Nitric oxide mediates neurogenic relaxation induced in rabbit cavernous smooth muscle by electric field stimulation

Role of a novel tetrodotoxin-resistant sodium channel in the nitrergic relaxation of corpus cavernosum from the South American rattlesnake Crotalus durissus terrificus

INTRODUCTION

Coitus in snakes may last up to 28 hours; however, the mechanisms involved are unknown.

AIM

To evaluate the relevance of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) system in snake corpus cavernosum reactivity.

METHODS

Hemipenes were removed from anesthetized South American rattlesnakes (Crotalus durissus terrificus) and studied by light and scanning electronic microscopy. Isolated Crotalus corpora cavernosa (CCC) were dissected from the non-spiny region of the hemipenises, and tissue reactivity was assessed in organ baths.

MAIN OUTCOME MEASURES

Cumulative concentration-response curves were constructed for acetylcholine (ACh), sodium nitroprusside (SNP), 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine (BAY 41-2272), and tadalafil in CCC precontracted with phenylephrine. Relaxation induced by electrical field stimulation (EFS) was also done in the absence and presence of N(ω) nitro-L-arginine methyl ester (L-NAME; 100 µM), 1H-[1, 2, 4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 µM) and tetrodotoxin (TTX; 1 µM).

RESULTS

The hemipenes consisted of two functionally concentric corpora cavernosa, one of them containing radiating bundles of smooth muscle fibers (confirmed by α-actin immunostaining). Endothelial and neural nitric oxide synthases were present in the endothelium and neural structures, respectively; whereas soluble guanylate cyclase and PDE5 were expressed in trabecular smooth muscle. ACh and SNP relaxed isolated CCC, with the relaxations being markedly reduced by L-NAME and ODQ, respectively. BAY 41-2272 and tadalafil caused sustained relaxations with potency (pEC(50) ) values of 5.84 ± 0.17 and 5.10 ± 0.08 (N=3-4), respectively. In precontracted CCC, EFS caused frequency-dependent relaxations that lasted three times longer than those in mammalian CC. Although these relaxations were almost abolished by either L-NAME or ODQ, they were unaffected by TTX. In contrast, EFS-induced relaxations in marmoset CC were abolished by TTX.

CONCLUSIONS

Rattlesnake CC relaxation is mediated by the NO-cGMP-PDE5 pathway in a manner similar to mammals. The novel TTX-resistant Na channel identified here may be responsible for the slow response of smooth muscle following nerve stimulation and could explain the extraordinary duration of snake coitus.

Effects of ethanol on the tonicity of corporal tissue and the intracellular Ca2+ concentration of human corporal smooth muscle cells

Heavy alcohol consumption is associated with an increased risk of erectile dysfunction (ED); however, the acute effects of ethanol (EtOH) on penile tissue are not fully understood. We sought to investigate the effects of EtOH on corporal tissue tonicity, as well as the intracellular Ca(2+) concentration ([Ca(2+)](i)) and potassium channel activity of corporal smooth muscle. Strips of corpus cavernosum (CC) from rabbits were mounted in organ baths for isometric tension studies. Electrical field stimulation (EFS) was applied to strips precontracted with 10 μmol L(-1) phenylephrine as a control. EtOH was then added to the organ bath and incubated before EFS. The [Ca(2+)](i) levels were monitored by the ratio of fura-2 fluorescence intensities using the fura-2 loading method. Single-channel and whole-cell currents were recorded by the conventional patch-clamp technique in short-term cultured smooth muscle cells from human CC tissue. The corpus cavernosal relaxant response of EFS was decreased in proportion to the concentration of EtOH. EtOH induced a sustained increase in [Ca(2+)](i) in a dose-dependent manner, Extracellular application of EtOH significantly increased whole-cell K(+) currents in a concentration-dependent manner (P < 0.05). EtOH also increased the open probability in cell-attached patches; however, in inside-out patches, the application of EtOH to the intracellular aspect of the patches induced slight inhibition of Ca(2+)-activated potassium channel (KCa) activity. EtOH caused a dose-dependent increase in cavernosal tension by alterations to [Ca(2+)](i). Although EtOH did not affect KCa channels directly, it increased the channel activity by increasing [Ca(2+)](i). The increased corpus cavernosal tone caused by EtOH might be one of the mechanisms of ED after heavy drinking.

