Induced Penile Erection Research Articles

Effects of the serotonin receptor ligand methiothepin on reproductive behavior of the freshwater snail Biomphalaria glabrata: reduction of egg laying and induction of penile erection.

The biogenic monoamine serotonin (5-HT) has been reported to enhance egg laying in the freshwater gastropod Biomphalaria glabrata, an intermediate host for human blood flukes. Methiothepin, a vertebrate 5-HT(1/2) receptor ligand which binds with high affinity to a 5-HT receptor (5-HTlym) in Lymnaea stagnalis was tested for its ability to block egg laying in B. glabrata as a possible target for snail control. A single 30-min application of methiothepin (1 microM) was sufficient to prevent egg laying for over 1 week and did so in a dose-dependent fashion. Furthermore, single applications of methiothepin (1 microM and 10 microM) induced penile erection in a high percentage of snails tested. Latency to erection was long (at least 8 hr), but the duration of erection was long-lasting (up to 48 hr). Despite the erections, methiothepin-treated snails failed to achieve copulations. The pharmacological effect of methiothepin on both male and female reproductive processes is similar to that produced in other molluscs, and points to the gene for the 5-HT receptor mediating or modulating both or either processes as a potential target of snail control strategies. J. Exp. Zool. 289:202-207, 2001.

EP 60761 and EP 50885, two hexarelin analogues, induce penile erection in rats

The effect of hexarelin and four related peptide analogues, EP 40904, EP 40737, EP 50885 and EP 60761, injected into the paraventricular nucleus of the hypothalamus of male rats in doses between 2 and 2000 ng on spontaneous penile erection was studied. Of these peptides, EP 60761 and EP 50885, but not hexarelin, EP 40904 or EP 40737, increased dose-dependently the number of spontaneous penile erections. EP 60761 was active already at the dose of 20 ng, which induced the sexual response in 70% of the treated rats. The maximal response was induced by 200 ng of the peptide. EP 50885 was less potent than EP 60761, with 1000 ng being the minimal effective dose and 2000 ng as the dose required to induce the maximal response. At the doses used, both peptides also increased slightly the number of spontaneous yawning episodes. EP 60761- and EP 50885-induced penile erection was prevented by the oxytocin receptor antagonist [d(CH 2) 5Tyr(Me) 2-Orn 8]vasotocin (0.1–1 μg) given intracerebroventricularly (i.c.v.), but not into the paraventricular nucleus (0.1–1μg), by the competitive nitric oxide (NO) inhibitor N G-nitro-L-arginine methyl ester ( l-NAME) given either into the paraventricular nucleus (10–20 μg) or i.c.v. (75–150 μg), by the N-type Ca 2+ channel blocker ω-conotoxin-GVIA (2–5 ng) or by the opiate morphine (1–10 μg), but not by the dopamine receptor antagonist ( Z)-4-[3-[2-(trifluoromethyl)-9 H-thioxanthen-9-ylidene]propyl]-1-piperazine-ethanol ( cis-flupenthixol) (10 μg) or by the N-methyl- d-aspartic acid (NMDA) receptor antagonist (5 R,10 S)-(+)-5-methyl-10,11-dihydro-5 H-dibenzo[ a, d]cyclohepten-5,10-imine ((+)-MK-801) (1 μg), all given into the paraventricular nucleus before either peptide. The present results show that EP 60761 and EP 50885 induced penile erection by increasing central oxytocin transmission, possibly by activating NO synthase in the cell bodies of oxytocinergic neurons located in the paraventricular nucleus that control penile erection.

Intracavernosal pressure monitoring in mice: responses to electrical stimulation of the cavernous nerve and to intracavernosal drug administration.

