Pro-erectile Effect Research Articles

(370) Overview of Nonclinical Studies of LIB-01, a Novel Promising Oral Drug Under Development for Treatment of Erectile Dysfunction

Abstract Introduction LIB-01 is a novel molecule being developed as an oral drug for the treatment of erectile dysfunction (ED). It is a semi-synthetic analog, developed based on research on active compounds identified in root bark that had been used for treatment of male sexual disability since time immemorial. Objective In preparation for clinical development, a number of nonclinical studies on erectile function were conducted in normal and diabetic rats with ED. Studies to investigate the mechanism supporting the pro-erectile effect of LIB-01 were also conducted. A summary of the results from the nonclinical research program is presented. Methods Erectile response elicited by electrical stimulation of the cavernous nerve (ES CN) in anaesthetized rats was assessed. Intracavernous and arterial blood pressures were monitored according to a standardized experimental procedure. Mechanism of action studies were conducted with rat cavernosal tissue samples using immunohistochemistry and in ex vivo/organ chamber experiments. The isometric tension studies were conducted on cavernosal strips from LIB-01 treated and untreated Wistar rats. Cavernosal strips from untreated rats were incubated with either LIB-01 or DMSO (control) and then pre-contracted by phenylephrine (PHE). Concentration- or frequency response curves were performed on PHE pre-contracted strips in 3 consecutive steps: (i) cumulative addition of increasing acetylcholine (ACh) concentrations, (ii) electrical field stimulation (EFS) with increasing frequencies, and (iii), cumulative addition of increasing sodium nitroprusside (SNP) concentrations. Results A statistically significant pro-erectile facilitatory effect of LIB-01 has been repeatedly evidenced in all the studies conducted in anaesthetized control Wistar rats, by oral or subcutaneous administration of LIB-01 at 15 mg/kg/d, with an effect in the similar range as iv sildenafil 0.3mg/kg, when compared. The pro-erectile effect of LIB-01 was not acute, instead, the effect gradually increased and remained for at least 7 days post treatment. In addition, LIB-01 significantly improved erectile responses in anaesthetized diabetic Goto-Kakizaki ED rats compared to vehicle-treated rats, demonstrating the pro-erectile effect of LIB-01 in a robust validated pathophysiological rat model of type 2 diabetes. Immunohistochemistry experiments on cavernosal tissue from LIB-01 treated normal rats showed that neither CD31 nor nNOS expression was altered, thus likely ruling out any effect of LIB-01 on cavernosal micro-vascularization or cavernosal nNOS. Furthermore, only at a high concentration (10-5 M) was there a slight increase in the endothelium dependent relaxations induced by ACh compared to vehicle while LIB-01 did not exert any effect neither on endothelium-independent relaxations induced by SNP nor on nitrergic relaxation induced by EFS of untreated cavernosal strips exposed ex-vivo to different concentrations of LIB-01. Conclusions LIB-01 is a novel molecule which displays a significant pro-erectile effect in anesthetized normal rats as well as in diabetic rats with ED. The pro-erectile effect of LIB-01 is not acute, instead, the effect gradually increases and remains for at least 7 days post-treatment. Results from several mechanistic studies lead to postulate that the mechanism of LIB-01 does not recruit the NO-cGMP pathway thereby differing from phosphodiesterase type 5 inhibitors. A first-in-human clinical trial with LIB-01 is planned to start in 2023. Disclosure Yes, this is sponsored by industry/sponsor: Dicot AB. Clarification: Industry initiated, executed and funded study. Any of the authors act as a consultant, employee or shareholder of an industry for: Dicot AB.

Intracavernosal onabotulinumtoxin a exerts a synergistic pro-erectile effect when combined with sildenafil in spontaneously hypertensive rats

