Vasoactive intestinal polypeptide (VIP) as a possible neurotransmitter involved in penile erection

Vasoactive intestinal polypeptide/phentolamine for intracavernosal injection in erectile dysfunction

Erectile dysfunction (ED) is becoming an increasingly common problem and although oral therapies offer first-line treatment for many men, they are contraindicated or ineffective in substantial groups of patients. Intracavernosal injection (ICI) therapy is the most effective nonsurgical treatment for ED and offers an effective alternative to oral therapy. Sufficient arterial blood supply and a functional veno-occlusive mechanism are prerequisites in the attainment and maintenance of a functional erection. Invicorp (Plethora Solutions, London, UK) is a combination of vasoactive intestinal polypeptide (VIP) 25 microg and phentolamine mesylate 1 or 2 mg for ICI in the management of moderate to severe ED. The two active components have complementary modes of action; VIP has a potent effect on the veno-occlusive mechanism, but little effect on arterial inflow, whereas phentolamine increases arterial blood flow with no effect on the veno-occlusive mechanism. Clinical studies showed that Invicorp is effective in >or=80% of men with ED, including those who have failed to respond to other therapies and, unlike existing intracavernosal therapies, is associated with a very low incidence of penile pain and virtually negligible risk of priapism. We estimate that there are >5.9 million men in the USA alone for whom oral ED drugs are not a viable treatment option, and for whom Invicorp might offer a safe and effective alternative.

The effect of chronic renal failure on phosphodiesterase inhibitor-induced relaxation responses in rabbit cavernosal strips

Erectile dysfunction is common in men with chronic renal failure. Previously nitrergic and endothelium-dependent relaxation responses have been shown to be reduced in chronic renal failure rabbits. We have therefore investigated the efficacy of phosphodiesterase inhibitors on the corpora cavernosa obtained from uremic rabbits. Uremia was induced with 5/6 nephrectomy and 4 weeks later cavernosal tissue strips were isolated. The relaxant effect of phosphodiesterase 5 inhibitors, zaprinast (1-300 microM) and sildenafil (0.01-300 microM), phosphodiesterase 3 inhibitor amrinone (1-100 microM) and non-specific phosphodiesterase inhibitor papaverine (1-300 microM) were investigated on phenylephrine (10 microM)-induced tone. We found a shift in the dose-response curve of only phosphodiesterase 5 inhibitors. These results suggest that the decreased production or availability of endogenous nitric oxide in chronic renal failure animals leads to decreased efficacy of phosphodiesterase 5 inhibitors to induce relaxation.

Characterization of VIP and PACAP receptors in cultured rat penis corpus cavernosum smooth muscle cells and their interaction with guanylate cyclase-B receptors

Penile corpus cavernosum smooth muscle relaxation can be induced by both cyclic AMP and cyclic GMP-elevating agents, but possible interactions between these two signalling pathways are still poorly understood. Using in vitro cultured rat penile corpus cavernosum smooth muscle (CCSM) cells, we have characterized the local expression and functional activities of receptors for the cAMP-elevating peptides, PACAP and VIP, and for the cGMP-elevating peptides, CNP and ANP. Stimulation of the cells with various concentrations of PACAP(-27/-38) or VIP resulted in rapid and dose-dependent increases in cyclic AMP levels. RT-PCR analyses revealed gene expression of PAC(1) and VPAC(2) but not of VPAC(1) receptors in the cells. The natriuretic peptide, CNP, and the nitric oxide donor, sodium nitroprusside, were capable of enhancing cyclic GMP formation, indicating the presence of membrane-associated in addition to soluble guanylate cyclase (sGC) activities in these cells. Findings that cyclic GMP formation was preferentially activated by CNP but not by the related peptide, ANP, were consistent with RT-PCR analyses, demonstrating gene expression of the CNP receptor, GC-B, but not of the ANP receptor, GC-A, in these cells. Prior exposure of the cells to 10(-8) M PACAP resulted in a marked down-regulation of GC-B activity, whereas sGC was not affected. These findings provide functional and molecular evidence for the presence of three receptors, PAC(1), VPAC(2) and GC-B, involved in cyclic nucleotide signalling in penile CCSM cells. The observed cross-talk of the PACAP/VIP receptors with GC-B but not with sGC may have implications for the therapy of erectile dysfunction.

Detection of low-molecular-mass plasma peptides in the cavernous and systemic blood of healthy men during penile flaccidity and rigidity--an experimental approach using the novel differential peptide display technology

OBJECTIVES

To use Differential Peptide Display (DPD) technology to evaluate the patterns of low-molecular-mass peptides and small proteins in the systemic and cavernous blood taken from healthy adult male volunteers during the penile stages of flaccidity and rigidity. Results from basic research implicate a role of various peptides in the control of mammalian penile erectile tissue. Nevertheless, it is not yet known which particular peptides are essential in the regulation of penile flaccidity, tumescence, rigidity, and detumescence.

METHODS

Five healthy male subjects were exposed to visual and tactile erotic stimuli to elicit penile erection. Whole blood was simultaneously aspirated from the corpus cavernosum and cubital vein during penile flaccidity and rigidity. Plasma aliquots were subjected to DPD analysis by means of matrix-assisted-laser-desorption-ionization mass mapping and electrospray-ionization quadrupole--time-of-flight mass spectrometry.