With the development of transgenic mice to evaluate mechanisms of erectile function, it appears particularly advantageous to develop a standardized mouse model of penile erection. The purpose of the study reported here was to evaluate the novel application of intracavernosal pressure (ICP) monitoring in the mouse during electrophysiologic and pharmacologic induction of penile erection. In anesthetized adult male mice, the cavernous nerves (CN) were isolated unilaterally, and the corpora cavernosa were exposed. A 24-gauge angiocath (intravenous catheter) was inserted into the right corpus cavernosum to monitor the ICP, and a 30.5-gauge needle was inserted into the left corpus cavernosum for intracavernosal drug administration. ICP was recorded during CN-stimulated or pharmacostimulated erections. Electrical stimulation of the CN significantly increased the ICP (from 10.09 +/- 2.01 to 34.62 +/- 2.71 mm Hg, P < .05), which then returned to baseline pressure after termination of the electrical stimulation. Pretreatment with intracavernosal administration of the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (0.1 mg), inhibited the electrical stimulation-induced changes in ICP (7.17 +/- 1.46 vs 10.38 +/- 2.17 mm Hg, not significant [NS]). Also, intracavernosal administration of papaverine (0.4 mg) produced a significant increase in ICP (from 8.51 +/- 0.69 to 26.37 +/- 5.7 mm Hg, P < .05). We concluded that this technique might be applied to perform quantitative erection physiologic experiments with the mouse as an economical and experimentally advantageous animal model, particularly with the development of transgenic mice to evaluate mechanisms of erectile function.

Feline penile erection induced by transurethral administration of sodium nitroprusside

Nitric oxide (NO) is an important mediator in the relaxation of cavernosal smooth muscle. The aim of this study was to investigate the in vivo feline erectile response after transurethral administration of sodium nitroprusside (SNP), a NO donor drug. Erectile responses after administration of transurethral SNP were compared with those elicited by an intracavernosal control triple-drug combination (1.65 mg papaverine, 25 microg phentolamine, and 0.5 microg prostaglandin E1). SNP was administered via a 20-gauge Jelco intravenous catheter in a volume of 200 microl and changes in intracavernosal pressure, penile length, and systemic blood pressure were monitored. The control triple-drug combination was administered via a 30-gauge needle at the end of each experiment to serve as a control reference. Transurethral administration of SNP (1-4 mg) induced penile erection in a dose-dependent manner with minimal changes in systemic blood pressure. The maximum increase in intracavernosal pressure and penile length after transurethral administration of SNP (4 mg) was significantly less than after the intracavernosal injection of the control triple-drug combination (P<0.01). These data suggest that transurethral administration of SNP can induce an erectile response in cats with minimal side effects.

Prospective Comparative Study with Intracavernous Sodium Nitroprusside and Prostaglandin E1 in Patients with Erectile Dysfunction

Purpose: To compare the effectiveness of intracavernous administration of sodium nitroprusside and prostaglandin E₁ to induce penile erection in men with erectile dysfunction. Material and Methods: 100 patients with erectile dysfunction entered the study prospectively. As part of the diagnostic workup, each patient received an intracavernous injection of 20 µg prostaglandin E₁ and a second injection of 600 µg sodium nitroprusside 1–7 days later. A tourniquet was placed at the base of the penis before each injection. The data recorded included time required to initiate tumescence, local and systemic side effects, objective and subjective quality of erections, duration of tumescence and patient satisfaction by means of a personal questionnaire. Results: Prostaglandin E₁ induced better overall responses than sodium nitroprusside, the difference being almost significant (p = 0.055). The overall duration of erections was also significantly longer with prostaglandin E₁ (mean 81.3 min) than with sodium nitroprusside (mean 65.4 min; p < 0.04). 67% of the patients considered the erections induced with prostaglandin E₁ to be of better quality than those with sodium nitroprusside, and only 11% stated that sodium nitroprusside was superior. Side effects were minimal with both drugs, the most frequent side effect being systemic hypotension, which was induced by sodium nitroprusside in 7% of the patients. Conclusions: The moderate risk of systemic hypotension and the lower potency of sodium nitroprusside to induce erections compared to prostaglandin E₁ rules out sodium nitroprusside as a routine alternative intracavernous drug in men with erectile dysfunction at the doses employed. Sodium nitroprusside, however, could be used in patients who have intolerance or penile pain with intracavernous prostaglandin E₁.

