SM contractility, this study investigates the role of TAS2Rs in rat corpus cavernosum (CC). We performed immunohistochemistry to detect TAS2R10, isometric force recordings for TAS2R agonists denatonium and chloroquine, the slow-release H2S donor GYY 4137, the NO donor SNAP, the β-adrenoceptor agonist isoproterenol and electrical field stimulation (EFS), as well as measurement of endogenous hydrogen sulfide (H2S) production. The immunofluorescence staining indicated that TAS2R10 was broadly expressed in the CC SM and to some extent in the nerve fibers. Denatonium, chloroquine, SNAP, and isoproterenol cause potent dose-dependent SM relaxations. H2S production was decreased by NO and H2S synthase inhibitors, while it was enhanced by denatonium. In addition, denatonium increased the relaxations induced by GYY 4137 and SNAP but failed to modify EFS- and isoproterenol-induced responses. These results suggest neuronal and SM TAS2R10 expression in the rat CC, where denatonium induces a strong SM relaxation per se and promotes the H2S- and NO-mediated inhibitory gaseous neurotransmission. Thus, TAS2R10 might represent a valuable therapeutic target in ED.

TRPM8 channel activation induces relaxation in pudendal artery and corpus cavernosum: Can TRPM8 channel be a target to improve diabetic erectile dysfunction?

Erectile dysfunction (ED) is one of the most common and underestimated complications of diabetes. Previous studies have shown that TRPM8 activation triggers relaxation of internal pudendal arteries (IPA) with increased sensitivity in hypertensive rats. Despite the correlation between ED and diabetes, research on the role of TRPM8 channels in the IPA and corpus cavernosum (CC) in diabetes still needs to be elucidated. We hypothesized that preserved TRPM8 channel function in diabetic mice could be a therapeutic target for the treatment of ED. Male lean and db/db mice were euthanized, and the IPA were mounted on DMT wire myographs and CC were mounted on AVS organ bath for the measurement of isometric force. Concentration-response curves to icilin or menthol (TRPM8 agonists) were obtained. The CC TRPM8 channels expression was evaluated by western blot. Second harmonic generation was used to evaluate collagen deposition in IPA. Data are expressed as mean ± S.E.M of 3-5 mice. Non-linear regression curve was performed, and the maximum response (Emax) was analyzed using Student’s t test (p<0.05). Similar TRPM8 channel expression was observed in the CC from lean and db/db mice. Menthol-induced relaxation of the CC was reduced in diabetic mice (Emax: 105.00 ± 5.00%) compared to lean mice (Emax: 139.44 ± 15.91%) . Relaxant effect induced by icilin and menthol was similar between IPA from db/db (Emax icilin: 95.56 ± 0.86% and Emax menthol: 93.88 ± 2.33%) and lean (Emax icilin: 97.05 ± 0.87% and Emax menthol: 101.10 ± 1.75%) mice. Interestingly, pre-incubation with icilin (10-4M) for 30 minutes decreased the potency of phenylephrine-induced contraction compared to untreated IPA rings in both db/db and lean mice. In the IPA, diabetes decreased the sensitivity to acetylcholine compared to lean. However, the relaxation induced by acetylcholine was not changed by pre-incubation with icilin. Diabetic mice (db/db) IPA tended to have a decrease in arterial collagen content compared to lean mice. Although menthol-induced relaxation of the CC was reduced in diabetic mice, icilin and menthol were able to promote similar relaxation in IPA from diabetic and lean mice. In this way, TRPM8 function was preserved in IPA from diabetic mice. Icilin reduced sensitivity to phenylephrine in IPA from both mice. These data suggest that activation of TRPM8 could be a therapeutic target for the treatment of ED. SMSNA, NIH (RO1DK132948) and FAPESB This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Serum from Men with the Severe Form of COVID-19 Impairs the Nitric Oxide Signaling Pathway in Isolated Corpus Cavernosum from Mice: An In Vitro Study