<h3>Objectives</h3> Our overall aim was to provide experimental pharmacological evidence for the use of intracavernosal (ic) onabotulinumtoxinA alone or in combination with phosphodiesterase type 5 inhibitors for difficult-to-treat erectile dysfunction. We thus compared the effects of botulinum toxin A alone and botulinum toxin A combined with phosphodiesterase type 5 inhibitor, and a placebo treatment. <h3>Methods</h3> Erectile function was evaluated following cavernous nerve electrical stimulation at different frequencies in 4 groups (n = 8 / group) of anesthetized, spontaneously hypertensive rats. Rats were treated by onabotulinumtoxinA 10U or saline ic 1 week prior to erectile function testing and sildenafil (0.3 mg/kg) or saline iv 4 minutes prior to testing. Frequency-response curves were compared with a two-way ANOVA. <h3>Results</h3> Intracavernosal pressure/mean arterial pressure ratios were significantly increased by sildenafil and onabotulinumtoxinA ic versus the control condition. OnabotulinumtoxinA 10U ic combined with sildenafil significantly potentiated erectile responses. Area under the curve/mean arterial pressure ratio increased by 19% with sildenafil, by 15% with onabotulinumtoxinA ic and by 58% with the combined treatment. <h3>Conclusions</h3> Both onabotulinumtoxinA ic, and sildenafil, significantly improved erectile responses in spontaneously hypertensive rats, however the effect was greatly amplified when the treatments were combined. These results support further studies into the mechanisms behind the pro-erectile effect of BTX-A ic, as well as multicenter randomized control trials to evaluate the safety and efficacy of BTX-A combined with sildenafil for difficult-to-treat ED. <h3>Conflicts of Interest</h3> No conflict of interest

Intracavernosal OnabotulinumtoxinA Exerts a Synergistic Pro-Erectile Effect When Combined With Sildenafil in Spontaneously Hypertensive Rats

Botulinum toxin A (BTX-A) has a variety of uses in medicine. Some evidence suggests that intracavernosal (ic) BTX-A injection administered in addition to phosphodiesterase type 5 inhibitors (PDE5-Is) could effectively treat erectile dysfunction (ED) in insufficient responders to PDE5-Is. To provide experimental pharmacological evidence for the use of onabotulinumtoxinA ic alone or in combination with PDE5-Is for difficult-to-treat ED. We thus compared the effects of BTX-A ic alone and BTX-A ic combined with PDE5-I iv, and a placebo treatment ic or iv. Erectile function was evaluated following cavernous nerve electrical stimulation (6 V, 1-millisecond pulse, 45-second duration) at different frequencies (0, 2, 3, 4, 5, 7.5, and 10 Hz) in 4 groups (n = 8 / group) of anesthetized, spontaneously hypertensive rats, a robust animal model of ED of vascular origin. Rats were treated by onabotulinumtoxinA 10U or saline ic 1 week prior to erectile function testing and sildenafil (0.3 mg/kg) or saline iv 4 minutes prior to testing. Frequency-response curves were compared with a 2 way ANOVA. Both onabotulinumtoxinA ic, and sildenafil iv significantly improved erectile responses in spontaneously hypertensive rats, however the effect was greatly amplified when the treatments were combined. Intracavernosal pressure and/or mean arterial pressure ratios were significantly increased by sildenafil and onabotulinumtoxinA ic versus the control condition. OnabotulinumtoxinA 10U ic combined with sildenafil iv significantly potentiated erectile responses. Area under the curve and/or mean arterial pressure ratio increased by 19% with sildenafil iv, by 15% with onabotulinumtoxinA ic and by 58% with the combined treatment following cavernous nerve electrical stimulation at 6V, 1 ms, 10 Hz: these stimulation parameters elicited the maximal erectile response. These data provide a pharmacological rationale for the combined administration of onabotulinumtoxinA ic and sildenafil iv since the effects of both treatments were potentiated when their administration was combined. First evidence of a synergistic pro-erectile effect of BTX-A combined with PDE5-I, however the mechanism behind the pro-erectile effect of BTX-A ic remains hypothetical. These results support further studies into the mechanisms behind the pro-erectile effect of BTX-A ic, as well as multicenter randomized control trials to evaluate the safety and efficacy of BTX-A ic combined with sildenafil for difficult-to-treat ED.

Sexual responses of male rats to odours from female rats in oestrus are not affected by female germ-free status

Rats detect and use odorant molecules as a source of information about their environment. Some of these molecules come from conspecifics, and many arise as by-products from microbial activity. Thus, compared to conventionally housed rats, germ-free rats are raised in an environment with fewer odorants, but this reduction is rarely quantified. Using gas chromatography–mass spectrometry, we found that germ-free rat faeces samples contained half as many volatile molecules than conventional rat faeces (52 vs 109 (±2.4) molecules; P < 0.001) and overall these were only 12% as abundant. We then investigated if odours from female germ-free rats in oestrus would have pro-erectile effects in conventional male rats. For this aim, conventionally housed Brown Norway (BN) rats (n = 16) with sexual experience with either Fischer or BN females, were exposed to four different odour types: faeces from germ-free Fischer rat in oestrus, faeces from conventional rats in oestrus and di-oestrus (either from Fischer or BN), and a control (either 1-hexanol or male rat faeces). The number of penile erections per test as well as the duration of freezing behaviour was significantly higher with the oestrous odours (germ-free and conventional) compared to the control, with intermediate responses to the di-oestrous faeces. The findings indicate that, despite a significantly reduced composition in terms of volatiles compared to conventionally housed rats, the faeces of germ-free rats contain sufficient odorants to evoke sexual responses in conventional male rats. Oestrous odours of rats thus appear not to be of microbial origin.