Nicotine potentiates the nitrergic relaxation responses of rabbit corpus cavernosum tissue via nicotinic acetylcholine receptors

The presence of neuronal nicotinic acetylcholine receptors in rabbit corpus cavernosum tissue and possible mechanisms underlying the potentiation of electrical field stimulation induced relaxation by nicotine were analyzed. In corpus cavernosum tissue strips nicotine (3 x 10(-5) M) and acetylcholine (10(-3) M) produced potentiation on electrical field stimulation (amplitude 50 V; frequency 4 Hz; width 0.8 ms) induced relaxation responses. This nicotine-induced potentiation was not altered by atropine (10(-6) M), guanethidine (5 x 10(-6) M) and indomethacin (10(-5) M), but abolished by hexamethonium chloride (10(-5) M) and L-nitro arginine methyl ester (10(-5) M). Nicotine did not cause any alteration on a single dose of carbachol (3 x 10(-5) M) and sodium nitroprusside (10(-5) M) induced relaxation responses. The results suggest that, nicotine-induced potentiation is NO and nicotinic acetylcholine receptor dependent but independent from prostaglandin synthesis, activation of muscarinic receptors and does not require intact adrenergic neurons. Nicotine did not affect smooth muscle and endothelium directly. In conclusion, in this study we showed for the first time that, nicotine acts on the nicotinic acetylcholine receptors located on the nitrergic nerves, thereby evoking the release of NO from these nerve terminals inducing relaxation response in rabbit corpus cavernosum tissue.

Effect of microcurrent electrical tissue stimulation on equine tenocytes in culture

OBJECTIVE

To determine effects of microcurrent electrical tissue stimulation (METS) on equine tenocytes cultured from the superficial digital flexor tendon (SDFT).

SAMPLE POPULATION

SDFTs were collected from 20 horses at slaughter.

PROCEDURE

Tenocytes were isolated following outgrowth from explants and grown in 48-well plates. Four methods of delivering current to the tenocytes with a METS device were tested. Once the optimal method was selected, current consisting of 0 (negative control), 0.05, 0.1, 0.5, 1.0, or 1.5 mA was applied to cells (8 wells/current intensity) once daily for 8 minutes. Cells were treated for 1, 2, or 3 days. Cell proliferation, DNA content, protein content, and apoptosis rate were determined.

RESULTS

Application of microcurrent of moderate intensity increased cell proliferation and DNA content, with greater increases with multiple versus single application. Application of microcurrent of moderate intensity once or twice increased protein content, but application 3 times decreased protein content. Application of current a single time did not significantly alter apoptosis rate; however, application twice or 3 times resulted in significant increases in apoptosis rate, and there were significant linear (second order) correlations between current intensity and apoptosis rate when current was applied twice or 3 times.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study indicate that microcurrent affects the behavior of equine tenocytes in culture, but that effects may be negative or positive depending on current intensity and number of applications. Therefore, results are far from conclusive with respect to the suitability of using METS to promote tendon healing in horses.

Influence of electrode placement on effective field strength in the superficial digital flexor tendon of horses

OBJECTIVE

To determine the relationship between the output of an electrical treatment device and the effective field strength in the superficial digital flexor tendon of horses.

SAMPLE POPULATION

Cadaver horse forelimbs without visible defects (n = 8) and 1 live pony.