RESULTS

High-resolution two-dimensional peptide mass mapping revealed differences in the systemic and cavernous plasma samples related to penile flaccidity and rigidity. Distinct signals were recognized in the cavernous but not in the systemic plasma obtained during flaccidity. These signals were not registered in the plasma samples obtained from the corpus cavernosum during rigid erection. Although one signal was identified as the blood coagulation-activating peptide XIIIa, the remaining two signals could not be related to any known peptide. These signals may represent unknown local peptidergic factors that might be involved in the regulation of penile flaccidity.

CONCLUSIONS

Our study demonstrates that DPD is a feasible method for detecting differences in the cavernous and systemic blood in relation to the different functional conditions of the penile erectile tissue. Additional studies using DPD should include the analysis of blood samples taken from the cavernous meshwork of healthy subjects during penile tumescence and detumescence to establish DPD as a valuable tool in contemporary corpus cavernosum basic research.

Effects of endothelial impairment by saponin on the responses to vasodilators and nitrergic nerve stimulation in isolated canine corpus cavernosum

1. Responsiveness to EDRF-releasing substances and inhibitory nerve stimulation of canine isolated penile corpus cavernosum with and without saponin treatment were investigated. 2. Histological studies demonstrated that saponin did not detach endothelial cells from underlying tissues, but induced degenerative changes in the endothelial cells selectively. 3. In the cavernous strips contracted with phenylephrine, addition of acetylcholine, sodium nitroprusside, ATP and Ca2+ ionophore A23187 induced relaxations, but substance P and bradykinin did not change the muscle tone. 4. Acetylcholine-induced relaxation was significantly attenuated but not abolished by NG-nitro-L-arginine (L-NOARG). L-arginine restored the response inhibited by L-NOARG. The L-NOARG resistant relaxation was not influenced by 1H[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) but was suppressed in the strips contracted with K+. Treatment with saponin abolished the relaxation elicited by acetylcholine and A23187 but did not influence the response to nitroprusside and ATP. The ATP-induced relaxation was attenuated by aminophylline. 5. Transmural electrical stimulation at 2-20 Hz produced endothelium-independent relaxations which were abolished by tetrodotoxin and L-NOARG but unaffected by treatment with saponin. In saponin-treated cavernous strips, the neurogenic relaxation was not affected by acetylcholine, physostigmine, atropine and vasoactive intestinal peptide (VIP) but was abolished by ODQ. 6. It is concluded that acetylcholine-induced relaxations are endothelium-dependent and mediated partly by NO and also by other substances from the endothelium. The endothelium-independent relaxation to ATP is likely to be mediated by P1 purinoceptors. The function of nitrergic nerve does not seem to be prejunctionally modulated by acetylcholine and VIP.

Nitrergic relaxation of the horse corpus cavernosum. Role of cGMP

The involvement of nitric oxide (NO) and the mechanisms mediating neurogenic relaxation were investigated in the horse corpus cavernosum. NADPH-diaphorase activity was expressed in nerve fibres around arteries and muscular bundles in the horse trabecular tissue. Relaxations in response to electrical field stimulation were tetrodotoxin (10(-6) M)-sensitive, indicating their neurogenic origin. The NO synthase inhibitor, L-NO-arginine (L-NO-Arg, 3 x 10(-5) M), abolished the electrically induced relaxations, which were significantly reversed by L-arginine (3 x 10(-3) M). Exogenous NO (10(-6)-10(-3) M) evoked relaxations which were unaffected by L-NO-Arg. 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 5 x 10(-6) M), an inhibitor of guanylate cyclase activation by NO, reduced the relaxations in response to electrical stimulation and exogenous NO. Iberiotoxin (3 x 10(-8) M) or apamin (5 x 10(-7) M), inhibitors of large and small conductance Ca2+-activated K+ channels, respectively, and glibenclamide (3 x 10(-6) M), a blocker of ATP-sensitive K+ channels, failed to modify the relaxations with NO. It is suggested that NO is present in nerve fibres of the horse corpus cavernosum and relaxes smooth muscle through a guanylate cyclase-dependent mechanism. Neither Ca2+-activated nor ATP-sensitive K+ channels seem to be involved in these relaxations.

Monkey corpus cavernosum relaxation mediated by NO and other relaxing factor derived from nerves

Isolated monkey corpus cavernosum muscle strips contracted with prostaglandin F2 alpha and treated with prazosin responded to transmural electrical stimulation with frequency-related relaxations that were abolished by tetrodotoxin. The nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) significantly attenuated but did not abolish the response; L-arginine reversed the inhibition. The neurogenic relaxation was not influenced in the strips treated with atropine or calcitonin gene-related peptide (CGRP)-(8-37), a CGRP-receptor antagonist, and those desensitized to vasoactive intestinal polypeptide (VIP) or pituitary adenylate cyclase-activating polypeptide (PACAP). Nerve fibers containing NADPH diaphorase were histochemically demonstrated in cavernous tissues. The relaxant response resistant to the NO synthase inhibitor was abolished by high K+ and tetrabutylammonium but was unaffected by glibenclamide, charybdotoxin, apamin, ouabain, SKF-525a, a cytochrome P-450 inhibitor, and oxyhemoglobin. It is concluded that neurogenic relaxations of monkey corpus cavernosum muscle is associated partly with NO released as a neurotransmitter and that other relaxing factor(s) possibly responsible for K+ channel opening also participates; however, the type of K+ channel involved is not determined. Acetylcholine, VIP, CGRP, PACAP, and the Na+ pump do not seem to be involved in the neurogenic relaxation.