1117 - Additive pro-erectile effect of low intensity-shockwave therapy (Li-ESWT) delivered by Aries® combined with sildenafil in spontaneously hypertensive rats (SHR)

1117 - Additive pro-erectile effect of low intensity-shockwave therapy (Li-ESWT) delivered by Aries® combined with sildenafil in spontaneously hypertensive rats (SHR)

The impact of surgical treatments for lower urinary tract symptoms/benign prostatic hyperplasia on male erectile function

Lower urinary tract symptoms (LUTS)/benign prostatic hyperplasia (BPH) is common in adult men and can impair erectile function (EF). It was believed surgical treatments for this illness can improve EF due to the relief of LUTS while they were also reported harmed EF as heating or injury effect. Current network meta-analysis aimed to elucidate this discrepancy.Randomized controlled trials (RCTs) were identified. Direct comparisons were conducted by STATA and network meta-analysis was conducted by Generate Mixed Treatment Comparison. Random-effects models were used to calculate pooled standard mean difference and 95% confidence intervals and to incorporate variation between studies.Eighteen RCTs with 2433 participants were analyzed. Nine approaches were studied as transurethral resection of the prostate (TURP), plasmakinetic resection of the prostate (PKRP), plasmakinetic enucleation of the prostate (PKEP), Holmium laser enucleation of the prostate (HoLEP), Holmium laser resection of the prostate (HoLRP), photoselective vaporization of the prostate (PVP), Thulium laser, open prostatectomy (OP), and laparoscopic simple prostatectomy (LSP). In direct comparisons, all surgical treatments did not decrease postoperative International Index of Erectile Function (IIEF)-5 score except PVP. Moreover, patients who underwent HoLEP, PKEP, Thulium laser, and TURP had their postoperative EF significantly increased. Network analysis including direct and indirect comparisons ranked LSP at the highest position on the variation of postoperative IIEF-5 score, followed by PKRP, HoLEP, TURP, Thulium laser, PKEP, PVP, HoLRP, and OP. In subgroup analysis, only PVP was found lower postoperative EF in the short term and decreased baseline group, whereas TURP increased postoperative IIEF-5 score only for patients with normal baseline EF. However, HoLEP and PKEP showed pro-erectile effect even for patients with decreased baseline EF and short-term follow-up. Our novel data demonstrating surgical treatments for LUTS/BPH showed no negative impact on postoperative EF except PVP. Moreover, HoLEP and PKEP were found pro-erectile effect for all subgroups. New technologies, such as LSP, PKRP, and Thulium laser, were ranked at top positions in the network analysis, although they had no pro-erectile effect in direct comparison due to limited original studies or poor baseline EF. Therefore, further studies and longer follow-up are required to substantiate our findings.

Clinical and Laboratory Assessment of Supplementation with Marine Collagen Peptides and Selected Antioxidants in Men with Mild-to-Moderate Erectile Dysfunction

