Regulation Of Penile Erection Research Articles

Molecular and spatial signatures of human and rat corpus cavernosum physiopathological processes at single-cell resolution

The composition and cellular heterogeneity of the corpus cavernosum (CC) microenvironment have been characterized, but the spatial heterogeneity at the molecular level remains unexplored. In this study, we integrate single-cell RNA sequencing (scRNA-seq) and spatial transcriptome sequencing to comprehensively chart the spatial cellular landscape of the human and rat CC under normal and disease conditions. We observe differences in the proportions of cell subtypes and marker genes between humans and rats. Based on the analysis of the fibroblast (FB) niche, we also find that the enrichment scores of mechanical force signaling vary across different regions and correlate with the spatial distribution of FB subtypes. Invitro, the soft and hard extracellular matrix (ECM) induces the differentiation of FBs into apolipoprotein (APO)+ FBs and cartilage oligomeric matrix protein (COMP)+ FBs, respectively. In summary, our study provides a cross-species and physiopathological transcriptomic atlas of the CC, contributing to a further understanding of the molecular anatomy and regulation of penile erection.

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.

Role of the lateral preoptic area and the bed nucleus of stria terminalis in the regulation of penile erection

To elucidate the role of the preoptic area (POA) in the regulation of penile erection, we examined the effects of electrical stimulation in and around the POA on penile erection in rats, which was assessed by changes in pressure in the corpus spongiosum of the penis (CSP) and electromyography (EMG) of the bulbospongiosus (BS) muscle. In unanesthetized and anesthetized rats, four types of responses were induced by stimulation in and around the POA; (1) normal type responses, which were similar to spontaneously occurring erections, characterized by slow increase in CSP pressure and sharp peaks concurrent with BS muscle bursting; (2) muscular type responses, which included sharp CSP pressure peaks (muscular component) with almost no vascular component; (3) mixed type responses, which included a sequence of high-frequency CSP peaks followed by low-frequency CSP peaks; and (4) micturition type responses, which had higher-frequency and lower-amplitude CSP peaks than other responses which were identical to those of normal micturition. In unanesthetized condition, erections were evoked by stimulation of the lateral preoptic area (LPOA), medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), paraventricular nucleus (PVN), reuniens thalamic nucleus (Re) and lateral septum (LS). Lower-intensity stimulation evoked erections from the LPOA, BST, PVN and RE, but not the MPOA. In anesthetized condition, stronger stimuli were required and effective sites were restricted to the LPOA, MPOA and BST. These findings suggest that the lateral and medial subdivisions of the preoptic area play different roles in mediating penile erection.

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.

Penile erection and micturition events triggered by electrical stimulation of the mesopontine tegmental area

The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) play a crucial role in the regulation of rapid eye movement (REM) sleep. Because penile erection occurs during REM sleep, the involvement of the LDT in penile erection was examined in unanesthetized head-restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced the following three CSP pressure patterns: 1) a full erection pattern indistinguishable from the nonevoked or spontaneous erection, characterized by a slow increase in CSP pressure with additional sharp CSP peaks associated with BS muscle bursts, 2) a muscular pattern characterized by sharp CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, and 3) a mixed-type response characterized by high-frequency CSP pressure peaks followed by a full erection response. Full erections were evoked in and around the LDT, including more medially and ventrally. The sites for inducing mixed-type events were intermingled with the sites that triggered full erections in the anterior half of the LDT, whereas they were separated in the posterior half. The sites for muscular responses were lateral to the sites for full erections. Finally, a CSP pressure response identical to micturition was evoked in and around the Barrington's nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in the regulation of penile erection. Moreover, different anatomical areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.

GH- deficiency as an unexpected cause of erectile dysfunction (ED)

Objectives: Experimental data suggest a direct involvement of the GH/IGF-1 axis in the regulation of penile erection by dose dependant stimulation of endothelial nitric oxid formation. Moreover, in healthy men systemic GH serum levels significantly increased during penile tumescence. The present study was designed to better evaluate a potential involvement of GH deficiency (GHD) in a subgroup of patients with ED. Material and Methods: Serum IGF-1 was measured in 100 unselected patients with a diagnosis of ED for more than six months.Patients with severe organogenetic or psychogenetic causes of ED were excluded. If IGF-1 serum levels were below the age- adjusted 10th percentile dynamic testing of the GH axis was performed (insulin- tolerance- test, combined arginine/GHRH- test). Patients with a peak GH response of 33kg/m2. 15 subjects showed no exclusion criteria and were tested by the ITT. 4 of them showed a partial GHD and 2 a severe GHD in both tests. Control of other pituitary axes and a neuroradiological control by MRT showed no signs of any other pituitary disease. Conclusions: Our results suggest that ED is associated with unexpected failure of GH secretion in adults in an unexpected high proportion. Despite the good experimental evidence of a link between GHD and ED direct testing by GH substitution is warranted to evaluate a causal link between both conditions.