PROCEDURE

Microcurrents were generated by a microcurrent electrical therapy device and applied in proximodistal, dorsopalmar, and mediolateral directions in the entire forelimbs, dissected tendons, and the pony with various output settings. Corresponding field strengths in the tendons were measured.

RESULTS

A linear relationship was detected between current and field strength in all conditions and in all 3 directions. In dissected tendons, significant differences were detected among all 3 directions, with highest field strength in the proximodistal direction and lowest in the dorsopalmar direction. In the entire forelimbs, field strength in the proximodistal direction was significantly lower than in the mediolateral direction. Results in the pony were similar to those in the entire forelimbs.

CONCLUSIONS AND CLINICAL RELEVANCE

Electrode placement significantly affected field strength in the target tissue. Many surrounding structures caused considerable reduction of field strength in the target tissue. These factors should be taken into account when establishing protocols for electrical current-based therapeutic devices if these devices are proven clinically effective.

Endothelial function in patients with vasculogenic erectile dysfunction

OBJECTIVES

Erectile dysfunction (ED) commonly coexists with coronary artery disease (CAD) and/or risk factors for atherosclerosis. Because the silent or documented atherosclerosis or vascular risk factors are very frequent, the possibility of endothelial dysfunction in ED patients is expected to be increased. Our aim was to evaluate the endothelial functions in patients with vasculogenic ED with vascular risk factors and compare them with age-matched non-ED patients or healthy controls.

DESIGN

We studied 36 patients with presumed vasculogenic ED, 39 age-matched patients with similar risk factors without ED and 25 age-matched healthy controls without ED, known cardiovascular disease or risk factors. Erectile function was evaluated by the International Index of Erectile Dysfunction (IIEF) scores. Brachial artery flow-mediated dilatation (FMD) and nitroglycerine-mediated dilatation (NMD) were measured.

RESULTS

Baseline demographics were similar except the IIEF score and duration of diabetes in patients with ED. Brachial artery FMD and NMD were significantly reduced in patients with ED (3.2+/-3. vs. 6+/-4, p<0.0001 for FMD, 12.2+/-6 vs. 15.4+/-6 p=0.032 for NMD). In patients with similar risk factors but without ED, FMD was significantly lower but NMD were not different compared with healthy controls (6+/-4 vs. 10.2+/-3, p<0.0001 for FMD and 15.4+/-8 vs. 16.4+/-6, p=0.81). IIEF scores were weakly correlated with FMD (r=0.25, p=0.028) in patients with ED. There were significant correlations between FMD and NMD in patients with ED (r=0.46, p=0.05) and with risk factors (r=0.72, p<0.0001) but not in healthy controls (r=0.54, p=0.792). Vasculogenic ED patients have more markedly impaired endothelial and smooth muscle functions compared with patients with similar risk factors but no ED.

Intracavernous Sodium Nitroprusside (SNP) versus Papaverine/Phentolamine in Erectile Dysfunction: A Comparative Study of Short‐Term Efficacy and Side‐Effects

OBJECTIVE

The aim of our work is to evaluate the efficacy of intracavernous sodium nitroprusside (SNP) in management of erectile dysfunction (ED) in a clinical comparative study with papaverine/phentolamine in ED patients.

METHODS

The study included 40 patients with ED divided into two groups. Group I include 20 patients receiving intracavernous (30 mg papaverine + 1 mg phentolamine) followed 1 week later by intracavernous 300 microg SNP. Group II included 20 patients receiving the same regimen of group I but with intracavernous SNP first followed by papaverine/phentolamine 1 week later. All patients were assessed clinically for their response and any developing complications.

RESULTS

The numbers of good and poor responders were not statistically significant (P > 0.05) among the two groups. The mean erectile duration of SNP was similar to bimix (P > 0.05). No side-effects whether local or systemic occurred with SNP while priapism and local penile pain were recorded with bimix solution.

