A possible role for calcitonin-gene-related peptide in the regulation of the smooth muscle tone of the bladder and penis

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Role of the nitric oxide pathway and the endocannabinoid system in neurogenic relaxation of corpus cavernosum from biliary cirrhotic rats

BACKGROUND AND PURPOSE

Relaxation of corpus cavernosum, which is mediated by nitric oxide (NO) released from non-adrenergic non-cholinergic (NANC) neurotransmission, is critical for inducing penile erection and can be affected by many pathophysiological conditions. However, the peripheral effect of liver cirrhosis on erectile function is as yet unknown. The aim of the present study was to investigate the effect of biliary cirrhosis on NANC-mediated relaxation of rat corpus cavernosum and the possible roles of endocannabinoid and nitric oxide systems in this model.

EXPERIMENTAL APPROACH

Cirrhosis was induced by bile duct ligation. Controls underwent sham operation. Four weeks later, strips of corpus cavernosum were mounted in a standard organ bath and NANC-mediated relaxations were obtained by applying electrical field stimulation.

KEY RESULTS

The NANC-mediated relaxation was enhanced in corporal strips from cirrhotic animals. Anandamide potentiated the relaxations in both groups. Either AM251 (CB(1) antagonist) or capsazepine (vanilloid VR(1) antagonist), but not AM630 (CB(2) antagonist), prevented the enhanced relaxations of cirrhotic strips. Either the non-selective NOS inhibitor L-NAME or the selective neuronal NOS inhibitor L-NPA inhibited relaxations in both groups, but cirrhotic groups were more resistant to the inhibitory effects of these agents. Relaxations to sodium nitroprusside (NO donor) were similar in tissues from the two groups.

CONCLUSIONS AND IMPLICATIONS

Cirrhosis potentiates the neurogenic relaxation of rat corpus cavernosum probably via the NO pathway and involving cannabinoid CB(1) and vanilloid VR(1) receptors.

Direct inhibitory effect of adrenomedullin, calcitonin gene-related peptide, calcitonin, and amylin on cholecystokinin-induced contraction of guinea-pig isolated caecal circular smooth muscle cells

We recently reported the direct inhibitory effect of adrenomedullin on caecal circular smooth muscle cells via cAMP system. This study was designed to determine whether the structurally related peptides to adrenomedullin (i.e.; calcitonin gene-related peptide (CGRP), calcitonin, and amylin) can inhibit the cholecystokinin octapeptide (CCK-8)-induced contractile response by exerting a direct action on guinea-pig caecal circular smooth muscle cells, and to compare the inhibitory potency of these peptides. In addition, to elucidate each intracellular mechanisms, the effects of an inhibitor of cAMP-dependent protein kinase, inhibitors of particulate or soluble guanylate cyclase on the each peptide-induced relaxation were investigated. Adrenomedullin, CGRP, calcitonin, and amylin inhibited the contractile response produced by CCK-8 in a dose-dependent manner, with IC50 values of 0.14 nM, 0.37 nM, 5.4 nM, and 160 nM, respectively. An inhibitor of cAMP-dependent protein kinase significantly inhibited the relaxation produced by all of these peptides. On the contrary, inhibitors of particulate or soluble guanylate cyclase did not have any significant effect on the relaxation produced by these peptides. In this study, we demonstrated the direct inhibitory effects of the structurally related peptides to adrenomedullin (i.e.; CGRP, calcitonin, and amylin) on the isolated caecal circular smooth muscle cells via cAMP system. The order of potency was as follows; adrenomedullin falling dots CGRP > calcitonin > amylin.

Alpha-adrenoceptor-mediated penile erection in dogs: in vivo and in vitro observations

We have evaluated the role of adrenergic components in the pelvic splanchnic nerve on the erectile function in the dog. Electrical stimulation of pelvic splanchnic nerves increased blood flow in the internal pudendal artery and also elevated the cavernous pressure. These increases were blocked in part by phentolamine or methylene blue, but not by propranolol or atropine. The effects of cholinergic and adrenergic agonists and antagonists on mechanical responses were also examined in muscle strips obtained from various arteries in the intrapelvic region including the internal pudendal artery. Norepinephrine induced contraction in the iliac artery and relaxation in the internal pudendal artery, and both the contraction and relaxation responses were blocked by phentolamine but not by propranolol. These findings suggest that in the dog, alpha-adrenergic components projected through the pelvic splanchnic nerve may contribute to penile erection, together with cyclic GMP-mediated mechanisms.