C-type natriuretic peptide in reproduction, pregnancy and fetal development.

C-type natriuretic peptide (CNP) belongs to the natriuretic peptide family that consists of three structurally related peptides with a 17-amino acid ring linked by a disulfide bond. In contrast to atrial and brain natriuretic peptides that are mainly cardiovascular hormones, CNP acts predominantly in an autocrine/paracrine fashion, is commonly considered to be an endothelial hormone with antimitogenic properties, and is characterized as a regulator of endochondral ossification. Its biological effects are mediated by an intracellular cGMP accumulation via specific membrane-bound guanylyl cyclase B (GC-B) activation. There is growing evidence that this peptide is also involved in various reproductive processes as well as in embryonic and fetal development. In rodents, CNP and its receptor are highly expressed in the uterus and ovaries with specific regulation during the estrous cycle. During pregnancy, CNP mRNA is detectable in mice embryos and shows an organ-specific expression in maternal reproductive tIssues with the highest concentration in the placenta. This could indicate a defined biological function of the CNP/GC-B/cGMP axis in gestation e.g. antagonizing vasoconstrictive peptides like angiotensin II. In humans, besides a postulated fetal de novo synthesis of CNP, both the peptide and its receptor are expressed in the placenta and myometrium with opposite regulation of CNP in pregnancies complicated by pre-eclampsia or intrauterine growth retardation. Since the maternal plasma levels do not reflect these alterations, one can conclude that this part of the natriuretic peptide system acts locally suggesting that CNP-stimulated cGMP release exhibits organ-specific effects. Importantly, CNP has also become a peptide with a distinct role in male reproductive processes, since endocrine function of the testis and the regulation of penile erection are regulated by the CNP/GC-B axis. This review gives a comprehensive overview of the multiple functions of CNP in reproduction and pregnancy as well as in embryonic and fetal development.

Ca2+-activated Cl- channels in corpus cavernosum smooth muscle: a novel mechanism for control of penile erection.

Little is known of the excitatory mechanisms that contribute to the tonic contraction of the corpus cavernosum smooth muscle in the flaccid state. We used patch-clamp electrophysiology to investigate a previously unidentified inward current in freshly isolated rat and human corporal myocytes. Phenylephrine (PE) contracted cells and activated whole cell currents. Outward current was identified as large-conductance Ca(2+)-activated K(+) current. The inward current elicited by PE was dependent on the Cl(-) gradient and was inhibited by niflumic acid, indicative of a Ca(2+)-activated Cl(-) (Cl(Ca)) current. Furthermore, spontaneous transient outward and inward currents (STOCs and STICs, respectively) were identified in both rat and human corporal myocytes and derived from large-conductance Ca(2+)-activated K(+) and Cl(Ca) channel activity. STICs and STOCs were inhibited by PE and A-23187, and combined 8-bromoadenosine cAMP and 8-bromoadenosine cGMP decreased their frequency. When studied in vivo, chloride channel blockers transiently increased intracavernosal pressure and prolonged nerve-evoked erections. This report reveals for the first time Cl(Ca) current in rat and human corpus cavernosum smooth muscle cells and demonstrates its key functional role in the regulation of penile erection.

RhoA/Rho-kinase: a novel player in the regulation of penile erection.

Current research has centered around the role of nitric oxide in the stimulation of cavernosal vasodilation and erection. However, recent evidence from our lab details the importance of endogenous vasoconstrictor mechanisms in maintaining a flaccid penile state, and further demonstrates that the inhibition of endogenous vasoconstriction is sufficient to stimulate erection in a rat model. In this article, we suggest inhibition of endogenous vasoconstriction as a potential therapeutic avenue in the treatment of erectile dysfunction. We also speculate on potential physiologic mechanisms by which endogenous vasoconstriction is inhibited in order for arousal-initiated vasorelaxation, and erection, to occur.