CONCLUSIONS

Intracavernous pharmacotherapy is still a reliable method both for diagnosis and for treatment of ED. While preliminary results of our study show a potential of SNP to be an effective and safe intracavernous agent, long-term self-injection clinical trials are needed before large-scale usage is recommended.

Relaxation of rabbit corpus cavernosum by selective activators of voltage-gated sodium channels: role of nitric oxide-cyclic guanosine monophosphate pathway

OBJECTIVES

To investigate the capacity of voltage-gated Na(+) channel activators such as batrachotoxin, aconitine, veratridine, Ts1 (formerly Tityus gamma-toxin), and brevetoxin-3 to induce relaxation of rabbit isolated corpus cavernosum (RbCC) and the pharmacologic mechanisms underlying this phenomenon. The voltage-gated Na(+) channels of the corpus cavernosum are essential for erectile function. A number of biologic toxins exert their effects by modifying the properties of these channels.

METHODS

Male New Zealand white rabbits were anesthetized with pentobarbital sodium. Strips of RbCC were transferred to 10-mL organ baths containing oxygenated and warmed Krebs solution. The RbCC strips were connected to force-displacement transducers, and changes in isometric force were recorded using a PowerLab 400 data acquisition system. Corporeal smooth muscle was precontracted submaximally with phenylephrine (10 micromol/L).

RESULTS

The binding site-2 (batrachotoxin, aconitine, and veratridine) and binding site-5 (brevetoxin-3) voltage-gated Na(+) channel activators caused slow-onset RbCC relaxations, and the binding site-4 activator Ts1 produced transitory relaxations followed by a return to baseline. The Na(+)channel blockers tetrodotoxin and saxitoxin (0.1 micromol/L each) abolished the relaxations induced by these agonists. Similarly, the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine methyl ester (100 micromol/L) markedly reduced the relaxations and l-arginine (1 mmol/L) restored the relaxations. The soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxidiazolo[4,3-alpha] quinoxalin-1-one (10 micromol/L) reduced the relaxations, and the phosphodiesterase type 5 inhibitor sildenafil (100 nmol/L) significantly potentiated the relaxations by all activators.

CONCLUSIONS

Our results indicate that the relaxations evoked by selective activators of voltage-gated Na(+) channels are mediated by the release of nitric oxide from nitrergic nerves and the activation of the nitric oxide-cyclic guanosine monophosphate pathway in the smooth muscle cells of erectile tissue.

Activation of signal-transduction mechanisms may underlie the therapeutic effects of an applied electric field

Successful treatment of various medical complaints with an applied electric field has been reported over the years. The identities of the cellular mechanisms that are influenced by this type of treatment and facilitate the positive effects, remain elusive. A study of many in vitro and in vivo reports revealed that the beneficial effects can be attributed to the activation of membrane proteins, and specifically proteins involved in signal-transduction mechanisms. Not only may the proteins be affected but it is now well established that enhanced Ca(2+)influx, observed to follow electric stimulation of cells, also contributes to many calcium-dependent cellular processes which can be linked to the therapeutic effects discussed in this paper. An hypothesis of the physical changes caused by an applied, relatively small (10(3)to 10(4)V m(-1)range), electric field with low to moderate frequency (below 150 Hz), is postulated.

Effects of sildenafil citrate, acetylcholine, and sodium nitroprusside on the relaxation of rabbit cavernosal tissue in vitro

OBJECTIVES

To investigate the effect of sildenafil together with the influence of sodium nitroprusside and acetylcholine and further discuss its mechanism of action in vitro.

METHODS

Isolated strips of rabbit corpus cavernosum were stimulated isometrically with phenylephrine. Graded relaxations were induced using increasing concentrations of acetylcholine, sodium nitroprusside, and sildenafil alone and in combination.