Introduction. Erectile dysfunction (ED) is characterized by the inability to achieve and/or maintain an erection during sexual activity. Vascular-related diseases such as obesity, diabetes, aging, and hypertension are known risk factors that increase the prevalence of ED. The viral infection caused by SARS-CoV-2, the etiological agent of COVID-19, can evolve into mild to severe forms. Patients with comorbidities such as diabetes and obesity present a more severe state of the disease. The cytokine storm and reactive oxygen species associated with COVID-19 can lead to progressive systemic inflammation and vascular dysfunction. This study is aimed at assessing the in vitro effects of serum obtained from unvaccinated men who had the severe form of COVID-19 in isolated corpus cavernosum (CC) from healthy mice. Methods. Concentration-response curves to endothelium-dependent and endothelium-independent substances were carried out in isolated CC from mice after being incubated (3 hours) with serum obtained from patients with and without (control group) the severe form of COVID-19. qRT-PCR and western blotting were also carried out. Results. The relaxing responses induced by acetylcholine (ACh), a nitric oxide donor (sodium nitroprusside), soluble guanylate cyclase (sGC) stimulator (BAY 63-2521), and phosphodiesterase type 5 (PDE5) inhibitor (tadalafil) were significantly reduced in CC incubated with COVID-19 serum when compared with CC incubated with the control serum. Nonetheless, the relaxation induced by the sGC activator BAY 58-2667 was unaffected in CC stimulated with the COVID-19 serum. The coincubation of control or COVID-19 serum with a free radical scavenger (PEG-SOD; 150 UI/mL, 3 hours) significantly improved the relaxation induced by ACh. On the other hand, catalase did not improve ACh-induced relaxation in CC incubated with the sera. The gene expression for PDE5 and NADPH oxidase type 4 was increased in CC stimulated with COVID-19 serum in comparison to tissues stimulated with the control serum. The protein expression for sGC subunits was similar in both groups. Conclusion. Serum obtained from unvaccinated men who presented the severe form of COVID-19 impaired the relaxation induced by cyclic guanosine monophosphate-accumulating substances in CC from mice.

The Acute Effects and Mechanism of Ketamine on Nicotine-Induced Neurogenic Relaxation of the Corpus Cavernosum in Mice.

The present study aimed to investigate the acute effects and the mechanism of ketamine on nicotine-induced relaxation of the corpus cavernosum (CC) in mice. This study measured the intra-cavernosal pressure (ICP) of male C57BL/6 mice and the CC muscle activities using an organ bath wire myograph. Various drugs were used to investigate the mechanism of ketamine on nicotine-induced relaxation. Direct ketamine injection into the major pelvic ganglion (MPG) inhibited MPG-induced increases in ICP. D-serine/L-glutamate-induced relaxation of the CC was inhibited by MK-801 (N-methyl-D-aspartate (NMDA) receptor inhibitor), and nicotine-induced relaxation was enhanced by D-serine/L-glutamate. NMDA had no effect on CC relaxation. Nicotine-induced relaxation of the CC was suppressed by mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist), lidocaine, guanethidine (an adrenergic neuronal blocker), Nw-nitro-L-arginine (a non-selective nitric oxide synthase inhibitor), MK-801, and ketamine. This relaxation was almost completely inhibited in CC strips pretreated with 6-hydroxydopamine (a neurotoxic synthetic organic compound). Ketamine inhibited cavernosal nerve neurotransmission via direct action on the ganglion and impaired nicotine-induced CC relaxation. The relaxation of the CC was dependent on the interaction of the sympathetic and parasympathetic nerves, which may be mediated by the NMDA receptor.

Influence of lauric acid on the relaxation of corpus cavernosum in streptozotocin-induced diabetic male Wistar rats