The influence of castration on pharmacologically induced penile erection in the cat.

The purpose of this study was to investigate the in vivo effects of intracavernosal injections of adrenomedullin (ADM), calcitonin gene-related peptide (CGRP), nociceptin, vasoactive intestinal polypeptide (VIP), sodium nitroprusside (SNP), and prostaglandin E1 (PGE1) on penile erection in castrated and intact (control) anesthetized cats. Erectile responses to ADM, CGRP, nociceptin, VIP, SNP, and PGE1 were compared with responses to a standard triple-drug combination (1.65 mg of papaverine, 25 microg of phentolamine, and 0.5 microg of PGE1) in both castrated and control cats. In control animals, ADM, CGRP, nociceptin, VIP, SNP, and PGE1 induced penile erections similar to those elicited by the triple-drug combination. However, in castrated animals, there was a significant decrease in erectile response; the response to intracavernosal injection of the standard triple-drug combination in castrated cats was 28% of that of the control group of animals. Serum testosterone levels demonstrated a significant (P < 0.0001) positive correlation (r = 0.52) with intracavernosal pressure in response to the standard combination. A marked reduction in serum testosterone levels was observed in castrated cats when measured by radioimmunoassay (0.34 +/- 0.1 ng/dl in castrated cats, compared with 31.15 +/- 6 ng/dl in control cats). These data suggest that the presence of testosterone is a necessary prerequisite to sustain a pharmacologically induced penile erection in the cat.

Comparison of Alprostadil (Caverject) and a combination of vasoactive drugs as local injections for the treatment of erectile dysfunction.

The efficiency and side effects of a single dose of 20 mcg of intracorporeally applied Alprostadil (Caverject, Upjohn), a prostaglandin E1, in inducing penile erection were examined in 30 patients. In addition, the effect of this dose of prostaglandin E1 was compared to that of 30 mg of papaverine plus 0.5 mg of regitine (phentolamine). All patients received a first injection of the combination of the vasoactive drugs and a second injection of the prescribed dose of Caverject. The degree of erection, time interval between injections and achievement of full erection as well as side effects during and after injection were compared. All patients had a burning sensation during the injection of Caverject. Two patients given the vasoactive combination got priapism and were evacuated; this complication was not reported for Caverject. In the doses used Caverject was superior to papaverine plus phentolamine in inducing penile erection and in achieving a higher grade of erection.

Role of radionuclide phallogram in therapeutic decision-making for erectile dysfunction

Objective. The purpose of this study is to evaluate the role of radionuclide phallograms in therapeutic decision-making for erectile dysfunction. Method. Forty-eight impotent men being considered for pharmacologically-induced penile erection therapy (PIPE) had radionuclide phallograms (RP) as part of their evaluation. RP were performed using 99mTc-labeled autologous red blood cells and provided a measurement of penile blood volume (PBV) change following the intracorporeal injection of 0.25 to 0.3 mL of a papaverine/phentolamine mixture. Results. Thirty-eight patients showed a good response with a mean PBV increase 2.6 times baseline (range 1.2 to 8.9). Ten patients had significantly lower PBV changes ( P = 0.001) than the first group, with a mean PBV increase of 1.6 times baseline (range 1.1 to 2.4). These ten patients were dissatisfied with pharmacologically induced penile erection (PIPE) therapy after an unsuccessful treatment trial. Conclusion. We conclude that the RP can help to discriminate between patients who will benefit from PIPE therapy and those who will not.