Objectives: Notwithstanding great progress in the management of erectile dysfunction (ED) by phosphodiesterase inhibitors, safety concerns hinder their routine use in men with mild-to-moderate forms. Several plant-derived supplements have been proven acceptable substituents of conventional anti-ED drugs. Most anti-ED drugs/supplements act through nitric oxide (NO)-dependent molecular pathways, due to NO-induced smooth muscle relaxation of the local Corpus cavernosum vessels. A randomised single-blind self-controlled clinical investigation recently showed that dietary supplementation with marine collagen peptides (MCP) in combination with selected antioxidants remarkably enhanced nitrite/nitrate plasma levels along with skin rejuvenation and general energising (hormesis-like) effects. This pilot study was designed to reveal possible clinical action of this supplement towards ED and its mechanisms. Methods: Fifteen otherwise healthy men (age range 55-61 years), free of sex organ diseases/malformations, diabetes or pre-diabetes, atherosclerosis, metabolic syndrome, cardio-vascular diseases or testosterone deficiency suffering from the mild-to-moderate erectile dysfunction diagnosed by the International Index of Erectile Function (IIEF-5 ≤ 20) were recruited for a pilot, clinical trial. The participants were given 2 capsules containing MCP +antioxidants a day for 30 consecutive days. Several functions of circulating phagocytes (granulocytes and monocytes), plasma levels of macrophage-targeting cytokines and nitrites/nitrates, expression of genes encoding inducible and endothelial nitric oxide synthase (iNOS and eNOS, respectively) and ATP content in phagocytes, and activity of glutathione peroxidase (GPX) in erythrocytes were recorded twice, at enrolment and at the cessation of the oral supplementation. Eighteen age-matched men without ED and 41 healthy subjects of both sexes (age range 20-65 years) served as controls. Results: The supplementation was proven safe, not causing any adverse reaction. The IIEF-5 score was increased in 100% of participants, of 3-4 points on average. The MCP+antioxidants supplementation lead to activation of phagocyte defence functions (phagocytosis, intracellular bacterial killing, and reactive oxygen species production), to increased plasma levels of nitrites/nitrates, TNF-alpha and INF-gamma, to increased phagocyte levels of ATP, and to up-regulation of iNOS RNA. Although statistically significantly increased, these parameters remained within the normal range of values. There were no changes in the eNOS expression, GPX activity, and IL-10 levels. Discussion: We suggest a novel mechanism of possible regulation of penile erection through the initial selective stimulation of Toll-like receptors on circulating phagocytes, to convert them into defensive M1 cells producing enhanced quantities of TNF-alpha and INF-gamma, along with a hormesis-like moderate induction of iNOS. The measured increase of ATP levels might facilitate phagocyte NO release by the interaction with adenosine receptors. Conclusions: For the first time, marine collagen peptides combined with selected antioxidants are shown to have pro-erectile effects, through different mechanisms than those described previously. This oral supplementation could be considered as a safe and effective alternative to anti-ED drugs in the case of mild-to-moderate ED. More mechanistic studies are needed, along with larger-scale multi-centre placebo-controlled clinical trials.

MP52-07 EXPRESSION AND DISTRIBUTION OF CANNABINOID RECEPTORS IN THE HUMAN SEMINAL VESICLES

water-filled cage. Shockwaves were delivered by a calibrated probe yielding a controlled energy flux density of 0.09mJ/mm2 attached to a compact electrohydraulic unit with a focused shockwave source (Omnispec ED1000, Medispec Ltd, USA). Following a 4-week wash-out period, erectile function was assessed by electrical stimulation of the cavernous nerve in anesthetized rats and the effects of Li-ESWT alone or in combination with acute iv sildenafil (0.3mg/kg) were evaluated. Subsequently, ex vivo isometric tension studies were performed on CC from the same rats. RESULTS: Erectile function in GK rats was markedly impaired compared to age-matched Wistar rats and associated with altered endothelium-dependent, -independent and nitrergic mediated relaxations in CC. Either acute sildenafil or Li-ESWT significantly improved erectile responses in GK rats. Ratios of intracavernosal pressure and area under the curve /mean arterial pressure were significantly increased by 18% (p<0.001), 17% (p<0.05) and 32% (p<0.001), 23% (p<0.01), respectively versus untreated GK. This proerectile facilitator effect of Li-ESWT was not associated to improved endothelium-dependent, -independent or nitrergic reactivity of CC. The combination of Li-ESWT with sildenafil significantly potentiated the effect of Li-ESWT alone. CONCLUSIONS: Li-ESWT improves the erectile function of diabetic GK rats. Surprisingly, this effect is not mediated by a NO/ cGMP-dependent mechanism. Furthermore, this study shows additive effects when Li-ESWT is combined with a single dose of sildenafil.

Dopamine agonist-induced penile erection and yawning: A comparative study in outbred Roman high- and low-avoidance rats

The effects on penile erection and yawning of subcutaneous (SC) injections of the mixed dopamine D1/D2-like agonist apomorphine (0.02–0.2mg/kg) were studied in outbred Roman high- (RHA) and low-avoidance (RLA) male rats, two lines selectively bred for their respectively rapid versus poor acquisition of the active avoidance response in the shuttle-box, and compared with the effects observed in male Sprague–Dawley (SD) rats. Apomorphine dose–response curves were bell-shaped in all rat lines/strains. Notably, more penile erections and yawns were recorded mainly in the ascending part of these curves (e.g., apomorphine 0.02–0.08mg/kg) in both RLA and RHA rats compared to SD rats, with RLA rats showing the higher response (especially for yawning) with respect to RHA rats. Similar results were found with PD-168,077 (0.02–0.2mg/kg SC), a D4 receptor agonist, which induced penile erection but not yawning. In all rat lines/strains, apomorphine responses were markedly reduced by the D2 antagonist L-741,626, but not by the D3 antagonist, SB277011A, whereas the D4 antagonists L-745,870 and FAUC213 elicited a partial, yet statistically significant, inhibitory effect. In contrast, the pro-erectile effect of PD-168,077 was completely abolished by L-745,870 and FAUC213, as expected. The present study confirms and extends previously reported differences in dopamine transmission between RLA and RHA rats and between the SD strain and the Roman lines. Moreover, it confirms previous studies supporting the view that dopamine receptors of the D2 subtype play a predominant role in the pro-yawning and pro-erectile effect of apomorphine, and that the selective stimulation of D4 receptors induces penile erection.