Non-surgical management of erectile dysfunction

Erectile dysfunction is a common and distressing medical condition that is now highly amenable to treatment almost irrespective of the cause. Safe, non-surgical treatments with unequivocal efficacy are psychological therapy, intracorporeal injection of vasoactive drugs, transurethral vasodilators and oral sildenafil, all of which have been reported to have a 50-70% overall response rate. Vacuum constriction devices are acceptable for some, usually older patients and oral yohimbine is thought to have marginal efficacy. Local creams to induce or enhance erectile function are currently being investigated. There is no place for androgen supplementation unless the patient is profoundly hypogonadal. Treatment of hyperprolactinaemia is very effective but is a rare cause of erectile dysfunction. As intercourse may entail an unfamiliar level of physical activity, it is sensible to ensure that the patient is able to climb a flight or two of stairs comfortably without provoking undue breathlessness or chest pain and to provide suitable advice about technique before commencing treatment. Once it is clear to the patients that erectile dysfunction can be satisfactorily overcome, the long-term use of treatments to do so tends to wane. Thus, although the prospect of effective treatment for what had been for many a distressing life sentence has the potential to place new demands on the health service, there is no evidence that restrictions on prescribing will prove economically rational.

Intracavernosal forskolin: role in management of vasculogenic impotence resistant to standard 3-agent pharmacotherapy

PURPOSE

We investigated forskolin, a direct adenylate cyclase activator, as an intracavernosal vasoactive agent in management of vasculogenic impotence.

MATERIALS AND METHODS

Concentration responses for forskolin and prostaglandin E1 induced relaxation of phenylephrine precontracted strips of human corpus cavernosum smooth muscle were constructed in vitro. Cyclic adenosine monophosphate (cAMP) synthesis was determined with papaverine, phentolamine, prostaglandin E1 and forskolin in human corpus cavernosum smooth muscle cell cultures. Dose-dependent hemodynamic responses to intracavernosal forskolin (5 to 20 micrograms) were evaluated in a New Zealand White rabbit model. Safety and efficacy outcome data were obtained in vasculogenically impotent patients who signed informed consent and met strict inclusion and exclusion criteria that included having had standard self-injection therapies fail.

RESULTS

In vitro forskolin and prostaglandin E1 alone caused concentration dependent relaxation with an EC50 of approximately 200 nm. and 16 nm., respectively. When the 2 agents were combined, the concentration response curve for relaxation shifted to the left. cAMP production was highest in cells treated with prostaglandin E1 and forskolin and was unaffected by papaverine or phentolamine. In 3 animals, equilibrium intracavernosal pressure and duration of erection had a dose dependent increase. Clinical investigation in 31 patients showed no adverse events with a mean of 14 +/- 4, range 11 to 18 months of followup. Overall 61% reported improvement in rigidity and/or erection duration using intracavernosal forskolin (98 micrograms./ml.), papaverine (29 mg./ml.), phentolamine (0.98 mg./ml.) and prostaglandin E1 (9.8 micrograms./ml.).

CONCLUSIONS

Forskolin is a United States Food and Drug Administration nonapproved vasoactive agent that acts in synergism with prostaglandin E1 to induce smooth muscle relaxation. In combination with other vasoactive agents, forskolin has demonstrated preliminary safety and efficacy in patients with vasculogenic impotence resistant to standard 3-agent pharmacotherapy.

Intracavernous pharmacotherapy: treatment for the aging erectile response

Fueled by serendipity, observation, and direct scientific investigations over the last 15 years the normal mechanisms of erection, and the pathophysiology of erectile dysfunction have been revealed. The demonstrations that vasoactive injections could produce penile erection without benefit of psychic or tactile stimuli revolutionized the diagnosis and treatment of erectile dysfunction by providing a direct test of end organ integrity or deficiency. This article reviews the clinical pharmacology of vasoactive corporal agents and outlines what has been surmised about the aging erectile response.