Inhibition of penile erection in rats by a long-acting somatostatin analogue, octreotide (SMS 201-995)

OBJECTIVE

To assess the effect of a new somatostatin analogue (SMS 201-995, octreotide) on erectile function in rats.

MATERIALS AND METHODS

Animals were fasted and anaesthetized intraperitoneally with pentobarbital. A cannula was placed in the trachea and the femoral vein cannulated for intravenous infusion. The hypogastric and pelvic nerve, major pelvic ganglion, and the nerve fibres to the lower genitourinary tract were identified. In 20 animals, these nerves were stimulated unilaterally using bipolar silver-wire electrodes; the stimulation was repeated every 15 min for 1 h. Twenty animals were divided into two equal groups; after measuring penile erection to obtain basal values, the animals received either saline or 50 micrograms SMS 201-995 over 1 h and 30 min later, the stimulation was repeated.

RESULTS

After administering SMS 201-995 or saline, the levels of penile erection reduced linearly in both groups, but SMS 201-995 caused a greater decrease than in the control group (P < 0.05) and from baseline (P < 0.01) at all times.

CONCLUSION

SMS 201-995 inhibits penile erection in rats and the systems may serve as an in vivo animal model for further investigation.

Comparison of neurogenic contraction and relaxation in canine corpus cavernosum and penile artery and vein

Functional roles of autonomic efferent nerves were compared in the isolated canine corpus cavernosum, penile artery and penile vein that participate in the penile erection by changing blood distribution. Nicotine produced moderate contraction in the arterial strips, but only a slight or no contraction in the corpus and venous strips. The contraction was suppressed or reversed to a relaxation by prazosin. Under alpha 1-adrenoceptor blockade, relaxations induced by nicotine were in the order of the corpus > artery > > vein. The response was abolished by NG-nitro-L-arginine (L-NA) and restored by L-arginine. The responses to nicotine and exogenous nitric oxide (NO) were abolished by oxyhemoglobin. The relaxant response to transmural electrical stimulation at 5 Hz was greater in the corpus than venous strips treated with prazosin, and it was abolished by L-NA. Contractions caused by nicotine under treatment with L-NA were greater in the artery than in the vein and corpus. Histochemical studies demonstrated nerve fibers containing NO synthase and tyrosine hydroxylase immunoreactivity in the corpus cavernosum, artery and vein. It is concluded that the canine corpus cavernosum, penile artery and penile vein are innervated by adrenergic, vasoconstrictor and nitroxidergic, vasodilator nerves; neurogenic vasodilatation is predominant in the corpus muscle, whereas neurogenic vasoconstriction predominates in the artery. Such a different functioning of the nerves may be responsible for the penile erection.

Involvement of nitric oxide in the non-adrenergic non-cholinergic neurotransmission of horse deep penile arteries: role of charybdotoxin-sensitive K(+)-channels

1. The involvement of nitric oxide (NO) and the signal transduction mechanisms mediating neurogenic relaxations were investigated in deep intracavernous penile arteries with an internal lumen diameter of 600-900 microns, isolated from the corpus cavernosum of young horses. 2. The presence of nitric oxide synthase (NOS)-positive nerves was examined in cross and longitudinal sections of isolated penile arteries processed for NADPH-diaphorase (NADPH-d) histochemistry. NADPH-d-positive nerve fibres were observed in the adventitia-media junction of deep penile arteries and in relation to the trabecular smooth muscle. 3. Electrical field stimulation (EFS) evoked frequency-dependent relaxations of both endothelium-intact and denuded arterial preparations treated with guanethidine (10(-5) M) and atropine (10(-7) M), and contracted with 10(-6) M phenylephrine. These EFS-induced relaxations were tetrodotoxin-sensitive indicating their non-adrenergic non-cholinergic (NANC) neurogenic origin. 4. EFS-evoked relaxations were abolished at the lowest frequency (0.5-2 Hz) and attenuated at higher frequencies (4-32 Hz) by the NOS inhibitor, NG-nitro-L-arginine (L-NOARG, 3 x 10(-3) M). This inhibitory effect was antagonized by the NO precursor, L-arginine (3 x 10(-3) M). NG-nitro-D-arginine (10(-4) M) did not affect the relaxations to EFS. 5. Incubation with either the NO scavenger, oxyhaemoglobin (10(-5) M), or methylene blue (10(-5) M), an inhibitor of guanylate cyclase activation by NO, caused significant inhibitions of the EFS-evoked relaxations, and while oxyhaemoglobin abolished the relaxations to exogenously added NO (acidified sodium nitrite, 10(-6) - 10(-3) M), there still persisted a relaxation to NO of 24.4 +/- 5.1% (n = 6) in the presence of methylene blue. 6. Glibenclamide (3 x 10(-6) M), an inhibitor of ATP-activated K(+)-channels, did not alter the relaxations to either EFS-stimulation or NO, while the blocker of Ca(2+)-activated K(+)-channels, charybdotoxin (3 x 10(-8) M), caused a significant inhibition of both the electrically-induced relaxations and the relaxations to exogenously added NO. Furthermore, charybdotoxin blocked relaxations induced by the cell permeable analogue of cyclic GMP, 8-bromo cyclic GMP (8 Br-cyclic GMP). 7. These results suggest that relaxations of horse deep penile arteries induced by NANC nerve stimulation involve mainly NO or a NO-like substance from nitrergic nerves. NO would stimulate the accumulation of cyclic GMP followed by increases in the open probability of Ca(2+)-activated K(+)-channels and hyperpolarization leading to relaxation of horse penile arteries.