BackgroundDiabetes mellitus is a global health challenge and has been recognised as a risk factor for erectile dysfunction. Dissatisfaction with standard medications has been reported by some patients, hence therapeutic plants are being considered as a viable alternative therapy, with their active components being investigated to create a standard regimen. Lauric acid is the most abundant constituent of coconut oil and is proposed to be responsible for its therapeutic properties. The corpus cavernosum plays an important role in erectile function with its relaxation favouring erection. This study thus sought to investigate the possible relaxant action and mechanism of lauric acid on the corpus cavernosum of diabetic male Wistar rats. Diabetes was induced by intraperitoneal injection of streptozotocin after which graded doses of lauric acid were administered orally to three groups of diabetic rats, once daily for 4 weeks. At the end of the experiment, the corpus cavernosal tissues of the rat penis were extracted. Following phenylephrine or potassium chloride (KCl)—induced contraction, relaxation response to acetylcholine and sodium nitroprusside was used to evaluate endothelium-dependent and nitric oxide-mediated relaxation, respectively.ResultsRelaxation response to acetylcholine, following pre-contraction with phenylephrine, was significantly decreased in the cavernosal tissues of diabetic untreated rats and was not significantly improved in lauric acid treated diabetic groups. Relaxation response to acetylcholine, following pre-contraction with KCl, was significantly decreased in the diabetic untreated group but was significantly improved in lauric acid treated diabetic groups at the lowest dose. Decreased relaxation response to sodium nitroprusside, following pre-contraction with phenylephrine in tissues of diabetic untreated rats, was significantly improved in lauric acid-treated diabetic groups at lower doses. Decreased relaxation response to sodium nitroprusside, following pre-contraction with KCl, was significantly improved in lauric acid-treated diabetic groups at all doses.ConclusionLauric acid improved relaxation of corpus cavernosum muscle in diabetic male rats by enhancing nitric oxide-mediated relaxing action of sodium nitroprusside and possibly inhibiting KCl-induced contraction.

Treatment with Resveratrol Reverses Priapism in the Sickle Cell Mouse

Introduction: Sickle cell disease (SCD) men display priapism. Townes and Berkeley SCD mice models are widely studied in basic sciences because they express 100% HbS in their circulating erythrocytes and exhibit features of priapism, and, as in SCD humans, this appears to be due to decreased nitric oxide (NO) signaling and increased oxidative stress, which leads to lower PDE5 in the penis. Thus, when an erectile stimulus occurs in vivo, cGMP accumulates into the cavernosal smooth muscle cells, rendering the penile vasculature uncontrollably dilated, and penile erection persists (i.e., priapism) as cGMP is not degraded as a consequence of PDE5 downregulation. Moreover, oxidative/nitrosative stress has been associated with priapism in SCD mice.Resveratrol (trans-3,5,4′-trihydroxystilbene) is a natural phytoalexin product with potent antioxidant activity found in peanuts, berries, and grapes. In this study, since decreased NO bioavailability and increased oxidative stress leads to lower PDE5 in the penis, we aimed to evaluate the effects of resveratrol on functional and molecular alterations of erectile function in SCD mice. We have focused on the dysregulated NO-cGMP-PDE5 pathway and oxidative/nitrosative stress markers (4-HNE and 3-nitrotyrosine) in the erectile tissue of SCD. Methods: Wild type (WT, C57BL/6) and Townes SCD transgenic male mice (3-5 mo old) were treated with resveratrol (100 mg /kg/day) or its vehicle daily for two weeks via gavage. Corpus cavernosum (CC) strips were mounted in isolated organ baths, and the relaxing responses to acetylcholine (ACh; endothelium-dependent response) and sodium nitroprusside (SNP; endothelium-independent response), as well as electrical-field stimulation (EFS; nitrergic relaxation), were obtained in CC strips precontracted with the α1-adrenergic receptor agonist phenylephrine (3-10 µM). Results: The cumulative addition of ACh (0.001-10 µM) produced concentration-dependent CC relaxations in WT and SCD groups, but the ACh potency (pEC50) value was higher (P<0.05) in CC of SCD compared to WT mice, which was reversed by resveratrol. Likewise, the nitrergic relaxation induced by EFS was also higher (P<0.05) in SCD mice compared to control mice (4 Hz: 30 ± 8 and 80 ± 5 %, respectively; n=5), which was reversed by resveratrol treatment. Similarly, SNP (0.01- 10 µM) produced concentration-dependent CC relaxations in WT and SCD groups, but, again, the maximal relaxations elicited by this agent were higher (P<0.05) in SCD (90 ± 1%) group compared to the WT mice (65 ± 6%), which were fully restored to WT values with resveratrol treatment (n=6). The mRNA expression for the PDE5 was reduced (P<0.05) by approximately 57% in penile tissues from SCD compared to the WT group, respectively. Resveratrol treatment restored (P<0.05) the mRNA expression of PDE5 in the penises from the SCD group (n=5-6). The protein expressions for 4-HNE and 3-nitrotyrosine (3-NT) were significantly higher (P<0.05) in erectile tissues from SCD compared to the WT group, which were reduced (P<0.05) by resveratrol treatment (n=6). In WT mice, PDE5, 4-HNE, and 3-NT protein expressions were not affected by resveratrol, as well as CC relaxations induced by ACh, SNP, and EFS. Conclusion: Resveratrol treatment reduced enhanced NO-mediated CC relaxations along with normalization of PDE5 expression and reduced oxidative stress markers expressions (3-NT and 4-HNE) in the penises from SCD. Therefore, resveratrol may constitute an additional strategy to prevent priapism in SCD. Financial Support: FAPESP.