Adenosine modulation of neurotransmission in penile erection

1. Adenosine inhibited the noradrenaline-induced contraction of rabbit corpus cavernosum in a dose-dependent manner. The effect of adenosine was greater in intact corpus cavernosa than in endothelium-denuded preparations. This finding indicates that the relaxing effect of adenosine is partially endothelium-dependent and involved in the release of endothelium-derived relaxing factors. 2. Adenosine and its analogues relaxed the noradrenaline-induced contractile response as well as inhibited the transmural nerve induced contraction with the potency order: NECA > R-PIA > adenosine. These data indicate that adenosine can modulate both the non-adrenergic non-cholinergic and adrenergic neurotransmission. DMPX, an adenosine antagonist selective for the A2 receptors, abolished the electrically elicited relaxation. However, CGS 21680, selective for A2a receptor, had no effect on relaxation. Therefore, adenosine receptors involved in the modulation of neurotransmission in rabbit corpus cavernosum appear to be A2b subtype. 3. Adenosine also induced an increase in human cavernosal arterial velocity and resistive index measured by colour duplex sonography. The combination of adenosine and 10 micrograms prostaglandin E1 was more effective in resistive index and erection grade than 20 micrograms prostaglandin E1 alone. Our results suggest that adenosine seems to be an important neuromodulator for penile erection and can be an effective and alternative combination in the treatment of impotence.

Intracellular mechanism of penile erection in monkeys

To elucidate the sequence of events between the release of neurotransmitters and cavernous smooth muscle relaxation in erection, we studied the role of the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) systems. In a well-established simian model, the effects of specific agonists and antagonists of the intracellular sequence for smooth muscle relaxation and potassium channel openers on the intracavernous pressure were examined. Sodium nitroprusside (10(-3) M), a nitric oxide releaser and thus a stimulant of the cGMP system, caused an increase in the intracavernous pressure from 82 to 115 cm H2O for 7 to 19 min and penile diameter from 24.8 +/- 2.28 to 43 +/- 4.87 mm. When nitroprusside was injected after methylene blue (10(-3) M), a specific antagonist of the enzyme guanylate cyclase, intracavernous pressure rise decreased significantly, but cromakalin, a potassium channel opener, provoked excellent increases after the block. A smaller dose of sodium nitroprusside (10(-4) M) caused an increase in intracavernous pressure from 35 to 85 cm H2O for 7 to 11.5 min. When nitroprusside was injected after zaprinast, a phosphodiesterase inhibitor, the increase in pressure ranged from 80 to 116 cm H2O for 15 to 30 min. Prostaglandin E1, an activator of the cAMP system, caused an increase in the intracavernous pressure of 20-80 cm H2O for 5 to 10 min, and an increase in penile diameter from 25 +/- 2.22 to 35 +/- 3.48 mm. The erectile response to PGE1, but not to cromakalin, was nearly abolished by ethylmaleimide, an adenylate cyclase blocker. The response to nitroprusside was significantly greater (P < 0.05) than to PGE1. Both systems, cAMP and cGMP, may be involved in cavernous smooth muscle relaxation, and cGMP is probably the predominant intracellular second messenger in penile erection in monkeys. Stimulants of the cGMP system, such as nitric oxide releasers, could represent a more physiological and effective approach in the treatment of erectile dysfunction.

Pathophysiology of erectile dysfunction

During the past decade, our knowledge of the hemodynamics, functional anatomy, neurophysiology, and neuropharmacology of erectile function has evolved substantially. The change of smooth muscle tone has emerged as a key factor in erection and detumescence. However, future studies are needed to elucidate the cellular and molecular basis of erectile physiology. With insight into normal physiology we will understand the pathologic process and be able to treat it.

Prostaglandin E1 and the nitric oxide donor linsidomine for erectile failure: a diagnostic comparative study of 40 patients

A total of 40 patients (average age 55.9 years, range 23 to 78 years) with erectile failure was enrolled in a study to compare 1 mg. of the nitric oxide donor linsidomine to 20 micrograms prostaglandin E1 administered for diagnostic purposes. Prostaglandin E1 was considered comparable to linsidomine by 10% of the patients, slightly superior by 15%, moderately superior by 20% and much superior by 55%. No patient rated linsidomine superior to prostaglandin E1. Objective evaluation of erectile response to linsidomine versus prostaglandin E1 by the investigator revealed no response in 7.5% versus 0% of the cases, tumescence in 57.5% versus 17.5%, semirigid erection in 22.5% versus 17.5% and full erection in 12.5% versus 65%, respectively. Duplex sonography after linsidomine and prostaglandin E1 with evaluation of peak flow velocities (centimeters per second) showed that the increase in peak flow velocity after linsidomine was at least a third less than the increase after prostaglandin E1. The appearance after linsidomine often resembled arterial insufficiency, whereas after prostaglandin E1 there was no evidence of arterial insufficiency. The erectile and hemodynamic response to the nitric oxide donor linsidomine was modest compared to that of prostaglandin E1. Therefore, linsidomine is not a genuine alternative to prostaglandin E1 for the diagnosis and treatment of male impotence.