Hydrogen sulfide promotes nitric oxide production in corpus cavernosum by enhancing expression of endothelial nitric oxide synthase

Recently, hydrogen sulfide (H2S) has been identified as a potential therapy for ED. However, a thorough understanding of its molecular mechanisms of action would be essential to develop H2S as a new therapy for ED. In this study, the effect of H2S on nitric oxide (NO) production, especially through the expression of constitutive nitric oxide synthase (NOS) isoforms-endothelial NOS (eNOS) and neuronal NOS (nNOS) in rat corpus cavernosum (CC) were explored. Real-time PCR studies subsequent to in vitro treatment of sodium hydrosulfide hydrate (NaHS), a stable H2S donor, showed increases in eNOS but not nNOS mRNA. Western blot studies confirmed that the exogenously applied NaHS increased eNOS but not nNOS protein expression in the rat CC. Furthermore, NaHS did not alter the expressed amounts of Caveolin-1 (CAV-1), a dominant inhibitory interaction partner of eNOS, in these tissues. Not surprisingly, NaHS also enhanced the NO production in eNOS-associated membrane fraction of rat CC. Taken together, we ascertain that H2S could exert its proerectile effects by augmenting NO pathway. It appears that H2S would be particularly useful in improving the clinical outcome of ED patients, whose erectile impairment is due to an inherent attenuation of the endothelial NO formation in the cavernosum.

Neuroendocrine regulatory peptide-1 and neuroendocrine regulatory peptide-2 influence differentially feeding and penile erection in male rats: Sites of action in the brain

The effect of NERP-1 and NERP-2, two recently discovered VGF-derived peptides, on feeding and penile erection was studied after injection into the lateral ventricles, the lateral hypothalamus, the arcuate nucleus or the paraventricular nucleus of the hypothalamus. NERP-2 (1–5nmol), but not NERP-1 (2–4nmol), increased feeding in a dose-dependent manner when injected into the lateral ventricles or bilaterally into the lateral hypothalamus but not into the arcuate or the paraventricular nucleus. The effect of NERP-2 given into the lateral ventricles was found in the first, but not in the second 60min after treatment, and was antagonized by SB-408124, an orexin-1 receptor antagonist given into the lateral ventricles or the arcuate nucleus, but not into the paraventricular nucleus. However, SB-408124 was unable to reduce NERP-2-induced feeding when injected bilaterally into the lateral hypothalamus before NERP-2 given also bilaterally into the lateral hypothalamus. In contrast, NERP-1, but not NERP-2, induced penile erection in a dose-dependent manner when injected into the lateral ventricles or the arcuate nucleus, but not into the paraventricular nucleus or the lateral hypothalamus. The pro-erectile effect of NERP-1 was not prevented by the prior injection of d(CH2)5Tyr (Me)2-Orn8-oxytocin or SB-408124 into the lateral ventricles. The present results suggest that while NERP-2 facilitates feeding by acting in the lateral hypothalamus, possibly by increasing orexin activity in the arcuate nucleus, NERP-1 facilitates penile erection by acting in the arcuate nucleus with a mechanism not related to orexin or oxytocin.

Combination of BAY 60-4552 and Vardenafil Exerts Proerectile Facilitator Effects in Rats With Cavernous Nerve Injury: A Proof of Concept Study for the Treatment of Phosphodiesterase Type 5 Inhibitor Failure

Combination of BAY 60-4552 and Vardenafil Exerts Proerectile Facilitator Effects in Rats With Cavernous Nerve Injury: A Proof of Concept Study for the Treatment of Phosphodiesterase Type 5 Inhibitor Failure

Dopamine D2-like receptor agonists induce penile erection in male rats: differential role of D2, D3 and D4 receptors in the paraventricular nucleus of the hypothalamus