Intravascular hemolysis leads to exaggerated corpus cavernosum relaxation: Implication for priapism in sickle cell disease

Patients with sickle cell disease (SCD) display priapism. Clinical studies have shown a strong positive correlation between priapism and high levels of intravascular hemolysis in men with SCD. However, there are no experimental studies that show that intravascular hemolysis promotes alterations in erectile function. Therefore, we aimed to evaluate the corpus cavernosum smooth muscle relaxant function in a murine model that displays intravascular hemolysis induced by phenylhydrazine (PHZ), as well as the role of intravascular hemolysis in increasing the stress oxidative in the penis. Corpus cavernosum strips were dissected free and placed in organ baths. Acetylcholine and electrical field stimulation (EFS)-induced corpus cavernosum relaxations in vitro were obtained. Increased corpus cavernosum relaxant responses to acetylcholine and EFS were observed in the PHZ group. Protein expression of heme oxygenase-1 increased in the corpus cavernosum of the PHZ group, but PDE5 protein expression was not modified. Preincubation with the heme oxygenase inhibitor 1J completely reversed the increased relaxant responses to acetylcholine and EFS in PHZ mice. Protein expression of NADPH oxidase subunit gp91phox, 3-nitrotyrosine, and 4-hydroxynonenal increased in the corpus cavernosum of the PHZ group, suggesting a state of oxidative stress. Basal cGMP production was lower in the PHZ group. Our results show that intravascular hemolysis promotes increased corpus cavernosum smooth muscle relaxation associated with increased HO-1 expression, as well as increased oxidative stress associated with upregulation of gp91phox expression. Moreover, our study supports clinical studies that point to a strong positive correlation between priapism and high levels of intravascular hemolysis in men with SCD.