Followup results of a combination of calcitonin gene-related peptide and prostaglandin E1 in the treatment of erectile dysfunction

Recent human and animal studies have shown a possible role for calcitonin gene-related peptide in penile erection and a therapeutic benefit in combination with prostaglandin E1 for autoinjection therapy. The ethical committee approved calcitonin gene-related peptide-prostaglandin E1 combination for cases of nonresponse or cavernous fibrosis to papaverine-phentolamine. Since June 1990, 65 patients (59 nonresponders and 6 with fibrosis) were injected with 5 micrograms. calcitonin gene-related peptide plus 10 micrograms. prostaglandin E1. Of the 59 nonresponders to papaverine-phentolamine 31 and of the 6 patients with fibrosis 5 had full erectile response. Of these 36 patients 2 experienced pain during the pharmacologically induced erection. A total of 39 patients who had had at least 20 autoinjections of calcitonin gene-related peptide plus prostaglandin E1 was available for minimum followup. There were no side effects, such as pain (the 2 patients with pain mentioned previously were not included in the autoinjection therapy group), systemic side effects or (increased) fibrosis. Our results show that a combination of calcitonin gene-related peptide and prostaglandin E1 may be beneficial to the treatment of impotence in carefully selected patients.

The role of cyclic adenosine monophosphate, cyclic guanosine monophosphate, endothelium and nonadrenergic, noncholinergic neurotransmission in canine penile erection

To elucidate the neuropharmacology of erection, we undertook an in vivo canine study to examine the role of cholinergic and nonadrenergic, noncholinergic (NANC) neuroeffectors and the sinusoidal endothelium in erection induced by electrostimulation. We also examined the effect of adenylate cyclase and guanylate cyclase blockers by intravenous injection of N-ethylmaleimide and methylene blue, respectively. In addition, the effects of intracavernous injection of the nitric oxide-releasing substance, nitroprusside, and bromocyclic adenosine monophosphate (AMP) and bromocyclic guanosine monophosphate (GMP) were also studied. In contrast to in vitro results, atropine reduced the increase of intracavernous pressure after neurostimulation (p = 0.029). Intracavernous injection of CHAPS to destroy the sinusoidal endothelium abolished the response to acetylcholine (p = 0.001), but only partially inhibited the response to electrostimulation (mean = 75% pressure increase, p = 0.022), indicating that neuronal nitric oxide plays a major role in penile erection. Methylene blue, a guanylate cyclase inhibitor, significantly inhibited the erectile response to both neurostimulation and sodium nitroprusside (p = 0.000 and 0.017, respectively). However, N-ethylmaleimide, an adenylate cyclase inhibitor, could not reduce the response to neurostimulation (p = 0.078). The erectile response to intracavernous injection of cGMP was significantly better than that induced by cAMP (p = 0.025). Our results suggest that both the cholinergic and NANC neuroeffectors and the sinusoidal endothelium are involved in erection. In addition, our data imply that the neuronal nitric oxide/cyclic GMP system is the most likely pathway for penile smooth muscle relaxation and erection.

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

We investigated the relaxant effect of electric field stimulation (EFS) on rabbit cavernous smooth muscle strips in vitro precontracted by phenylephrine. Effects of EFS were monitored alone, and following muscarinic receptor blockade, and inhibition of nitric oxide (NO) formation by L-N-monomethylarginine (L-NMMA) or by L-N-nitroarginine (L-NOARG). Atropine only slightly reduced the relaxant effect of EFS to 89.0 +/- 6.1 percent. Additional application of L-NMMA further reduced the relaxant effect to 37.3 +/- 15.3 percent. Substitution of L-NOARG for L-NMMA led to a more pronounced inhibition of relaxant effects to 16.2 +/- 8.7 percent. The results indicate that neurogenically induced relaxation of rabbit cavernous smooth muscle is mediated mainly by NO formation and argue against a substantial role of relaxing peptidergic neurotransmitters, such as vasoactive intestinal polypeptide and calcitonin-gene-related peptide, in penile erection.

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.