Evaluation of a no-needle penile injector: a preliminary study evaluating tissue penetration and its hemodynamic consequences in the rat

Objectives Intracavernous needle injection is an effective delivery method for pharmacotherapy of erectile dysfunction. Needle phobia, pain, and concern about local tissue injury have stimulated the search for new, less invasive means of inducing penile erection. In this preliminary communication, we evaluate a jet injector as an alternative to needle injection for intracavernous delivery of vasoactive drugs. Methods Jet injection was evaluated in three groups of rats receiving either India ink, saline, or papaverine into the penis. The ability of the jet injection to penetrate through the tunica albuginea and deliver liquid to the corpora cavernosa smooth muscle was assessed by the degree of staining within the corpus cavernosum (ink group), histologic change (saline group), and rise in intracavernous pressure (papaverine group). Erectile capacity following cavernous nerve electric stimulation was compared before and 1 hour after injection of saline or papaverine. Results Ink traversed the skin and tunica albuginea with extensive deposition noted within the cavernous spaces. Varying degrees of subcutaneous hemorrhage were seen with saline jet injection; however, the corpus cavernous smooth muscles showed no evidence of injury. Jet injection of papaverine 3250 gmg significantly increased cavernous pressure (39.4 ± 4.6 cm H 2O) compared with saline injection (2.8 ± 1.3 cm H 2O). Conclusions We conclude that acute jet injection is an effective method for intracavernous delivery of drugs. Long-term effects should be evaluated prior to clinical use.

Oxytocin increases nitric oxide production in the paraventricular nucleus of the hypothalamus of male rats: correlation with penile erection and yawning

A dose of oxytocin (50 ng i.c.v.) that induces penile erection and yawning, increased the concentration of NO2− from 0.98±0.29 to 4.2±0.79 μM and of NO3− from 5.6±0.33 to 12.03±0.99 μM in the dialysate from the paraventricular nucleus of the hypothalamus of male rats, as measured by in vivo microdialysis. NO2− concentration was also increased by [Thr4,Gly7]-oxytocin (100 ng i.c.v.) and oxytocin(1–8) (1 μg i.c.v.), which also induced penile erection and yawning, but not by oxytocin(1–6) (1 μg i.c.v.) or oxytocin(7–9) (1 μg i.c.v.), which were unable to induce these behavioral responses. The oxytocin effect on NO2− concentration, penile erection and yawning was prevented by the oxytocin receptor antagonist, d(CH2)5Tyr(Me)-Orn8-vasotocin (1 μg i.c.v.), or by the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (200 μg i.c.v.), but not by the dopamine receptor antagonist, haloperidol (0.5 mg/kg i.p.). The nitric oxide scavenger, hemoglobin (200 μg i.c.v.), prevented oxytocin-induced NO2− concentration increase, but was unable to prevent penile erection and yawning. Methylene blue (300 μg i.c.v.), an inhibitor of guanylate cyclase, was ineffective on oxytocin-induced NO2− concentration increase, but prevented the behavioral responses. The results suggest that oxytocin induces penile erection and yawning by increasing nitric oxide synthase activity in the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas and mediating the behavioral responses.

Neurotransmission and the contraction and relaxation of penile erectile tissues

The balance between contractant and relaxant factors controls the smooth muscle of the corpus cavernosum and determines the functional state of the penis (detumescence and flaccidity versus tumescence and erection). Noradrenaline contracts both the corpus cavernosum and penile vessels, mainly via stimulation of alpha(1)-adrenoceptors. Recent investigations have demonstrated the presence of several subtypes of alpha 1-adrenoceptors (alpha(1A), alpha(1B), and alpha(1D)) in the human corpus cavernosum and also that the noradrenaline-induced contraction in this tissue is probably mediated by two or, possibly, three receptor subtypes. Even if much of the available in vitro information suggests that endothelins (ETs) may be of importance for mechanisms of detumescence and flaccidity, the role of the peptides in the control of penile smooth-muscle tone in vivo is unclear, as is the question as to whether they can contribute to erectile dysfunction. For further evaluation of the clinical importance of ETs in penile physiology and pathophysiology, clinical studies on ET-receptor antagonists would be of interest. Neurogenic nitric oxide (NO) has been considered the most important factor for relaxation of penile vessels and the corpus cavernosum, but recent studies in mice lacking neurogenic NO synthase (NOS) have shown these animals to have normal erections. This focuses interest on the role of endothelial NOS and on other agents released from nerves or endothelium. For the time being the most effective means of inducing penile erection in men involves the intracavernous administration of prostaglandin E1 (PGE1). PGE1 may act partly by increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP). Recent results obtained with the adenylate cyclase stimulator forskolin suggest that penile smooth-muscle relaxation leading to penile erection can be achieved through the cAMP pathway. Thus, transmitters and agents acting through this second-messenger system may significantly contribute to relaxation of penile smooth muscle and to erection.