Pramipexole, a dopamine D3/D2 receptor agonist, induces penile erection when administered subcutaneously (s.c.) or into the paraventricular nucleus of the hypothalamus of male rats, like apomorphine, a mixed D1/D2 receptor agonist, and PD 168,077, a D4 receptor agonist. A U-inverted dose–response curve was found with pramipexole and apomorphine, but not with PD 168,077 (0.025–0.5 mg/kg s.c.). Pramipexole effect was abolished by L-741,626, a D2 receptor antagonist (2.5 and 5 mg/kg s.c.) and raclopride, a D2/D3 receptor antagonist (0.025 and 0.1 mg/kg s.c.), but not by SB277011A (2.5 and 10 mg/kg s.c.) or FAUC 365 (1 and 2 mg/kg s.c.), two D3 receptor antagonists, or L-745,870 (1 and 5 mg/kg i.p.), a D4 receptor antagonist. Similar results were found with apomorphine (0.08 mg/kg s.c.), although its effect was also partially reduced by L-745,870. In contrast, PD 168,077 effect was abolished by L-745,870, but not L-741,626, SB277011A, FAUC 365 or raclopride. Similar results were found when dopamine agonists (5–200 ng/rat) and antagonists (1–5 μg/rat) were injected into the paraventricular nucleus. However, no U-inverted dose–response curve was found with any of the three dopamine agonists injected into this nucleus. As pramipexole- and apomorphine-induced penile erection was reduced mainly by D2, but not D3 or D4 antagonists, D2 receptors are those that mediate the pro-erectile effect of these dopamine agonists. Although the selective stimulation of paraventricular D4 receptors induces penile erection, D4 receptors seem to play only a modest role in the pro-erectile effect of the above dopamine agonists.

Effects of Hydrogen Sulfide on Erectile Function and Its Possible Mechanism(s) of Action

The current pharmacotherapy for erectile dysfunction (ED) relies significantly on the use of phosphodiesterase type 5 (PDE5) inhibitors, but quite a proportion of ED patients are resistant to this therapy, necessitating a search for an alternative treatment. We reviewed available published data to analyze current evidence of hydrogen sulfide (H(2) S) as a novel pharmacotherapeutic agent with supportive role in sexual function. To discuss the role of H(2) S in erectile function, its possible mechanism of action, and how this knowledge may be exploited for therapeutic use. Pubmed and Medline search was conducted to identify original articles and reviews. Data from peer-reviewed publications. Animal studies using different species, including in vitro study done in humans, show evidence of H(2) S's pro-erectile effects. The mechanism behind is still unclear, but evidence in literature points out the involvement of K(+) (ATP) channel, modulation of protein with anti-erectile effects, as well as involvement of the nitrergic pathway through a complex cross-talk. A new drug called H(2) S-donating sildenafil (ACS6), which incorporated an H(2) S-donating moiety in sildenafil, has been developed. While more studies are still needed, this heralded a new pharmacotherapeutical approach, which is multipronged in nature. Given the mounting evidence of H(2) S's role in erectile function and how it appears to achieve its pro-erectile effects through different mechanisms, H(2) S represents a potentially important treatment alternative or adjunct to PDE5 inhibitors.

Subchronic treatment with fluoxetine attenuates the proerectile effect of Aspidosperma ulei Markgr (Apocyanaceae)

Objective:To evaluate the ability of acute or chronic treatment with fluoxetine to alter the proerectile effect of Aspidosperma ulei alkaloid-rich fraction (F3-5).Materials and Methods:In the first series of experiments, three groups of mice received either a single intraperitoneal injection of vehicle, F3-5 (25 mg/kg) or fluoxetine (10 mg/kg) + F3-5. Three behavioral responses were counted over a period of 30 min: erection, erection-like response and genital grooming. In a second series of experiments, animals treated for 13 days with fluoxetine or fluoxetine + F3-5 were assessed.Results:A. ulei has been suggested to have proerectile effect in mice. Subchronic (13-d) treatment with fluoxetine resulted in a reduction in the number erections in F3-5-treated mice.Conclusion:Sexual dysfunction associated with antidepressant treatment continues to be a major compliance issue for antidepressant therapy. Acute administration of fluoxetine resulted in a near total reversal of the proerectile effect of F3-5.