Effects of Simulated Long Duration Spaceflight on Erectile Function

The goal of NASA along with other space agencies in the world is to send manned missions to the moon in the coming years, and eventually to Mars. The long‐term health risks of spaceflight have been attributed primarily to cosmic radiation and microgravity and the adverse effects as seen in the astronauts and model animals include DNA damage, mitochondrial dysregulation, oxidative damage, epigenetic changes, telomere length changes and microbiome shifts all of which affect the cardiovascular system. However, little is known about the effect of spaceflight on erectile function which is an important quality of life aspect for men. The aim of our study was to investigate the effect of simulated long duration space flight on erectile function. We hypothesized that both hindlimb unloading (HLU) and radiation will adversely affect erectile function. 86 adult male Sprague‐Dawley rats were used for these studies. Half the animals underwent 4 weeks of HLU, and all animals were divided into 3 groups: those that received sham radiation, 0.75 Gy, and 1.5 Gy galactic cosmic radiation, respectively at the Ground‐based GCR simulator at the NASA Space Radiation laboratory. The animals were then monitored for 6‐9 months before they were sacrificed, following which Corpus cavernosum (CC) and the distal internal pudendal arteries (dIPA) were harvested and used for ex vivo functional assessment. Tissue and wire myography studies were performed to assess adrenergic and endothelium‐dependent vasoconstrictions using phenylephrine (PE), norepinephrine, and endothelin. This was done by measuring the cumulative dose‐responses to the agonists in both the CC and dIPA. Endothelium‐dependent and ‐independent relaxations were also assessed using acetylcholine and diethylamine nononate. Non‐adrenergic non‐cholinergic (NANC) transmission was assessed using electrical stimulation (Estim); 30V electric pulses were delivered to the tissues with frequency ranging from 1‐32Hz following the administration of atropine and guanethidine and pre‐constriction with PE. Finally, Estim was done without atropine and guanethidine to assess the parasympathetic mediated relaxation in the tissues. The effects of HLU and radiation on the contractile and relaxation responses were assessed by two‐way repeated measures ANOVA. HLU and radiation significantly reduced both endothelium‐dependent and ‐independent vasodilatation in the dIPA and CC. Also, HLU and radiation significantly reduced the adrenergic constriction of CC in response to PE and norepinephrine. However, neither HLU nor radiation influenced the endothelium‐dependent vasoconstriction in the dIPA. Finally, radiation reduced the relaxation in both CC and dIPA while HLU increased the dIPA relaxation following Estim for both the parasympathetic mediated and NANC mediated responses. These results therefore showed the effects of HLU and radiation on erectile function, with exposure to cosmic radiation being primarily responsible for the detrimental effects. Further research needs to be done on this subject to show more mechanistically how spaceflight can affect erectile function and ways to combat the problem to ensure that astronauts can return to their normal sexual lives after long trips to space.

Erectile Dysfunction and Altered Contribution of KCa1.1 and KCa2.3 Channels in the Penile Tissue of Type-2 Diabetic db/db Mice

BackgroundActivation of endothelial small conductance calcium-activated K+ channels (KCa2.3) and intermediate conductance calcium-activated K+ channels (KCa3.1) leads to vascular relaxation. We found endothelial KCa2.3 down-regulation in the corpus cavernosum diminishes erectile function. AimWe hypothesized that in type-2 diabetic mice, the function of KCa2.3 and KCa1.1 channels is impaired in erectile tissue. MethodsErectile function was measured, and corpus cavernosum strips were mounted for functional studies and processed for qPCR and immunoblotting. OutcomesEffects of type 2 diabetes on erectile function, expression and function of calcium-activated potassium channels. ResultsIn anesthetized diabetic db/db mice, erectile function was markedly decreased compared to non-diabetic heterozygous db/+ mice, and the impairment was even more pronounced compared to normal C57BL/6 mice. qPCR revealed KCa2.3 and KCa1.1α channel expressions were upregulated in corpus cavernosum from db/db mice. Immunoblotting showed down-regulation of KCa2.3 channels in the corpus cavernosum from db/db mice. Acetylcholine relaxations were impaired while relaxations induced by the nitric oxide, donor SNP were unaltered in corpus cavernosum from db/db compared to C57BL/6 and db/+ mice. Apamin, a blocker of KCa2 channels, inhibited acetylcholine relaxation in corpus cavernosum from all experimental groups. In the presence of apamin, acetylcholine relaxation was markedly decreased in corpus cavernosum from db/db vs C57BL/6 and db/+ mice. An opener of KCa2 and KCa3.1 channels, NS309, potentiated acetylcholine relaxations in corpus cavernosum from db/+ and db/db mice. Iberiotoxin, a blocker of KCa1.1 channels, inhibited acetylcholine relaxation in corpus cavernosum from db/+ mice, while there was no effect in tissue from db/db mice. Clinical TranslationErectile function in diabetic db/db mice was severely affected compared to heterozygous and control mice, findings suggesting the non-diabetic db/+ and diabetic db/db mice for translational purpose can be used for drug testing on, respectively, moderate and severe erectile dysfunction. The altered expressions and impaired acetylcholine relaxation in the presence of apamin compared to C57BL/6 mice may suggest decreased KCa1.1 channel function may underpin impaired endothelium-dependent relaxation and erectile dysfunction in diabetic db/db mice. Strengths & LimitationsThe present study provides a mouse model for type 2 diabetes to test moderate and severe erectile dysfunction drugs. Decreased KCa1.1 channel function contributes to erectile dysfunction, and it is a limitation that it is not supported by electrophysiological measurements. ConclusionOur results suggest that the contribution of iberiotoxin-sensitive KCa1.1 channels to relaxation is reduced in the corpus cavernosum, while apamin-sensitive KCa2.3 channels appear upregulated. The impaired KCa1.1 channel function may contribute to the impaired erectile function in diabetic db/db mice.Comerma-Steffensen S, Prat-Duran J, Mogensen S, et al. Erectile Dysfunction and Altered Contribution of KCa1.1 and KCa2.3 Channels in the Penile Tissue of Type-2 Diabetic db/db Mice. J Sex Med 2022;19:697–710.