Prevention by Morphine of N-Methyl- d-Aspartic Acid-Induced Penile Erection and Yawning: Involvement of Nitric Oxide

The effect of morphine on the increase of NO 2 − and NO 3 − concentration in the dialysate obtained with a microdialysis probe implanted in the paraventricular nucleus of the hypothalamus, and penile erection and yawning induced by N -methyl- d-aspartic acid (NMDA) was studied in male rats. NMDA (50 ng) injected in the paraventricular nucleus of the hypothalamus, induced penile erection and yawning and increased NO 2 − from 1.10 ± 0.28 μM to 7.30 ± 1.10 μM and NO 3 − from 5.05 ± 0.71 μM to 11.03 ± 1.61 μM. Morphine (1–10 μg), but not U-69,593 (10 μg), a selective agonist of the κ opiate receptor subtype, prevented in a dose-dependent manner NMDA-induced increase in NO 2 − and NO 3 − concentration when injected in the paraventricular nucleus 15 min before NMDA. Morphine prevention of NMDA-induced NO 2 − and NO 3 − increase was related to a concomitant decrease in the number of penile erection and yawning episodes induced by the excitatory amino acid. Morphine effect was not observed in male rats treated with the opiate receptor antagonist naloxone (10 μg) microinjected in the paraventricular nucleus 15 min before morphine. The present results suggest that morphine prevents an NMDA-induced increase in paraventricular NO production, penile erection, and yawning by inhibiting NO synthase activity in the paraventricular nucleus of the hypothalamus through the stimulation of opioid receptors of the μ subtype.

Brain somatostatin depletion by cysteamine attenuates the penile erection induced by serotonergic and dopaminergic, but not by cholinergic, activation in rats

To clarify the role of brain somatostatin in the expression of penile erection, the effects of cysteamine, a somatostatin depletor, on the penile erection induced by serotonergic, cholinergic and dopaminergic stimulants were investigated in rats. Fenfluramine (0.1–10 mg/kg, i.p.), pilocarpine (0.032–3.2 mg/kg, i.p.) and apomorphine (0.01–1 mg/kg, i.p.) induced penile erection in rats, with bell-shaped dose-response curves. Pretreatment with cysteamine (200 mg/kg, s.c.) significantly attenuated the penile erection induced by fenfluramine and apomorphine, but scarcely affected that induced by pilocarpine. Neurochemical measures revealed that cysteamine pretreatment significantly reduced the somatostatin content in all brain regions examined. These results provide the first pharmacological evidence that the brain somatostatin may play an important role in drug-induced penile erection.