Oxytocin induces penile erection when injected into the ventral subiculum: Role of nitric oxide and glutamic acid

Oxytocin (100 ng) induces penile erection when injected unilaterally into the ventral subiculum of the hippocampus of male rats. The pro-erectile effect started mostly 30 min after treatment and occurred 15 min after an increase in both nitric oxide (NO) production, measured by the concentration of NO(2)(-) and NO(3)(-), the main metabolites of newly formed NO, and extra-cellular glutamic acid concentration in the dialysate obtained from the ventral subiculum by intracerebral microdialysis. These responses were abolished by d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin (2 microg), an oxytocin receptor antagonist, S-methyl-L-thiocitrulline (SMTC), a selective inhibitor of neuronal NO-synthase (25 microg), and haemoglobin, a NO scavenger (25 microg), given into the ventral subiculum before oxytocin. Unlike d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin, SMTC and haemoglobin, (+)MK-801 (5 microg), a noncompetitive antagonist of NMDA receptors abolished oxytocin-induced penile erection, but reduced only partially the increase in NO production and extra-cellular glutamic acid. As NMDA (0.25-1 microg) injected into the ventral subiculum induces penile erection episodes, which also occurred with an increase of NO production and extra-cellular glutamic acid, and NMDA responses were abolished by (+)MK-801 (5 microg), but not by SMTC (25 microg) or haemoglobin (25 microg), injected into the ventral subiculum, these results show that oxytocin injected into the ventral subiculum increases NO production by activating its own receptors. NO in turn increases glutamic acid neurotransmission, leading to penile erection, possibly through neural (glutamatergic) efferent projections from the ventral subiculum to extra-hippocampal brain areas (e.g., prefrontal cortex) modulating the activity of mesolimbic dopaminergic neurons.

Oxytocin injected into the ventral subiculum or the posteromedial cortical nucleus of the amygdala induces penile erection and increases extracellular dopamine levels in the nucleus accumbens of male rats

Oxytocin (20-100 ng) was found to be able to induce penile erection when injected unilaterally into the ventral subiculum or the posteromedial cortical nucleus of the amygdala of male rats. The pro-erectile effect started mostly 30 min after treatment and was abolished by the prior injection of d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin (1-2 microg), an oxytocin receptor antagonist, into the ventral subiculum or posteromedial cortical nucleus. Oxytocin-induced penile erection occurred 15 min after the increase in the concentration of extracellular dopamine and its metabolite 3,4-dihydroxyphenylacetic acid in the dialysate obtained from the nucleus accumbens, which was also abolished by d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin. The pro-erectile effect of oxytocin was also reduced by cis-flupentixol (2 and 5 microg), a dopamine receptor antagonist, injected into the nucleus accumbens, and by (+)MK-801 (5 microg), a noncompetitive N-methyl-d-aspartate receptor antagonist, injected into the ventral tegmental area, but not into the nucleus accumbens. Together with studies showing that glutamatergic efferents from the ventral subiculum/posteromedial cortical nucleus of the amygdala to other areas of the limbic system modulate the activity of mesolimbic dopaminergic neurons, these findings suggest that oxytocin injected into these areas increases glutamatergic neurotransmission in the ventral tegmental area. This, in turn, activates mesolimbic dopaminergic neurons, leading to penile erection. These results provide evidence that the ventral subiculum and the posteromedial cortical nucleus of the amygdala participate in a neural circuit that controls not only the consummatory aspects of sexual behaviour (e.g. penile erection and copulatory performance), but also its motivational/reward aspects, confirming a key role of oxytocin and dopamine in these processes.

Proerectile Effects of Dopamine D2-Like Agonists Are Mediated by the D3 Receptor in Rats and Mice

Dopamine D(2)-like agonists induce penile erection (PE) and yawning in a variety of species, effects that have been suggested recently to be specifically mediated by the D(4) and D(3) receptors, respectively. The current studies were aimed at characterizing a series of D(2), D(3), and D(4) agonists with respect to their capacity to induce PE and yawning in the rat and the proerectile effects of apomorphine [(R)-(-)-5,6,6a,7-tetrahydro-6-methyl-4H-dibenzo-[de,g]quinoline-10,11-diol hydrochloride] in wild-type and D(4) receptor (R) knockout (KO) mice. All D(3) agonists induced dose-dependent increases in PE and yawning over a similar range of doses, whereas significant increases in PE or yawning were not observed with any of the D(4) agonists. Likewise, D(2), D(3), and D(4) antagonists were assessed for their capacity to alter apomorphine- and pramipexole (N'-propyl-4,5,6,7-tetrahydrobenzothiazole-2,6-diamine dihydrochloride)-induced PE and yawning. The D(3) antagonist, PG01037 [N-{4-[4-(2,3-dichlorophenyl)-piperazin-1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide hydrochloride], inhibited the induction of PE and yawning, whereas the D(2) antagonist, L-741,626 [3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole], reversed the inhibition of PE and yawning observed at higher doses. The D(4) antagonist, L-745,870 [3-(4-[4-chlorophenyl]piperazin-1-yl)-methyl-1H-pyrrolo[2,3-b]pyridine trihydrochloride], did not alter apomorphine- or pramipexole-induced PE or yawning. A role for the D(3) receptor was further supported because apomorphine was equipotent at inducing PE in wild-type and D(4)RKO mice, effects that were inhibited by the D(3) antagonist, PG01037, in both wild-type and D(4)R KO mice. Together, these studies provide strong support that D(2)-like agonist-induced PE and yawning are differentially mediated by the D(3) (induction) and D(2) (inhibition) receptors. These studies fail to support a role for the D(4) receptor in the regulation of PE or yawning by D(2)-like agonists.