RESULTS

The agents all relaxed the rabbit corpus cavernosal strips in a dose-dependent manner. The inhibitory potentials of the test agents were ranked (from least inhibitory to most inhibitory) as follows: sildenafil, acetylcholine plus sildenafil, sodium nitroprusside, sodium nitroprusside plus sildenafil, acetylcholine. The presence of sodium nitroprusside in the medium reduced the median effective dose for the sildenafil-induced relaxation of the cavernosal tissue from 3.65 x 10(-5) M to 2.73 x 10(-7) M, and the presence of acetylcholine reduced it to 9.79 x 10(-6) M.

CONCLUSIONS

Sildenafil enhances the relaxing effect of both sodium nitroprusside and acetylcholine on the phenylephrine-induced contraction of rabbit cavernosal tissue.

Nonadrenergic, noncholinergic relaxation of human isolated corpus cavernosum induced by scorpion venom

OBJECTIVES

To examine the effects of Tityus serrulatus scorpion venom (TSV) on human corpus cavernosum (HCC) using a bioassay cascade. Priapism is occasionally observed in scorpion envenomation, mostly in children.

METHODS

HCC strips were suspended in a cascade system and superfused with aerated and warmed Krebs' solution at 5 mL/min. Noradrenaline (3 micromol/L) was infused to induce a submaximal contraction of the HCC strips. The release of cyclooxygenase products was prevented by infusing indomethacin (6 micromol/L).

RESULTS

N(omega)-nitro-L-arginine methyl ester (10 micromol/L; n = 10) increased the tone of the preparations and significantly reduced (P <0.01) the acetylcholine (ACh) and TSV-induced relaxations. Subsequent infusion of L-arginine (300 micromol/L) partially reversed the increased tone and significantly restored the relaxations induced by TSV and ACh (P <0.01). The soluble guanylyl cyclase inhibitor ODQ (10 micromol/L; n = 8) markedly reduced (P <0.01) the relaxations induced by TSV, ACh, glyceryl trinitrate, and bradykinin. 7-Nitroindazole (10 micromol/L; n = 8) inhibited the relaxations induced by TSV by 84% (P <0.01) and also caused small, but significant, reductions in the ACh and bradykinin-induced HCC relaxations (P <0.05). Atropine (1 micromol/L; n = 6) abolished the relaxations evoked by ACh (P <0.01), but had no effect on those elicited by TSV. Tetrodotoxin (1 micromol/L; n = 6) abolished the relaxations induced by TSV (P <0.01) and also reversed the established TSV-induced relaxation (n = 4).

CONCLUSIONS

Our results indicate that TSV relaxes HCC through the release of nitric oxide from nonadrenergic, noncholinergic (NANC) nerves. The elucidation of the mechanism responsible for the TSV-induced relaxations might be useful for a better understanding of the development of priapism in cases of scorpion envenomation.

A standardized procedure for using human corpus cavernosum strips to evaluate drug activity

The main problem of using human corpus cavernosum (HCC) tissue to perform bioassay is linked to its limited availability further complicated by the heterogeneous source of the tissues used. Here, we show that gender reassignment is a reliable source of human tissue without major ethical problems. Indeed, the entire corpus cavernosum is obtained from the surgery procedure, which allows creating a standardized procedure to prepare HCC strip. In addition, human tissue, if kept in the fridge in the condition described, does not loose its ability to contract to phenylephrine (PE; alpha agonist), angiotensin II (AG II) and KCl up to 4 days. Furthermore, once contracted with PE, HCC relaxes to acetylcholine (endothelium-dependent mechanism); sodium nitroprusside (endothelium-independent mechanism); cromakalim (CRK), a K(ATP) channel opener; or alprostadil, a synthetic PGE2 (ALPR). In conclusion, we have standardized a procedure that allows the use of HCC strips to evaluate drug activity and/or to study pathophysiological mechanisms with an intact functional human tissue up to 4 days from the surgery procedure.

Does diabetes mellitus affect the progress of tolerance to isosorbide dinitrate (ISDN) in corporal tissue?