Vasoactive intestinal polypeptide and other preprovasoactive intestinal polypeptide-derived peptides in the female and male genital tract: localization, biosynthesis, and functional and clinical significance

Vasoactive intestinal polypeptide, a neuropeptide with wide distribution in the central and peripheral nervous system, has a broad spectrum of biologic actions. The demonstration of vasoactive intestinal polypeptide containing nerve fibers within the female and male genital tract 17 years ago indicated a putative role for this peptide in the local nervous control of reproductive functions. The genes encoding the preprovasoactive intestinal polypeptide precursor molecule and the vasoactive intestinal polypeptide receptor have been identified. The gene expression has been studied by the use of specific antibodies against the functional domains of the vasoactive intestinal polypeptide precursor and the biologic action elucidated by both in vivo and in vitro methods. Evidence has been provided to support vasoactive intestinal polypeptide as a neurotransmitter in several physiologic events in the genital tracts (i.e., blood flow and nonvascular smooth muscle relaxation). In the ovary vasoactive intestinal polypeptide seems to play an important role as regulator and/or modulator of folliculogenesis and steroidogenesis. In the male genital tract vasoactive intestinal polypeptide seems to participate in the control of erection. Vasoactive intestinal polypeptide has been suggested as a causative factor in some diseases of the genital organs (e.g., it may play a pathophysiologic role in male impotence and the peptide is currently used in the treatment of this condition). Vasoactive intestinal polypeptide may be important for control of the low resistance in the fetomaternal vascular bed and is therefore a putative factor involved in the development of preeclampsia. The therapeutic potential of vasoactive intestinal polypeptide and future agonists and antagonists will be revealed by ongoing and forthcoming studies.

Colocalization of vasoactive intestinal polypeptide and nitric oxide in penis-innervating neurons in the major pelvic ganglion of the rat

By using a combination of fluorescent retrograde labeling and double immunofluorescence histochemistry, the present study revealed in the rat that the vast majority of major pelvic ganglion neurons innervating penile erectile tissue contained both vasoactive intestinal polypeptide (VIP) and nitric oxide synthase. The result suggests that VIP and nitric oxide may exert a cooperative action in penile erection.

Fluparoxan in male erectile disorder: a case report

During a protocol study for the efficacy of fluparoxan (a noradrenergic α(2)-antagonist) in depression, a positive effect on male erectile impotence has been observed in one case, with no important secondary effects. This result confirms the involvement of α(2)-antagonists in the handling of male impotence. The action on the erectile disorder appeared slightly before the antidepressive effect (2-3 weeks) and lasted for 6 weeks after the discontinuation of treatment, suggesting that the effects on impotence were not a mere reflection of the antidepressive action.

Co-localization of nitric oxide synthase and vasoactive intestinal peptide immunoreactivity in neurons of the major pelvic ganglion projecting to the rat rectum and penis

Nitric oxide synthase (NOS)- and vasoactive intestinal peptide (VIP)-immunoreactive neurons projecting to the upper rectum or penis were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of male rats. Five days after injection of Fluoro-Gold (FG) into the upper rectum or penis, the major pelvic ganglion was treated with colchicine. FG injected into the upper rectum labelled many ganglion neurons in the major pelvic ganglion. Immunohistochemistry showed that 37% of FG-labelled neurons were immunoreactive for NOS and 33% for VIP. After injection of FG into the penis, 41% of FG-labelled neurons were immunoreactive for NOS and 25% for VIP. Serial cryostat sections stained for NOS and VIP, respectively, showed the co-localization of NOS and VIP in the ganglion cells projecting to the rectum and penis. In the major pelvic ganglion of the colchicine-treated animals, about 17% of the ganglion cells were immunoreactive for NOS and 32% were immunoreactive for VIP. These neurons were small in diameter (less than 30 microns). A histogram showing cell sizes in cross-sectional areas of NOS-immunoreactive neurons coincided with that of VIP-immunoreactive neurons. Most of the NOS- and VIP-immunoreactive neurons were less than 600 microns. These results indicate that small neurons containing both NOS and VIP in the major pelvic ganglion project to the rectum and penis. In the penile erectile tissues and enteric ganglia, NO and VIP may be released from the same axons and may act concomitantly on the target tissue.

Concentrations of vasoactive intestinal polypeptide in corpus cavernosum and peripheral venous blood during prostaglandin E1-induced erection

Vasoactive intestinal polypeptide (VIP) has been suggested to play a role as a nonadrenergic, noncholinergic neurotransmitter or neuromodulator involved in the process of erection. Until now, data about fluctuating concentrations of VIP in corpus cavernosum (CC) blood have been controversial. The present study describes a modified radioimmunoassay method that was developed in our laboratory for the determination of VIP in plasma. Examination of 12 patients suffering from impotentia coeundi (6 men with psychogenic impotence, 2 with induratio penis plastica, and 4 with impotence of vascular origin) showed that the concentrations of VIP in corpus cavernosum blood during pharmacologically induced erection did not increase in organically healthy men or in men with impotentia coeundi of vascular origin. The VIP concentrations in peripheral venous blood and those in CC blood were similar.