Possible role of bradykinin and angiotensin II in the regulation of penile erection and detumescence

Objectives. To examine the functional effects of bradykinin (BK) and angiotensin II (AN II) on isolated human cavernous tissue and to detect any changes in the AN II levels in cavernous and peripheral blood samples taken from healthy volunteers at different functional conditions of the penile erectile tissue. Metabolites of the renin-angiotensin system and endothelium-derived vasoactive substances are known to be involved in the regulation of arterial vascular tone. The human corpus cavernosum (HCC), consisting of endothelial and smooth muscle cells, can be regarded as a compartment comparable to the vascular system. Methods. The relaxing and contracting properties of BK and AN II on isolated HCC were investigated using the organ bath technique. Tissue levels of adenosine-3,5-cyclic monophosphate (cAMP) and guanosine-3,5-cyclic monophosphate (cGMP) were determined using specific radioimmunoassays, after exposing isolated HCC strips in a dose-dependent manner to BK, forskolin, and sodium nitroprusside. Blood samples were drawn simultaneously from the corpus cavernosum and cubital vein of 34 healthy volunteers at stages of penile flaccidity, tumescence, rigidity, and detumescence. Penile erection was induced by audiovisual and tactile stimulation. AN II levels were determined using a radioimmunoassay. Results. In vitro, BK, forskolin, and sodium nitroprusside elicited dose-dependent relaxation of norepinephrine-induced tension of isolated HCC, and AN II evoked dose-dependent contraction of the HCC strips. The relaxing potency of BK was paralleled by its ability to elevate the intracellular levels of cAMP and cGMP. In vivo, the AN II levels in the cavernous plasma increased from 21.8 ± 4.6 pg/mL in the flaccidity phase to 27.9 ± 10 pg/mL in the detumescence phase. In the peripheral plasma, the AN II levels were 17.2 ± 6.2 to 19.5 ± 6.5 pg/mL in the respective penile stages. Thus, the mean AN II levels in the cavernous blood were about 30% higher than in the blood samples taken from the cubital vein. In the cavernous blood, the increase in the AN II plasma levels in the detumescence phase (27.9 ± 10 pg/mL) was statistically significant. Conclusions. Our results suggest that penile cavernous smooth muscle tone is partially balanced by kinin-induced relaxation and AN II-induced contraction. Since the tissue and plasma levels of both peptides are regulated by the activity of the angiotensin-converting enzyme, there might be a rationale for the use of angiotensin-converting enzyme inhibitors in the treatment of erectile dysfunction associated with arterial hypertension.

Molecular studies of human connexin 43 (Cx43) expression in isolated corporal tissue strips and cultured corporal smooth muscle cells

Intercellular communication plays an important role in erectile function. The goal of this study, therefore, was two-fold. Firstly, to determine if cultured corporal smooth muscle cells provide a valid model system for evaluating the role of junctional communication to erectile physiology, and secondly, to explore the possibility that there may be age-related alterations in Cx43 mRNA expression. Human corpus cavernosum tissue was obtained from 31 patients with a mean age of 58 (range 27-89), while cell cultures were developed from 21 distinct patients with a mean age of 57 (range 26-59). Northern blots revealed that mRNA for Cx43 was expressed at detectable levels in all samples examined. It migrated as a transcript with an apparent size of 3.1 Kb. Western blots revealed the presence of multiple bands of Cx43 protein in both tissues and cells. However, Cx43 protein in tissue predominantly migrated as a 45 kDa band, while the Cx43 from cultured cells predominantly migrated as 41 kDa band. Cx43 mRNA expression was similarly heterogeneous in both frozen tissues and cultured cells. An approximately 3-5-fold increase in Cx43 mRNA levels was observed in cultured cells relative to frozen tissue, but the expression of Cx43 mRNA was not further altered upon passaging (p1-5). When Cx43 mRNA levels were normalized, and expressed as a ratio of the Cx43/beta-tubulin mRNA, there was a significant negative correlation between patient age and Cx43 levels on frozen tissues, but not on cultured cells. We conclude that: (1) There is similar heterogeneity/variability in Cx43 mRNA levels in frozen tissues and cultured cells derived from human corpus cavernosum. (2) That the expression of Cx43 mRNA in cultured cells is sufficiently stable, and similar to, expression levels in tissue as to provide a valid and physiologically relevant model system for further studying the role(s) of Cx43 in the regulation of penile erection. (3) There is a statistically significant, albeit modest, negative correlation between the Cx43/beta-tubulin ratio and patient age in frozen corporal tissue strips, but not on cultured corporal smooth muscle cells. Such observations provide further evidence for the plasticity of intercellular communication in the erectile process. Moreover, the similarities in the apparent regulation of Cx43 mRNA levels and that of the putative 'housekeeping' gene beta-tubulin, may suggest that Cx43 is constitutively synthesized in this tissue.