For erection to take place, the penile arteries and sinusoids have to dilate, thereby increasing the blood flow into the penis. There is increasing evidence that release of l-arginine derived nitric oxide (NO) from nonadrenergic-noncholinergic (NANC) nerves and from the sinusoidal endothelium is a major event in penile smooth muscle relaxation and promotes the endogenous formation of cyclic guanosine monophosphate (cGMP). Nitrovasodilators can be attributed to the activation of soluble guanylate cyclase, resulting in an increase in intracellular level of cyclic guanosine monophosphate, but prolonged exposure to high levels of nitroglycerine and other organic nitroesters induces tolerance against the cardiovascular effect. In this study, the aim was to determine the effect of diabetes on the corporal smooth muscle relaxant effect of ISDN and the effect of diabetes on the process of tolerance to the drug. For this purpose, alloxan-induced diabetic rabbits were used to form diabetes group. The responses of the corpus cavernous strips obtained from control and alloxan-induced diabetic rabbit were studied in organ chamber. In conclusion, prolonged in vitro exposure of corpus cavernosum strips obtained from control and diabetic groups to high concentrations of ISDN caused significant desensitization to the relaxant effect the drug. So, prolonged exposure of corporal tissue to the agents like nitroglycerine, used for treatment of impotence, may render ineffective the therapy in diabetic erectile impotence. However, intolerance to nitric oxide provides a rationale for the concept of using nitro oxide agents (like SNP) in the treatment of diabetic erectile dysfunction.

The molecular basis of penile erection

Over the past two decades our understanding of the physiology and the various mediators involved in the pathway of penile erection has greatly increased. This has enabled us to develop effective pharmacological treatments for ED.

Innervation of the fibro-elastic type of the penis: an immunohistochemical study in the male pig

The occurrence and colocalization of several biologically active neuropeptides, catecholamine-, acetylcholine- or nitric oxide-synthesizing enzymes-tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H), choline acetyl-transferase (ChAT) and nitric oxide synthase (NOS I), respectively, as well as the vesicular acetylcholine transporter (VAChT) were investigated in the penile glans (GP), corpus and crura (CP), as well as in the retractor penis muscle (RPM) of juvenile and adult boars. Immunohistochemistry revealed that nerves immunoreactive (IR) to TH, D beta H, vasoactive intestinal polypeptide (VIP) and somatostatin (SOM) were the most numerous, followed (in decreasing order of density) by nerves IR to NOS, neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), Leu5-enkephalin (LENK) and ChAT/VAChT. The CP contained the largest number of nerve fibres followed by the RPM, GP and corpus. Enzyme/peptide-containing nerves were associated with both the vascular and non-vascular penile structures. However, differences existed for their density and intrapenile distribution. Nerve terminals IR for different combinations of VIP, GAL or SOM were more frequent than those IR for NOS or CGRP in the non-vascular penile structures while the vasculature and the RPM received a prominent TH/D beta H-, VIP-, SOM- or NOS-IR nerve input. The present data indicate that the porcine penis receives nerve fibres that exhibit diverse chemical codes and that differences in the chemical coding of the nerve fibres may depend on their penile target-structure.

Tolerance to isosorbide dinitrate in isolated strips of rabbit corpus cavernosum

The aim of this study was to investigate whether prolonged exposure to a high concentration of isosorbide dinitrate (ISDN) would result in tolerance being developed against its relaxant activity in strips of corpus cavernosum, pre-contracted by phenylephrine. Under these conditions, relaxation induced by ISDN was found to be significantly reduced. Strips made tolerant to ISDN remained fully responsive to sodium nitroprusside and papaverine. Electrical field stimulation evoked relaxations which were persistent in the presence of tolerance-inducing conditions. These results indicate that desensitization of guanylate cyclase activity is not likely to be the operating mechanism for nitrate tolerance. We suggest that tolerance may result from the impairment of biotransformation of ISDN in rabbit cavernosal smooth muscle.