Drug-induced male sexual dysfunction. An update

Impotence, defined as the consistent inability to maintain an erect penis of sufficient rigidity for sexual intercourse, has been estimated to affect 10 million American men. An age dependence has been shown to exist, with 25% of men over age 65 affected. A large body of clinical experience and published reports in the literature link many commonly prescribed drugs with sexual dysfunction. Drugs can affect sexual function at a variety of points such as inhibition of ejaculation or sedation/depression leading to reduced libido. Antihypertensive drugs have been most commonly associated with impotence. There have been reports of sexual dysfunction with almost all classes of antipsychotics, but little clinical investigation has been performed. Other drugs associated with sexual dysfunction include digoxin, clofibrate, cimetidine and various hormonal agents and antineoplastics. An important first step in approaching all impotent patients is the taking of a detailed medical, surgical, sexual and drug/substance abuse history. The least invasive form of therapy should be employed. Recent studies have shown intracavernous injections of alprostadil (prostaglandin E1) to be safe and effective for long term use. Vacuum constriction devices may also be of help. Better and more durable prostheses are now available should other treatment be unsuccessful.

Inhibition of nerve stimulation-induced vasodilatation in corpora cavernosa of the pithed rat by blockade of nitric oxide synthase

1. The effect of inhibition of nitric oxide synthase by NG-nitro-L-arginine methyl ester (L-NAME) on nerve stimulation-induced vasodilation in corpora cavernosa was studied in the pithed rat. Corporal vasodilation was estimated by the increase in ratio (corpora cavernosal pressure/systemic blood pressure; CP/BP) following electrical stimulation of the sacral part of the spinal cord. 2. L-NAME (2, 5, 10 and 25 mg kg-1) caused an increase in BP and a dose-dependent inhibition of the rise in the CP/BP ratio following stimulation. 3. The inhibitory effect of L-NAME (25 mg kg-1) on the corporal response to spinal cord stimulation, as well as the pressor response, was partially prevented by prior administration of L- but not D-arginine (400 mg kg-1, i.v.). 4. L-NAME (20 mg kg-1, i.v.) did not inhibit the rise in corporal pressure resulting from direct intracavernosal administration of papaverine (400 micrograms over 2 min). However, this response was inhibited by 5-hydroxytryptamine (20 micrograms kg-1, i.v.). 5. The results are indicative of a role of nitric oxide (NO) in the corporal vasodilator response to erectile stimulation.

Vasointestinal polypeptide (VIP)-immunoreactive nerves in the boar penis

Vasointestinal polypeptide (VIP)-immunoreactivity was localized at LM-level in cryostat sections using a peroxidase-anti-peroxidase technique, and at EM-level in glutaraldehyde-fixed, resin-embedded sections using an immunogold technique, of samples from the penis of 3 Hampshire boars with a history of normal erection and mating behaviour. One boar of the same breed with an impotence diagnosis was also examined. In the normal animals, VIP-immunoreactivity was localized into nerves associated to blood vessels and non-vascular smooth muscle in the capsular lamina propria and the fibromuscular layers, and intermingled under the penis epithelium. At EM level, the immunogold localization confirmed the above mentioned results, VIP being localized in nerve terminals. Nerve terminals without VIP-reactivity had EM appearance of cholinergic or adrenergic nerve terminals. No obvious differences in VIP innervation were noticed among the normal boars. In the impotent animal, a marked depletion of VIP-immunoreactivity was evident, as well as degenerative changes in the adrenergic and cholinergic nerve profiles. It is concluded that the porcine penis is well innervated, along with adrenergic and cholinergic components, by VIP-containing nerves. The depletion of the scattered VIP-containing nerves in the impotent case suggests its involvement in the mechanisms of penile erection in the boar.

CGRP immunoreactivity and NADPH-diaphorase in afferent nerves of the rat penis

Calcitonin gene-related peptide (CGRP)-immunoreactive afferent nerve fibers are abundant in the rat penis. In addition, NADPH-diaphorase, which stains for nitric oxide synthase, has been localized within both autonomic and sensory dorsal root ganglia (DRG) and may be part of an important biochemical pathway involved in penile tumescence. The purpose of this study was: 1) to examine the circuitry of afferent nerves that are CGRP immunoreactive from the L6 DRG, 2) to examine the possibility that there are NADPH-diaphorase-positive afferent fibers from the L6 DRG to the rat penis, and 3) to examine the localization and colocalization of CGRP and NADPH-diaphorase within L6 DRG afferent perikarya. Calcitonin gene-related peptide immunostaining in the penis was eliminated following a bilateral transection of the pudendal nerves, but was unchanged following a bilateral transection of the pelvic splanchnic or hypogastric nerves. The NADPH-diaphorase staining was not altered by any of the nerve transections. Injection of the retrograde axonal tracer fluorogold (FG) into the dorsum penis labeled perikarya in the L6 DRG. Although the majority of FG-labeled perikarya contained neither CGRP nor NADPH-diaphorase, small subpopulations of perikarya contained either CGRP immunoreactivity, NADPH-diaphorase, or both. A unilateral pudendal nerve transection virtually eliminated (> 99%) FG labeling in the ipsilateral L6 DRG. These data suggest that NADPH-diaphorase and CGRP are present, either together or separately, within a subpopulation of penile afferent perikarya. In addition, CGRP-immunoreactive afferent nerve fibers reach the penis primarily via the pudendal nerves. Finally, NADPH-diaphorase-positive penile afferents may be another important source of nitric oxide (NO) for penile tumescence.

Vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM) in human penile corpus cavernosum tissue and circumflex veins: localization and in vitro effects

Localization and functional effects of vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM), two peptides derived from a common precursor molecule, were investigated in isolated preparations from human penile corpus cavernosum (CC) and circumflex vein (CV). VIP- and PHM-immunoreactivity (IR) was demonstrated in both CC and CV. The concentrations of VIP-IR and PHM-IR in CC tissue were 54.4 +/- 15.3, and 42.0 +/- 7.5 pmol g-1 wet weight respectively with a VIP/PHM ratio of 1.5 +/- 0.4 (mean +/- SEM). The corresponding values for CV tissues were 28.0 +/- 7.7 and 9.6 +/- 2.6 pmol g-1 wet weight with a VIP/PHM ratio of 3.1 +/- 0.4. CC and CV displayed VIP- and PHM-IR confined to nerve fibres in close relation to bundles of smooth muscle cells and blood vessels in both tissues. In vitro, VIP and PHM had no effects in unstimulated tissue preparations. Both peptides concentration-dependently (10(-9)-10(-6) M) relaxed CC and CV preparations precontracted with 3 x 10(-6) M noradrenaline. In CC the maximum relaxant effect of VIP and PHM was 22 +/- 11% and 9 +/- 9% and in CV the corresponding values were 82 +/- 8% and 93 +/- 3% respectively. The present study supports the hypothesis of VIP and PHM as neurotransmitters and/or neuromodulators in the nervous control of penile erection.

The human penis: an unusual penetration of NPY-immunoreactive nerves within the medial muscle coat of the deep dorsal vein

The deep dorsal penile vein was obtained from seven patients undergoing surgery for erectile dysfunction. The veins were studied histologically and immunohistochemically for serotonin, dopamine beta-hydroxylase, vasoactive intestinal polypeptide, neuropeptide Y, substance P, calcitonin gene-related peptide, somatostatin, and [Leu]- and [Met]enkephalin. Histologically, the deep dorsal vein was found to be a large muscular vein with a thin endothelial lining. The tunica media was composed of an inner longitudinally and an outer circularly arranged smooth muscle layer. Numerous vasa vasorum (up to 30 in a single transverse section) were found in the tunica adventitia. The greatest density of nerves supplying the deep dorsal vein and vasa vasorum were neuropeptide Y-immunoreactive nerves followed (in a decreasing order) by vasoactive intestinal polypeptide- and dopamine beta-hydroxylase-immunoreactive nerves. Substance P-, calcitonin gene-related peptide- and somatostatin-immunoreactive nerves, but not serotonin-, [Leu]- and [Met]enkephalin-immunoreactive nerves, were occasionally found around the deep dorsal vein. All these nerve fibers were confined to the adventitial-medial border except neuropeptide Y-immunoreactive nerves which in addition penetrated the tunica media to the subendothelial layer of the deep dorsal vein. In contrast, neuropeptide Y-immunoreactive nerves supplying the vasa vasorum were always confined to the adventitial-medial border. The possible function of the medial innervation of the deep dorsal vein by neuropeptide Y-immunoreactive nerves is discussed.

Effects of pinacidil upon penile erectile tissue, in vitro and in vivo

The effect of pinacidil, a new antihypertensive vasodilator, was studied in vitro upon human and porcine Corpus cavernosum and in vivo upon simian Corpus cavernosum. In vitro, pinacidil incubation (10(-5)-10(-3) M) was found to induce a concentration-dependent inhibition of the tissue response to norepinephrine (NE) and high potassium (K+). Likewise a concentration-related relaxation of the tissue, precontracted with either NE or K+, was seen using pinacidil 10(-5)-10(-3) M. Depending on the concentration applied, spontaneous activity as well as tone and amplitude of the contractions were reduced until total relaxation of the tissue was obtained with a pinacidil incubation of 10(-3) M. In vivo, 5 mg pinacidil in 0.3 ml solution was injected intracavernosally in 17 monkeys. Sixteen monkeys developed tumescence and 10, rigidity of the penis as well. Only one of 5 showed a decrease in the systemic blood pressure. Pinacidil might be of clinical interest as an agent facilitating erection when given intravernosally.

A clinical trial of intracavernous vasoactive intestinal peptide to induce penile erection

A double-blind, placebo-controlled clinical trial of the intracavernous injection of vasoactive intestinal peptide was conducted and studied in 24 men with erectile dysfunction of diabetic, neurogenic and psychogenic etiology. The patients were randomized into 6 groups of 4 subjects each and received either placebo, or 200 or 400 pmol. vasoactive intestinal peptide at each of 3 consecutive weekly visits. An increase in penile length was associated significantly with treatment (F equals 5.10, p equals 0.01), dose-related, and independent of the time and sequence of treatment. An increase in penile diameter was associated significantly with treatment (F equals 8.14, p equals 0.001) and time (F equals 8.14, p equals 0.001), dose-related and independent of the sequence of treatment. Penile rigidity was associated significantly with time (F equals 5.44, p equals 0.008), associated nearly significantly with treatment (F equals 3.11, p equals 0.056) and independent of sequence of treatment. Despite some measurable treatment-related increase none of the patients achieved penile rigidity adequate for intromission.