Evaluating the Effects of Low Carbohydrate and High Protein Diet on Erectile Function in Rats.

IntroductionCarbohydrate restriction in diet is becoming a popular means of losing weight nowadays, although it has been reported that excessive intake of low-carbohydrate and high-protein (LCHP) diet causes an adverse effect on cardiovascular function.AimTo investigate the influence of LCHP on erectile function in rats.MethodsA total of 48, 12-week-old rats were divided into 2 groups and either fed a LCHP diet (LCHP group) or a normal diet (Control group). Hematological examination, blood pressure evaluation, erectile function assessments as well as evaluations of the relaxation and contractile responses of corpus cavernosum were carried out in these rats by using standardized methods. Statistical analysis using 2-way ANOVA and Welch's t-test was conducted to examine the obtained data.Main Outcome MeasureAt the end of the study period, the evaluated outcomes to assess erectile function were intracavernosal pressure , mean arterial pressure , endothelial functions, nitric oxide (NO)-operated nerve functions and the expressions of endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and sphingosine-1-phosphate receptor 1 (S1P1).ResultsThe intracavernosal pressure / mean arterial pressure ratio was significantly lower in the LCHP group (P < .05) at 4 weeks. Compared to the Control group, the LCHP group exhibited significantly lower responses to ACh and EFS and a decreased nNOS mRNA expression. The results based on this animal model indicate that extreme carbohydrate restricted diet may affect erectile function. Our study identified that LCHP decreased erectile function in rats. A major limitation of this study is, due to the extreme condition of completely replacing carbohydrates with protein, that carbohydrate intake will be gradually increased in the future.ConclusionExtreme carbohydrate restriction and high protein in diet may cause ED with vascular endothelial dysfunction and a decrease in the relaxation response of the corpus cavernosum smooth muscle via NO-operated nerves.Kataoka T, Hidaka J, Suzuki J, et al. Evaluating the Effects of Low Carbohydrate and High Protein Diet on Erectile Function in Rats. Sex Med 2021;10:100500.

In vitro inhibition of phosphodiesterase type 4 enhances rat corpus cavernosum nerve-mediated relaxation induced by gasotransmitters

AimsNitric oxide (NO) and hydrogen sulfide (H2S) are involved in nerve-mediated corpus cavernosum (CC) relaxation. Expression of phosphodiesterase type 5 (PDE5) and type 4 (PDE4), cyclic guanosine monophosphate (cGMP)- and cyclic adenosine monophosphate (cAMP)-specific, respectively, has been described and PDE5- and PDE4-inhibitors induce cavernous smooth muscle relaxation. Whereas the NO/cGMP signaling pathway is well established in penile erection, the cAMP-mediated mechanism is not fully elucidated. The aim of this study is to investigate the localization and the functional significance of PDE4 in rat CC tone regulation. Main methodsWe performed immunohistochemistry for the detection of the PDE4A isoenzyme. Isometric tension recordings for roflumilast and tadalafil, PDE4 and PDE5 inhibitors, respectively, electrical field stimulation (EFS) and β-adrenoceptor agonist isoproterenol and endogenous H2S production measurement. Key findingsA marked PDE4A expression was detected mainly localized in the nerve cells of the cavernous smooth muscle. Furthermore, roflumilast and tadalafil exhibited strong corpus cavernous relaxations. Endogenous H2S production was decreased by NO and H2S synthase inhibitors and increased by roflumilast. Isoproterenol- and EFS-induced relaxations were increased by roflumilast. SignificanceThese results indicate that PDE4A is mainly expressed within the nerves cells of the rat CC, where roflumilast induces a potent corpus cavernous relaxation per se and potentiates the response induced by β-adrenoceptor activation. The fact that roflumilast enhances H2S production, as well as EFS-elicited responses suggests that PDE4 inhibitors modulate, in a positive feedback fashion, nerve-mediated relaxation induced by gasotransmitters, thus indicating a key role for neuronal PDE4 in penile erection.