An in vitro study of nonadrenergic-noncholinergic activity on the cavernous tissue of mouse

The relaxant effects of electrical field stimulation (EFS) and exogenously applied acetylcholine (ACh) or acidified NaNO2 (a-NaNO2) were investigated in the isolated mouse corpus cavernosum precontracted with phenylephrine hydrochloride (PE). Tetrodotoxin (TTX) blocked the relaxant effects of EFS completely, whereas it had no effect on the responses to ACh or a-NaNO2. Guanethidine and indomethacin failed to affect the electrically or ACh-induced relaxations. Atropine completely blocked the effect of ACh; however, it caused a slight reduction in the relaxation evoked by EFS. NG-Nitro-L-arginine (L-NOARG) reduced the effects of EFS and ACh significantly, but it was ineffective on the relaxations induced by a-NaNO2. The inhibitory action of L-NOARG was partly restored by L-arginine, but not by D-arginine. Methylene blue (MB) and hydroxocobalamin (HC) exhibited significant inhibition on the relaxations evoked by EFS, ACh and a-NaNO2. Hydroquinone (HQ) reduced relaxation due to a-NaNO2, but did not affect that of EFS and ACh. Our findings suggest that EFS-induced relaxations of mouse cavernosal tissue are mediated by a transmitter which probably resembles an organic nitrate.

Sexual behavior in male rats after nitric oxide synthesis inhibition

The influence of the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) on the copulatory behavior of sexually experienced male Wistar rats was investigated. L-NAME was injected i.p. 10 min before the onset of a session using a dose of 30 mg/kg (L-NAME 30 group), or 60 mg/kg (L-NAME 60 group). The copulatory sessions were terminated after the third ejaculation in the control group or after 1500 s in the L-NAME 30 and L-NAME 60 groups. L-NAME administration reduced the number of rats that achieved ejaculation by 43% and 86% in the L-NAME 30 and 60 groups, respectively. In both experimental groups only a few intromissions and an increased number of mountings were observed. An increase in the number of ultrasonic vocalizations in the 50 kHz band, a dose-dependent effect, was observed. The level of sexual motivation evaluated by mount latency was not influenced by inhibition of NO synthesis.

Comparison of the pharmacological response of human corpus cavernosal tissue with the response of rabbit cavernosal tissue

1. This study directly compares the response of cavernosal tissue obtained from sexually mature rabbits with the response of human corpus cavernosal tissue obtained during implant surgery for psychogenic impotence (five individual samples) to field stimulation and specific autonomic agonists. 2. At 2 g basal tension, field stimulation of the rabbit corpus cavernosal tissue produced a frequency dependent biphasic response consisting of an initial relaxation followed by contraction. Low frequency stimulation induced primarily relaxations whereas high frequency stimulation induced primarily contractions. FS of human corpus cavernosal tissue induced a frequency dependent contraction. 3. In general, the rabbit corpus cavernosal strips showed a significantly greater degree of spontaneous activity than the strips of human cavernosal tissue. 4. Phenylephrine stimulated a rapid and sustained increase in basal tension in both tissues. Although the isolated strips weighed the same, the magnitude of the response of the rabbit tissue was significantly greater than the response of the human tissue. 5. For both tissues, FS relaxations were completely inhibited by L-NAME showing that the relaxations were mediated by nitric oxide. Similarly, for both tissues, nitroprusside, ATP, and bethanechol induced similar dose-response relaxations of pre-stimulated tissue. 6. In conclusion, the major difference between the response of human and rabbit tissue to various forms of stimulation was that isolated strips of human corporal tissue responded to FS with contractions at all frequencies whereas the rabbit tissue responded to the relaxations at low frequencies of stimulation; a clear bi-phasic response at intermediate frequencies; and contraction at high frequencies.