Local and systemic effects of chronic intracavernous injection of papaverine, prostaglandin E1, and saline in primates

To compare the local and systemic effects of chronic intracavernous injection of papaverine, prostaglandin E1, and saline on erectile tissue, eight pigtail monkeys underwent 75 injections over a nine-month period. Monkeys were divided into three groups; each group received papaverine (10 mg.), prostaglandin E1 (20 micrograms.), or saline (one ml.). The erectile response was closely observed for two hours after each injection to monitor the onset, degree, and duration of erection. Liver function tests were performed every three months to detect early systemic metabolic changes. After sacrifice, the simian penises were perfused in situ and examined histologically with both light and electron microscopy. Papaverine resulted in an initially strong erectile response, but this was maintained throughout the length of the study in only two monkeys. In contrast, prostaglandin E1 resulted in tumescence that was maintained in all monkeys over the nine-month period. In addition, the papaverine group had elevated liver enzymes and significant histologic changes with loss of normal architecture on both light and electron microscopy. The other two groups showed only minimal histologic changes or none.

VIP and autonomic neurotransmission

A variety of peptides have been proposed as transmitter candidates in non-cholinergic, non-adrenergic nerves. The nerves containing vasoactive intestinal polypeptide (VIP), which innervate blood vessels, non-vascular smooth muscle, mucosal epithelium and glands comprise a major and wide-spread population of the peptide-containing systems. There is now experimental data supporting the view that VIP is a transmitter in non-adrenergic, non-cholinergic nerves in the digestive tract, respiratory tract and urogenital tract, controlling smooth muscle tone and motility, blood flow and secretion. It is possible that impairment of VIP-containing nerves is involved in a number of autonomic dysfunctions.

Evaluation and management of erectile dysfunction

The man who seeks treatment for impotence typically has a sense of inadequacy that extends beyond sexual satisfaction to his business and personal relationships. Although no magic potion is available, current medical technology allows the surgeon to accommodate each patient who seeks treatment, guaranteeing sufficient penile rigidity to effect coitus.

Applications of microsurgery in urology

The applications of microsurgery in urology have increased in the decade since urologists first used such techniques. The primary uses for microsurgery in urology at first were vasovasostomy, vasoepididymostomy, and testicular autotransplantation. Penile revascularization has recently become another procedure for which microsurgery is used with increasing frequency. As more urologists learn the techniques, other urologic applications for microsurgery surely will develop.

Fundamentals and hemodynamics of penile erection

Human penile erection is a complex phenomenon mediated through the coordinated interaction among the nervous, vascular, and musculosystems. For social and ethical reasons, the mechanism and hemodynamics of this essential human function remained speculative and controversial for many years. In the past decade, however, advances in technology, together with a marked increase in clinical and research activity, have resolved some of the controversy and have provided a better understanding of erectile physiology. In this essay, we will review traditional concepts, as well as the new and exciting findings from many different research centers, concerning the physiologic mechanisms of penile erection that involves the arterial, venous, and nervous systems.

Pharmacology of penile erection in humans

The pharmacologic aspects of erection, including neuropharmacology and erectile responses to exogenous agents, are reviewed. The pharmacology of erection is complex and still incompletely understood. Older evidence suggesting acetylcholine as the primary neurotransmitter has been shown to be insufficient. Our recent experiments utilizing strips of human corpus cavernosum indicate the need to consider the roles of other erectogenic substances, such as vasoactive intestinal polypeptide, endothelium-derived relaxation factor (EDRF), and prostaglandins. From the results of these studies, three stages in the development of an erection are postulated: (1) withdrawal of alpha-adrenergic neuromuscular activity, (2) inhibition of alpha-adrenergic neuromuscular activity by endogenous substances such as prostaglandin E1 and vasoactive intestinal polypeptide, and (3) activation of NANC neurotransmission and direct relaxation of smooth muscle by endogenous substances such as EDRF.

Autoradiographic evidence of muscarinic cholinergic receptors in the corpora cavernosa penis of the rat

Recent studies have questioned the role of acetylcholine in the physiology of penile erectile tissue. The responsiveness of penile erectile tissue to acetylcholine would depend, in part, on the presence of cholinergic receptors on the smooth muscle. The specific binding of [3H]quinuclidinyl benzilate (QNB) to cholinergic receptors in sections of penile crura of the rat was analyzed by in vitro neurotransmitter autoradiography. Silver grain density measurements indicated that muscarinic cholinergic receptor binding sites are located almost entirely over the corpora cavernosa penis. Virtually no specific [3H]QNB binding was present in the tunica albuginea or adjacent skeletal muscle tissue. Within the erectile tissue, specific binding occurred both over the columns of intrinsic smooth muscle which form the walls of the cavernous spaces and around the more distal branches of the penile arteries. The high concentration of muscarinic cholinergic receptors in the corpora cavernosa penis is consistent with the suggestion that acetylcholine has an important, albeit undefined role in the function of penile erectile tissue.

