Capsaicin-induced inhibition of motility of the rat isolated vas deferens: do multiple neuropeptides mediate the visceromotor effects of capsaicin?

Final report on the safety assessment of capsicum annuum extract, capsicum annuum fruit extract, capsicum annuum resin, capsicum annuum fruit powder, capsicum frutescens fruit, capsicum frutescens fruit extract, capsicum frutescens resin, and capsaicin

Capsicum-derived ingredients function as skin-conditioning agents--miscellaneous, external analgesics, flavoring agents, or fragrance components in cosmetics. These ingredients are used in 19 cosmetic products at concentrations as high as 5%. Cosmetic-grade material may be extracted using hexane, ethanol, or vegetable oil and contain the full range of phytocompounds that are found in the Capsicum annuum or Capsicum frutescens plant (aka red chiles), including Capsaicin. Aflatoxin and N-nitroso compounds (N-nitrosodimethylamine and N-nitrosopyrrolidine) have been detected as contaminants. The ultraviolet (UV) absorption spectrum for Capsicum Annuum Fruit Extract indicates a small peak at approximately 275 nm, and a gradual increase in absorbance, beginning at approximately 400 nm. Capsicum and paprika are generally recognized as safe by the U.S. Food and Drug Administration for use in food. Hexane, chloroform, and ethyl acetate extracts of Capsicum Frutescens Fruit at 200 mg/kg resulted in death of all mice. In a short-term inhalation toxicity study using rats, no difference was found between vehicle control and a 7% Capsicum Oleoresin solution. In a 4-week feeding study, red chilli (Capsicum annuum) in the diet at concentrations up to 10% was relatively nontoxic in groups of male mice. In an 8-week feeding study using rats, intestinal exfoliation, cytoplasmic fatty vacuolation and centrilobular necrosis of hepatocytes, and aggregation of lymphocytes in the portal areas were seen at 10% Capsicum Frutescens Fruit, but not 2%. Rats fed 0.5 g/kg day-1 crude Capsicum Fruit Extract for 60 days exhibited no significant gross pathology at necropsy, but slight hyperemia of the liver and reddening of the gastric mucosa were observed. Weanling rats fed basal diets supplemented with whole red pepper at concentrations up to 5.0% for up to 8 weeks had no pathology of the large intestines, livers, and kidneys, but destruction of the taste buds and keratinization and erosion of the gastrointestinal (GI) tract were noted in groups fed 0.5% to 5.0% red pepper. The results of 9-and 12-month extension of this study showed normal large intestines and kidneys. In rabbits fed Capsicum Annuum Powder at 5 mg/kg day-1 in the diet daily for 12 months damage to the liver and spleen was noted. A rabbit skin irritation test of Capsicum Annuum Fruit Extract at concentrations ranging from 0.1% to 1.0% produced no irritation, but Capsicum Frutescens Fruit Extract induced concentration-dependent (at 25 to 500 microg/ml) cytotoxicity in a human buccal mucosa fibroblast cell line. An ethanol extract of red chili was mutagenic in Salmonella typhimurium TA98, but not in TA100, or in Escherichia coli. Other genotoxicity assays gave a similar pattern of mixed results. Adenocarcinoma of the abdomen was observed in 7/20 mice fed 100 mg red chilies per day for 12 months; no tumors were seen in control animals. Neoplastic changes in the liver and intestinal tumors were observed in rats fed red chili powder at 80 mg/kg day-1 for 30 days, intestinal and colon tumors were seen in rats fed red chili powder and 1,2-dimethyl hydrazine, but no tumors were observed in controls. In another study in rats, however, red chile pepper in the diet at the same dose decreased the number of tumors seen with 1,2-dimethylhydrazine. Other feeding studies evaluated the effect of red chili peppers on the incidence of stomach tumors produced by N-methyl-N'-nitro-N-nitrosoguanidine, finding that red pepper had a promoting effect. Capsicum Frutescens Fruit Extract promoted the carcinogenic effect of methyl(acetoxymethyl)nitrosamine (carcinogen) or benzene hexachloride (hepatocarcinogen) in inbred male and