Coexistence of nitric oxide synthase, tyrosine hydroxylase and vasoactive intestinal polypeptide in human penile tissue--a triple histochemical and immunohistochemical study

Recently, nitric oxide (NO) has been believed to act as a neuronal messenger to mediate penile erection. In the present study using human penile tissue, we investigated the coexistence of neuronal NO synthase (NOS), tyrosine hydroxylase (TH) and vasoactive intestinal polypeptide (VIP) by a triple staining method using NADPH diaphorase (ND) staining, a specific histochemical marker of neuronal NOS, and immunohistochemical staining for TH and VIP. Numerous ND-positive nerve fibers and TH-containing fibers were seen in axon bundles, but their distributions were different. Only a few axons in the bundles showed VIP immunoreactivity. Abundant fine varicose nerve terminals innervating cavernous smooth muscles and deep and helicine arteries were observed. The proportion of fibers showing TH-immunoreactivity in ND-positive terminals in the cavernous space was about 25%, and that of VIP was about 40%. Vasoactive intestinal polypeptide may act as a coworker in these fibers both in cavernous trabeculae and around arteries, as about 40% of NOS-containing fibers also showed VIP immunoreactivity. The physiological significance of the colocalization of TH and NOS is unclear, and further studies are required to know the physiological significance of the colocalization of NOS and other neurotransmitters in penile tissue.

Penile erection in the primate: induction with nitric-oxide donors

The primate model has been used for investigations on the physiology and pharmacology of erection. Recent in vitro investigations indicate that nitric oxide acts as the mediator of penile erection, but in vivo primate studies are needed to corroborate these findings. Penile erections were induced in a primate model using intracavernosal injections of nitric oxide donors s-nitrocysteine (NO-CYS) and sodium nitroprusside (SNP), and acetylcholine (ACh) which stimulates the formation of nitric oxide. Penile length and intracavernosal pressures following agonist injection were compared with baseline (flaccid) and control erections (elicited by injection of a papaverine/phentolamine/PGE1 standard mixture). Dose-response curves for each drug were determined with respect to maximal intracavernosal pressure, duration of effect and penile length, and systemic arterial pressure was monitored. All three agents induced erections, with dose-dependent increases in cavernosal pressure and penile length. The maximal cavernosal pressure attained was similar for all three agents, but the duration of action was significantly shorter with ACh (p < .05). Injection of L-nitro-arginine-methyl-ester (L-NAME), a nitric oxide synthase inhibitor, before injection of the nitric oxide donor shortened the duration of effect but did not alter maximal cavernosal pressure or penile length attained. Although systemic hypotension was induced by each agent, digital compression at the base of the penis at the time of injection prevented such changes. These results suggest that the primate is a useful model to evaluate the action of substances that induce or inhibit penile erection. The findings provide support for the hypothesis that nitric oxide is a mediator of penile erection and that nitric oxide donors may be useful in the treatment of erectile dysfunction.

Nitric oxide mediates penile erection in cats

The present study was undertaken to investigate the in vivo effects of nitric oxide (NO) mediating agents injected intracavernosally on penile erection in cats. All NO donors increased the cavernosal pressure and penile length in a dose-dependent manner. The maximal effects on cavernosal pressure and penile length induced by s-nitrosocysteine (NO-CYS) and s-nitroso-n-acetylpenicillamine (SNAP), respectively, were 8-fold and 5-fold increases in pressure, and 45% and 34% increases in length when compared with baseline values. These changes were comparable to that caused by the control drug combination (papaverine, phentolamine and prostaglandin E1). The effects of acetylcholine (ACh) and substance P on cavernosal pressure and penile length were less than those obtained with the control drug combination, NO-CYS (p < 0.01), or SNAP (p < 0.05). N omega-nitro-l-arginine-methyl-ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, significantly decreased the effects of NO-CYS, ACh and substance P on penile erection. This in vivo study with NO donors and an NOS inhibitor suggests that NO is a mediator of penile erection in cats.