Responses of smooth muscle strips from penile erectile tissue to drugs and transmural nerve stimulation

1. The mechanical response to drugs and to electrical stimulation of nerves was investigated in isolated strips of intrinsic smooth muscle from the corpora cavernosa penis of the rat. 2. Noradrenaline caused muscle strips to contract in a dose-dependent manner. Contractions could be blocked by pretreatment with the alpha-adrenoreceptor antagonist, phentolamine. 3. Acetylcholine and carbachol had no effect on the baseline tension of muscle strips. Both drugs were relatively ineffective in relaxing noradrenaline-contracted strips. 4. Field stimulation of isolated muscle strips elicited contractions which were blocked by tetrodotoxin and greatly attenuated with phentolamine or reserpine pretreatment. Acetylcholine inhibited the excitatory response to field stimulation. This inhibitory effect of acetylcholine could be blocked with atropine. 5. Field stimulation of noradrenaline-contracted muscle strips caused relaxation. This inhibitory effect, due to nerves which arise from the pelvic plexus, is unaffected by substances which act on cholinergic systems. 6. The results suggest that the erectile muscle of the rat is similar to that of man in that it receives an excitatory noradrenergic innervation and an inhibitory innervation which may have a non-cholinergic component. Although acetylcholine may have a role in penile physiology of the rat, it is unlikely that it has a postsynaptic action.

The role of vasoactive intestinal polypeptide as a neurotransmitter in canine penile erection: a combined in vivo and immunohistochemical study

Vasoactive intestinal polypeptide (VIP), a 28-amino-acid polypeptide found in the human gut and genitourinary tract, primarily affects vasodilation and smooth-muscle relaxation. These effects have led to speculation that this neuropeptide may be a neurotransmitter in certain bodily functions, such as penile erection. We therefore designed an in vivo animal model to elucidate the influence of VIP and VIP antibody on the different stages of penile erection. We also performed immunohistochemical studies of the penile tissue to obtain further information about the distribution of VIP in the corpora cavernosa. Intracavernous injection of VIP induced penile erection. Its effect on arterial inflow was minor, but it caused active venous outflow restriction and was important in maintaining erection. VIP antibody blocked venous outflow restriction during neurostimulation-induced erection. VIP was found in the cavernous tissue (in the area between the smooth-muscle cells and the sinusoidal spaces) in close proximity to the arteries. We conclude that VIP is a neurotransmitter in the erectile tissue of the penis, and that its effects are similar to those from electrostimulation of the cavernous nerve. VIP increases arterial flow, decreases venous flow, and induces sinusoidal relaxation.

Changes in the VIPergic, cholinergic and adrenergic innervation of human penile tissue in diabetic and non-diabetic impotent males

Penile tissue (consisting of corpus cavernosum and tunica albuginea) was obtained from 19 patients undergoing surgery for the implantation of penile prostheses. The tissue was examined for vasoactive intestinal polypeptide-like immunoreactivity in nerves, acetylcholinesterase-positive staining in nerves and noradrenaline content. Impotence was due to a variety of causes; 11 patients were classified as a 'non-neuropathic' group on the basis of their clinical history which included Peyronie's disease, vascular disease, hypertension and psychogenic impotence. Vasoactive intestinal polypeptide-like immunoreactive and acetylcholinesterase-positive nerves were present and the pattern and distribution were similar in each patient in this group. The noradrenaline content of the tunica albuginea was significantly lower than the corpus cavernosum (p less than 0.02), although there was a linear relationship between the noradrenaline contents of the two regions (r = 0.95, p less than 0.01). By comparison, a complete absence of vasoactive intestinal polypeptide-like immunoreactivity in nerves was observed in a patient with a cauda equina lesion. Five out of six diabetic patients studied revealed a marked reduction in vasoactive intestinal polypeptide-like immunoreactivity in nerves associated with the cavernous smooth muscle, while acetylcholinesterase-positive staining was reduced in three out of five diabetic patients studied. The noradrenaline content of the corpus cavernosum from diabetic patients was significantly lower (p less than 0.02) than that of the 'non-neuropathic' group. The noradrenaline content of the tunica albuginea, however, was similar in both groups. The results provide evidence that VIPergic, cholinergic and adrenergic nerves in the penis are affected in diabetes mellitus and thus may contribute to the development of impotence in diabetic patients.

Intracavernous self-injection with phentolamine and papaverine for the treatment of impotence

To evaluate the efficacy and safety of intracavernous self-injection of phentolamine and papaverine for the treatment of impotence, 30 patients were enrolled in a prospective, randomized, double-blind, placebo-controlled cross-over study of papaverine and phentolamine versus normal saline. A total of 29 patients completed the study. The phentolamine plus papaverine combination resulted in erection in 24 patients (82.8 per cent) and no erection occurred after injection of saline. Of the patients 12 (41.4 per cent) experienced technical difficulties with the injection. Ecchymosis of the penis at the site of injection was common and 1 patient experienced priapism that resolved spontaneously. No other side effects occurred. Intracavernous self-injection with phentolamine and papaverine appears to be a safe and effective treatment of impotence but long-term effects must be determined.

Vasoactive intestinal polypeptide levels and distribution in the penis of old rats

Vasoactive intestinal polypeptide (VIP) levels and distribution were studied in the penis of young-adult (3-month-old) and old (30-month-old) Wistar rats by radioimmunoassay and immunofluorescence. No significant changes in tissue VIP concentrations or distribution occurred in the penis of old rats compared to young-adult rats. The present data indicate that the age-related impairment of male sexual function is not dependent on modifications of the VIP-ergic innervation of penile tissue.