Expression of MicroRNAs (miR-15b, miR-16, miR-138, miR-221, and miR-222) as Biomarkers of Endothelial Corpus Cavernosum Dysfunction in a Diabetic Alcoholic Murine Model.

IntroductionMicroRNAs (miRNAs) are short noncoding RNA molecules that regulate gene expression and are related to endothelial dysfunction (EnD). Recently, miRNAs have also been explored as potential biomarkers and target molecular therapy of erectile dysfunction (ED). Could the miRNAs be the tip of the iceberg of chronic arterial disease foreshadowed by the ED?AimTo investigate the expression of miR-15b, miR-16, miR-138, miR-221, and miR-222 in corpus cavernosum (CC) and peripheral blood in a rat model of endothelium dysfunction secondary to diabetes (DM) and alcohol consumption to assess potential endothelial lesion biomarkers.MethodsTwenty males Wistar rats were divided into 4 groups: control group (C), alcohol consumption group (A), diabetic group (D), diabetic-alcohol consumption group (D + A). DM was alloxan-induced and alcohol consumption was through progressive increase of ethanol concentration in drinkable water. After 7 weeks, miRNAs expressions from CC and blood sample were evaluated by real-time PCR. Functional assessment of CC was performed in an acetylcholine endothelium-dependent relaxation pharmacological study.Main Outcome MeasuremiRNA expression in CC and blood were evaluated; pharmacological study in CC strips was conducted to validate EnD.ResultsWe found that 3 miRNAs (miR-16, miR-221, and miR-222) were downregulated in the CC in the D+A group, while all 5 miRNAs were downregulated in the blood of D and D + A groups. The endothelium-dependent relaxation induced by acetylcholine was significantly decreased in groups A, D, and D + A. Diagnostic accuracy estimated by AUC, to discriminating groups A, D, and D + A from controls, was superior to >0.9 in all plasmatic miRNAs.ConclusionmiRNAs downregulation was identified in both CC and blood notably in DM associated with alcohol consumption animals (D + A), the greatest endothelial injury potential group. Serum miRNAs have also demonstrated high diagnostic accuracy properties in predicting CC relaxation dysfunction labeling EnD. RB Tiraboschi, FSL Neto, DP da Cunha Tirapelli, et al. Expression of MicroRNAs (miR-15b, miR-16, miR-138, miR-221, and miR-222) as Biomarkers of Endothelial Corpus Cavernosum Dysfunction in a Diabetic Alcoholic Murine Model. Sex Med 2021;9:100326.

089 Mirabegron for Erectile Dysfunction

PDE5 inhibitor is the only approved oral medication to treat erectile dysfunction (ED) in the US. However, there is a need for an alternative medication when PDE5 inhibitor treatment fails or there is a contraindication. The β3-adrenoceptor has been shown in human corpus cavernosum (CC). CC relaxation is induced by β3-adrenoceptor activation via cAMP-PKA dependent and/or cAMP-PKA independent pathway. Preclinical studies suggested mechanisms such as activation of K+ channels and closure of voltage-gated Ca2+ channels, cGMP accumulation by NO release and H2S pathway. However, the role of β3-adrenoceptor on penile erection in men is still unclear. Mirabegron is the first β3-adrenoceptor agonist that has been approved for the treatment of overactive bladder (OAB). The disorders of lower genitourinary tract such as OAB and ED share a common pathophysiologic mechanism. Mirabegron may act simultaneously in bladder and CC via β3-adrenoceptor activation and can offer a pharmacologic target for ED.