Brain somatostatin depletion by cysteamine attenuates the penile erection induced by serotonergic and dopaminergic, but not by cholinergic, activation in rats

To clarify the role of brain somatostatin in the expression of penile erection, the effects of cysteamine, a somatostatin depletor, on the penile erection induced by serotonergic, cholinergic and dopaminergic stimulants were investigated in rats. Fenfluramine (0.1–10 mg/kg, i.p.), pilocarpine (0.032–3.2 mg/kg, i.p.) and apomorphine (0.01–1 mg/kg, i.p.) induced penile erection in rats, with bell-shaped dose-response curves. Pretreatment with cysteamine (200 mg/kg, s.c.) significantly attenuated the penile erection induced by fenfluramine and apomorphine, but scarcely affected that induced by pilocarpine. Neurochemical measures revealed that cysteamine pretreatment significantly reduced the somatostatin content in all brain regions examined. These results provide the first pharmacological evidence that the brain somatostatin may play an important role in drug-induced penile erection.

Cardiovascular protection by ginsenosides and their nitric oxide releasing action.

1. In an animal model in vivo, ginsenosides (GS), saponins from Panax ginseng, were shown to protect against myocardial ischaemia/reperfusion damage with concomitant increased 6-keto-PGF1 alpha and decreased lipid peroxidation. 2. In perfused rabbit lung in situ and isolated rabbit aortic rings, GS protected the pulmonary and aortic endothelium against electrolysis-induced free radical injury. Purified components of GS, Rb1 and especially Rg1, relaxed pulmonary vessels and this effect was eliminated by nitro-L-arginine, an inhibitor of nitric oxide (NO) synthase. 3. In cultured bovine aortic endothelial cells, GS enhanced the conversion of [14C]-L-arginine to [14C]-L-citrulline, indicating an increased release of NO. 4. As the neurotransmitter inducing penile erection, NO release was shown to be enhanced by GS in rabbit corpus cavernosum (CC) in vitro. Ginsenosides enhanced both acetylcholine-induced and transmural nerve stimulation-activated relaxation associated with increased tissue cGMP. The latter effect was eliminated by tetrodotoxin and was associated with decreased tissue cGMP. Ginsenoside-enhanced CC relaxation was attenuated by nitro-L-arginine and oxyhaemoglobin, and enhanced by superoxide dismutase. 5. It is postulated that cardiovascular protection by GS may be partly mediated by the release of NO, a potent antioxidant, and that the GS-enhanced release of NO from endothelial cells, especially from perivascular nitric oxidergic nerves in the CC, may partly account for the aphrodisiac effect of Panax ginseng used in traditional Chinese medicine.

Nitric Oxide-Dependent Penile Erection in Mice Lacking Neuronal Nitric Oxide Synthase

Nitric oxide (NO) has been implicated as a mediator of penile erection, because the neuronal isoform of NO synthase (NOS) is localized to the penile innervation and NOS inhibitors selectively block erections. NO can also be formed by two other NOS isoforms derived from distinct genes, inducible NOS (iNOS) and endothelial NOS (eNOS). To clarify the source of NO in penile function, we have examined mice with targeted deletion of the nNOS gene (nNOS- mice). Mating behavior, electrophysiologically induced penile erection, isolated erectile tissue isometric tension, and eNOS localization by immunohistochemistry and Western blot were performed on nNOS- mice and wild-type controls. Both intact animal penile erections and isolated erectile tissue function are maintained in nNOS mice, in agreement with demonstrated normal sexual behaviors, but is stereospecifically blocked by the NOS inhibitor, L-nitroarginine methyl ester (L-NAME). eNOS is abundantly present in endothelium of penile vasculature and sinusoidal endothelium within the corpora cavemosa, with levels that are significantly higher in nNOS- mice than in wild-type controls. eNOS mediates NO-dependent penile erection in nNOS- animals and normal penile erection. These data clarify the role of nitric oxide in penile erection and may have implications for therapeutic agents with selective effects on NOS isoforms.