Nitric oxide mediates relaxation in rabbit and human corpus cavernosum smooth muscle

We investigated in vitro the relaxant effect of exogenous acetylcholine (ACh) and electric-field stimulation (EFS) on rabbit and human corpus cavernosum smooth muscle strips (CC) precontracted with phenylephrine. The effects of EFS and ACh were monitored alone, after muscarinic receptor blockade and after inhibition of nitric oxide (NO) formation with L-N-nitro-arginine (L-NOARG). In rabbit and human CC, both atropine and L-NOARG abolished the relaxant effects of ACh. The relaxant effects of EFS, however, were only slightly reduced by atropine to 97.5 +/- 17.5% in human CC and to 89.0 +/- 6.1% in rabbit CC. L-NOARG further reduced the EFS effects to 0.8 +/- 1.7% in human CC and to 16.2 +/- 8.7% in rabbit CC. In strips obtained from impotent patients with diabetes mellitus, the relaxant effects appeared to be significantly less than in strips from nondiabetic impotent men. Tetrodotoxin blocked the relaxant EFS effects in human and rabbit strips completely. The data indicate the important role of NO in cholinergically induced relaxation of cavernous smooth muscle in rabbits and humans. Our findings support the idea of NO as the nonadrenergic noncholinergic neurotransmitter in penile erection in both species. Rabbit erectile tissue might serve as an in vitro animal model for further investigation.

Calcitonin-gene-related peptide: a possible role in human penile erection and its therapeutic application in impotent patients

A functional study was done to examine a possible role of calcitonin-gene-related peptide in human penile erection and its possible therapeutic applications for patients with erectile dysfunction. In the determination of an effective dosage, 5 ng. (2 patients), 50 ng. (2 patients), 500 ng. (4 patients), 5 micrograms (4 patients) and 25 micrograms (7 patients) were injected intracavernously, and pulse and blood pressure were monitored. Arterial inflow was measured by Doppler sonography, smooth muscle relaxation was determined by the analysis of cavernous electrical activity and cavernous outflow occlusion was recorded by cavernosometry. In 12 patients the erectile response of prostaglandin E1 was compared to the response of an equal (6 patients) or decreased dose of prostaglandin E1 combined with an equal weight of calcitonin-gene-related peptide. In 14 patients the erectile response to the combination of calcitonin-gene-related peptide and prostaglandin E1 was compared to the response of prostaglandin E1 alone, and with a combination of 15 mg./ml. papaverine and 0.5 mg./ml. phentolamine. Calcitonin-gene-related peptide induced an increase in the penile arterial inflow, cavernous smooth muscle relaxation and cavernous outflow occlusion. Histochemical results indicated nerve fibers positive for calcitonin-gene-related peptide within the cavernous bodies. A dose-dependent erectile response to calcitonin-gene-related peptide was observed at doses of 500 ng. to 25 micrograms. Systemic side effects were first observed at a dose of 25 micrograms in 2 of 7 patients. The combination of calcitonin-gene-related peptide and prostaglandin E1 was more effective in inducing a full erection than either prostaglandin E1 alone or the combination of papaverine and phentolamine. Pain was reported in 4% of the patients who received the combination of calcitonin-gene-related peptide and prostaglandin E1, whereas 42% of those who received prostaglandin E1 alone reported pain. Our results suggest that calcitonin-gene-related peptide may be a possible neurotransmitter for penile erection. A combination of calcitonin-gene-related peptide and prostaglandin E1 seems to be an effective alternative combination in the treatment of impotence.

Difference in the actions of calcitonin gene-related peptide on pig detrusor and vesical arterial smooth muscle

Calcitonin gene-related peptide has been demonstrated in urinary bladder nerves, and suggested to play a role in local control of bladder motility. In isolated strips of pig detrusor muscle, calcitonin gene-related peptide did not affect spontaneous contractile activity, or contractions induced by high K+, carbachol, substance P, and electrical field stimulation. In contrast, calcitonin gene-related peptide elicited a concentration-dependent and pronounced (78-99%) relaxation of vesical arteries precontracted with endothelin-1, noradrenaline or prostaglandin F2 alpha. As a vasodilator, CGRP was approximately 50 times more potent than acetylcholine. Removal of the endothelium abolished acetylcholine-induced relaxation, but did not affect the relaxation produced by calcitonin gene-related peptide. Pretreatment with methylene blue, glibenclamide or indomethacin had no influence on CGRP's ability to relax the vessels. The inhibitor of NO-synthesis, NG-nitro-L-arginine, had no effect on the maximum vascular relaxation induced by calcitonin gene-relate peptide. It is concluded that in the pig, calcitonin gene-related peptide has no functionally important mechanical effects on isolated detrusor muscle strips, but is a potent dilator of vesical arteries. The vascular effects of the peptide are endothelium-independent, and seem to be exerted directly on the vascular smooth muscle.