Renin Angiotensin System in Rabbit Corpus Cavernosum: Functional Characterization of Angiotensin II Receptors

Purpose The regulation of the corporal smooth muscle tone is important in the process of penile erection. Although specific angiotensin (ANG) II binding to and effects of ANG II on some reproductive structures have been studied, the presence of the renin-angiotensin system has not yet been defined in the corpus cavernosum. ANG II is formed from ANG I by angiotensin I-converting enzyme (ACE). ANG II and ANG I produce contractions in vascular smooth muscles. Two subtypes of ANG II receptors (AT1 and AT2) have been characterized. The purpose of the present experiments was to determine whether the renin-angiotensin system regulates rabbit corpus cavernosum smooth muscle tone. Materials and Methods A strip of rabbit corpus cavernosum was mounted in an organ chamber to measure the isometric tension. The specific binding for 125 I-ANG II was characterized by in vitro autoradiography. Results ANG II and ANG I, precursor of ANG II, contracted corpus cavernosum smooth muscle dose-dependently, but the response of smooth muscle to ANG I was 10-fold less than that to ANG II. Contractile responses of smooth muscle to ANG II and ANG I were blocked by Dup 753, a specific inhibitor of ANG II type 1 receptor, but not by PD 123,319, a specific inhibitor of ANG II type 2 receptor. The effect of ANG I was attenuated by captopril, an inhibitor of ACE. Specific binding sites for 125 I-ANG II were found in the corpus cavernosum. The dissociation constant (K d 2) was 5.32 +/− 1.65 nM. and maximum binding capacity (B max) was 305.72 +/− 85.24 amol/mm. 2 Specific binding of 125 I-ANG II was displaced by Dup 753 (10 sup −6 M) but not by PD 123,319 (10 sup −5 M). The inhibitory constant (K i) for Dup 753 was 8.09 +/− 2.51 nM. Conclusion The present results suggest that the renin-angiotensin system is involved in the regulation of corpus cavernosum smooth muscle tone of rabbit and the ANG II receptor subtype AT1 is important in the regulation of penile erection.

Parasympathetic nerves in penile erectile tissue of the rat contain choline acetyltransferase

Choline acetyltransferase (ChAT), a biochemical marker of cholinergic neurons, was measured in the erectile tissue of intact rats and in rats in which postganglionic fibers from the pelvic plexus were interrupted. ChAT activity in the denervated erectile tissue fell by 56% compared to control tissues. Acetylcholinesterase positive (AChE+) nerves also fell by about 48%. Penile neurons distal to the lesion probably account for the residual ChAT activity and remaining AChE+ nerve fibers in erectile tissue. These results indicate that acetylcholine is an important neurotransmitter in the regulation of penile erection.

Oxytocin: an extremely potent inducer of penile erection and yawning in male rats

The intracerebroventricular (i.c.v.) injection of oxytocin, in doses ranging from 5 to 90 ng (5–90 pmol) induced penile erection and yawning in male rats. Such response was not induced by doses of the peptide higher than 100 ng, nor by equimolar doses of i.c.v. [Arg 8]vasopressin, ACTH-(1–24), α-MSH, rat corticotropin-releasing factor (rCRF), delta sleep-inducing peptide, neurotensin or substance P. Oxytocin-induced penile erection and yawning were prevented by atropine and morphine, but not by methylatropine or the opiate antagonist naloxone. Haloperidol, a dopamine receptor antagonist, was ineffective at low doses; it partially prevented penile erection but not yawning at high doses. Since oxytocin is present not only in the neurohypophysis but also in other brain areas, our results suggest that oxytocin is implicated in the regulation of penile erection and yawning, and provide further evidence that oxytocin acts as a neuropeptide in the central nervous system.