Nitric oxide donors induce penile erection and yawning when injected in the central nervous system of male rats

In order to provide further support for a role of central nitric oxide as a mediator of penile erection and yawning, the nitric oxide donors sodium nitroprusside, hydroxylamine, isoamyl nitrite and S-nitroso- N-acetyl-penicillamine were injected into the lateral ventricles (i.c.v) or into the paraventricular nucleus of the hypothalamus of male rats. Of the above compounds injected i.c.v., only isoamyl nitrite (10–100 μg) induced penile erection and yawning, while the others induced dramatic behavioral changes, such as motor hyperactivity and convulsions, that masked the above responses. Nevertheless, nitric oxide donors in doses ranging from 10 to 50 μg, for except S-nitroso- N-acetyl-penicillamine that was injected only at the dose of 10 μg and isoamyl nitrite that was not injected at all because of poor solubility, induced penile erection and yawning when injected in the paraventricular nucleus. Nitric oxide donor-induced responses were prevented by methylene blue and LY 83583, inhibitors of guanylate cyclase, the best known target of nitric oxide, given i.c.v. but not in the paraventricular nucieus. However, 8-bromo-guanosine 3′:5′-cyclic monophosphate (8-Br-cGMP), a stable cGMP analog, and hemoglobin, a nitric oxide scavenger, were ineffective in inducing and preventing, respectively, penile erection and yawning when injected either i.c.v. or in the paraventricular nucleus. Nitric oxide donor-induced responses were also prevented by the nonapeptide oxytocin receptor antagonist d(CH 2) 5-Tyr(Me)-Orn 8-vasotocin given i.c.v. but not in the paraventricular nucleus. The present results suggest that nitric oxide donors induce penile erection and yawning by activating central oxytocinergic transmission in the paraventricular nucleus of the hypothalamus via a cGMP-independent mechanism.

Intraoperative Electrostimulation of Cavernous Nerve: Technique, Results and Limitations

Purpose We studied the feasibility of inducing penile erection intraoperatively by stimulation of the cavernous nerves. Materials and Methods In 16 men undergoing retropubic radical prostatectomy and 6 undergoing penile surgery for venous leakage electrostimulation was applied to both sides of the prostatic apex (prostatectomy group) or the hilum of the penis (venous surgery group). Results Electrostimulation produced visible erection in 8 of the 16 prostatectomy patients and an increase in intracavernous pressure in 5 of the 6 venous surgery patients. Conclusions Electrostimulation of the cavernous nerves intraoperatively to produce penile erection is feasible. However, the technique must be further refined to be clinically useful, that is to localize the neurovascular bundle in men undergoing prostatectomy.

Suppression by Prolactin of the Electrically Induced Erectile Response through its Direct Effect on the Corpus Cavernosum Penis in the Dog

Purpose Men become impotent when exposed to hyperprolactinemia. To clarify its mechanisms the effects of intracorporal infusion of prolactin on electrically induced penile erection were evaluated in 12 male dogs. Materials and Methods Prolactin (10 microgram/ml.) or control saline was directly infused into the corpus cavernosum penis 5 minutes before electrical pulse stimulation of the pelvic nerve and the intracorporal pressure was monitored. Results In 8 dogs erection was markedly suppressed or completely abolished by prolactin. In the remaining 4, this effect of prolactin became manifest only when the ipsilateral internal pudenal artery was ligated. Saline infusion was without effect. Conclusions An excess of prolactin directly inhibited the smooth muscle relaxation of corpus cavernosum penis.

Suppression by prolactin of the electrically induced erectile response through its direct effect on the corpus cavernosum penis in the dog.

Men become impotent when exposed to hyperprolactinemia. To clarify its mechanisms the effects of intracorporal infusion of prolactin on electrically induced penile erection were evaluated in 12 male dogs. Prolactin (10 micrograms./ml.) or control saline was directly infused into the corpus cavernosum penis 5 minutes before electrical pulse stimulation of the pelvic nerve and the intracorporal pressure was monitored. In 8 dogs erection was markedly suppressed or completely abolished by prolactin. In the remaining 4, this effect of prolactin became manifest only when the ipsilateral internal pudenal artery was ligated. Saline infusion was without effect. An excess of prolactin directly inhibited the smooth muscle relaxation of corpus cavernosum penis.