Erectile dysfunction is associated with defective L-cysteine/hydrogen sulfide pathway in human corpus cavernosum and penile arteries

H2S signaling was proposed to participate in erectile physiology. L-cysteine (CYS)/H2S pathway stimulation causes cGMP-dependent relaxation of human corpus cavernosum (HCC) and penile arteries (HPRA). The aim was to evaluate the impact of ED on CYS/H2S pathway at functional and molecular level in human penile vascular tissues. NaHS- and CYS-induced responses were evaluated in HCC and HPRA from organ donors without ED (NoED, n = 29) and from ED patients undergoing penile prosthesis insertion (n = 45). cGMP accumulation and cystathionine β-synthase and cystathionine γ-lyase expression were also determined.NaHS-induced relaxations were slightly but significantly impaired in HCC but not in HPRA from ED patients. In contrast, CYS-induced relaxations were markedly impaired in HCC (Emax 67.6 ± 4.9% vs 46.2 ± 4.6%, P < 0.01) and HPRA (Emax 80.8 ± 4.0% vs 48.1 ± 8.6%, P < 0.05) from men with ED. Impairment of CYS-induced responses was observed even after separating diabetic ED patients. In HPRA from ED patients, CYS- but not NaHS-induced vasodilation was significantly associated to endothelial function measured as vasodilatory capacity of acetylcholine (ACh) in these preparations (r2 = 0.481, P < 0.01). Impairment of CYS-induced relaxations was related to significant reduction in CYS-induced accumulation of cGMP in cavernosal tissue. Furthermore, the expression of H2S synthesizing enzymes was significantly reduced in HCC from ED patients with respect to NoED. This was confirmed by immunofluorescence in HCC and HPRA sections. ED involves impairment of CYS/H2S pathway in penile vascular tissues associated with decreased expression of H2S generating enzymes, CBS and CSE. These evidences support a therapeutic potential for modulation of CYS/H2S signaling in the management of ED.

A Rare Case of Recurrent Idiopathic Low-flow Priapism that Developed into a High-flow Priapism

Priapism, according to the American Urological Association is defined as a persistent penile erection that continues hours beyond sexual stimulation; typically, greater than 4 hours. Although priapism is a rare condition and has an unpredictable course in most presentation, it affects 5.36 per 100,000 male subjects per year [1]. Priapism is a urological emergency and delay in treatment or refractory cases can result in cavernous smooth muscle necrosis, fibrosis and penile shortening [2]. There are 2 categories of priapism-namely low-flow (ischemia, veno-occlusive) and high-flow (non-ischemic, arterial) [3,4]. There is a subset of ischemic priapism known as stuttering priapism which presents with recurrent incidences of ischemic priapism varying in length and is usually self-limiting [4]. Low-flow priapism occurs when an occlusive process inhibits the relaxation of the corpus cavernosum, thus the outflow of blood is impaired. The conditions associated with low-flow/ischemic priapism are as follows: sickle cell disease, vasoactive drugs, neoplastic diseases of the penis, urethra, prostate, bladder, kidney, gastrointestinal tract, leukemia, polycythemia, traumatic injury, hyperlipidemic parenteral nutrition, hemodialysis, heparin treatment, Fabry disease and neurologic conditions [3]. On the other hand, high-flow priapism occurs when there is increased arterial blood flow or pooling of blood. Conditions associated with high-flow priapism include traumatic arterio-cavernous fistula, vasoactive drugs, penile revascularization surgery, and neurologic conditions [3]. The mechanism of penile erection is a multifocal phenomenon that involves the nervous system, molecules (nitric oxide, cGMP, calcium), enzymes, and blood vessels. We present an interesting case of a patient with a history of recurrent priapism who converted from a low-flow priapism to a high-flow priapism, thought to be secondary to an arterio-cavernous fistula. Upon further review of PubMed and NIH database, there has been only few of such cases reported. We discuss the diagnostic process and management of high-flow priapism in this report.