Synergistic actions of apomorphine and m-chlorophenylpiperazine on ejaculation, but not penile erection in rats

It has been suggested that dopamine (DA) and serotonin (5-HT) and their receptors, particularly D(2)-like and 5-HT(2C) receptors, may play a significant role in the control of male sexual function. The purpose of this study was to investigate whether the combination of a dopamine receptor agonist apomorphine and a 5-HT(2) receptor agonist m-CPP would potentiate penile erection and ejaculation in male rats. Systemic administration of either apomorphine (0.01-0.1 mg/kg, s.c.) or m-CPP (0.01-0.3 mg/kg, i.p.) dose-dependently elicited penile erections, but did not induce ejaculation. When combined, there was a drastic increase in both the incidence of ejaculation and the amount of ejaculated seminal materials, while the proerectile effect induced by each drug was not potentiated. The proejaculatory effect induced by the combination of apomorphine (0.1 mg/kg, s.c.) and m-CPP (0.3 mg/kg, i.p.) was completely blocked by pretreatment with the D(2)-like receptor antagonists haloperidol and sulpiride, but not by the D(1)-like receptor antagonist SCH-23390. The synergistic action for ejaculation was also blocked by domperidone, the D(2)-like receptor antagonist that dose not cross the blood-brain barrier. The rats pretreated with the 5-HT(2C) receptor antagonist SB242084 did not show the synergistic action by the combination of apomorphine and m-CPP, whereas the rats pretreated with the 5-HT(2A) receptor antagonist ketanserin and the 5-HT(2B) receptor antagonist SB204741 showed the combination-induced synergistic action. These results suggest that the combination of a small dose of apomorphine and m-CPP potently and selectively facilitates the ejaculatory response through the activation of D(2)-like and 5-HT(2C) receptors, respectively. The D(2)-like receptors involved in the synergistic action may be, at least in part, located in the peripheral sites.

5-HT2C receptor activation is a common mechanism on proerectile effects of apomorphine, oxytocin and melanotan-II in rats

5-Hydroxytryptamine (5-HT), dopamine, oxytocin and melanocortin pathways are known to be involved in the induction of penile erections in rats. Although a dopamine–oxytocin–5-HT link in the central nervous system has been suggested to be important to the control of penile erections, the 5-HT receptor subtype that mediates dopamine–oxytocin–5-HT action and the relationship between the dopamine–oxytocin–5-HT pathway and melanocortin pathway have not been fully elucidated. In this study, in order to clarify these matters, we examined the effects of a selective 5-HT2B/5-HT2C receptors antagonist, 1-(1-methylindol-5-yl)-3-(3-pyridyl)urea (SB200646) and a selective 5-HT2C receptor antagonist, 6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-yl carbamoyl] indoline (SB242084) on penile erections induced by a dopamine receptor agonist, 10, 11-dihydroxyaporphine (apomorphine), oxytocin, or a melanocortin receptor agonist, melanotan-II (MT-II) in rats. SB200646 at 10 mg/kg and SB242084 at 3 mg/kg, these doses which completely antagonize penile erections induced by 5-HT2C receptor agonists, m-chlorophenylpiperazine (mCPP) and (S)-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-methylethylamine (YM348), significantly inhibited penile erections elicited by apomorphine, oxytocin or MT-II. In addition, in order to clarify further the suggestion that the 5-HT pathway projecting from medulla oblongata to lumbosacral spinal site and lumbosacral 5-HT2C receptor are involved in the induction of penile erection, we also examined the proerectile effect of YM348 in spinal and a 5-HT depletor, p-chlorophenyl alanine (pCPA)-treated rats. YM348 induced intracavernous pressure increase in spinal and pCPA-treated rats as well as normal rats. These results suggest that 5-HT2C receptor in lumbosacral spinal sites mediates not only dopamine–oxytocin–5-HT action but melanocortin action on penile erections, and that the 5-HT pathway is located downstream from melanocortin pathway as well as the dopamine–oxytocin pathway.