female Balb/c mice dosed orally (tongue application). Clinical findings include symptoms of cough, sneezing, and runny nose in chili factory workers. Human respiratory responses to Capsicum Oleoresin spray include burning of the throat, wheezing, dry cough, shortness of breath, gagging, gasping, inability to breathe or speak, and, rarely, cyanosis, apnea, and respiratory arrest. A trade name mixture containing 1% to 5% Capsicum Frutescens Fruit Extract induced very slight erythema in 1 of 10 volunteers patch tested for 48 h. Capsicum Frutescens Fruit Extract at 0.025% in a repeated-insult patch test using 103 subjects resulted in no clinically meaningful irritation or allergic contact dermatitis. One epidemiological study indicated that chili pepper consumption may be a strong risk factor for gastric cancer in populations with high intakes of chili pepper; however, other studies did not find this association. Capsaicin functions as an external analgesic, a fragrance ingredient, and as a skin-conditioning agent--miscellaneous in cosmetic products, but is not in current use. Capsaicin is not generally recognized as safe and effective by the U.S. Food and Drug Administration for fever blister and cold sore treatment, but is considered to be safe and effective as an external analgesic counterirritant. Ingested Capsaicin is rapidly absorbed from the stomach and small intestine in animal studies. Subcutaneous injection of Capsaicin in rats resulted in a rise in the blood concentration, reaching a maximum at 5 h; the highest tissue concentrations were in the kidney and lowest in the liver. In vitro percutaneous absorption of Capsaicin has been demonstrated in human, rat, mouse, rabbit, and pig skin. Enhancement of the skin permeation of naproxen (nonsteroidal anti-inflammatory agent) in the presence of Capsaicin has also been demonstrated. Pharmacological and physiological studies demonstrated that Capsaicin, which contains a vanillyl moiety, produces its sensory effects by activating a Ca2 +-permeable ion channel on sensory neurons. Capsaicin is a known activator of vanilloid receptor 1. Capsaicin-induced stimulation of prostaglandin biosynthesis has been shown using bull seminal vesicles and rheumatoid arthritis synoviocytes. Capsaicin inhibits protein synthesis in Vero kidney cells and human neuroblastoma SHSY-5Y cells in vitro, and inhibits growth of E. coli, Pseudomonas solanacearum, and Bacillus subtilis bacterial cultures, but not Saccharomyces cerevisiae. Oral LD50 values as low as 161.2 mg/kg (rats) and 118.8 mg/kg (mice) have been reported for Capsaicin in acute oral toxicity studies, with hemorrhage of the gastric fundus observed in some of the animals that died. Intravenous, intraperitoneal, and subcutaneous LD50 values were lower. In subchronic oral toxicity studies using mice, Capsaicin produced statistically significant differences in the growth rate and liver/body weight increases. Capsaicin is an ocular irritant in mice, rats, and rabbits. Dose-related edema was observed in animals receiving Capsaicin injections into the hindpaw (rats) or application to the ear (mice). In guinea pigs, dinitrochlorobenzene contact dermatitis was enhanced in the presence of Capsaicin, injected subcutaneously, whereas dermal application inhibited sensitization in mice. Immune system effects have been observed in neonatal rats injected subcutaneously with Capsaicin. Capsaicin produced mixed results in S. typhimurium micronucleus and sister-chromatid exchange genotoxicity assays. Positive results for Capsaicin were reported in DNA damage assays. Carcinogenic, cocarcinogenic, anticarcinogenic, antitumorigenic, tumor promotion, and anti-tumor promotion effects of Capsaicin have been reported in animal studies. Except for a significant reduction in crown-rump length in day 18 rats injected subcutaneously with Capsaicin (50 mg/kg) on gestation days 14, 16, 18, or 20, no reproductive or developmental toxicity was noted. In pregnant mice dosed subcutaneously with Capsaicin, depletion of substance P in the spinal cord and peripheral nerves of pregnant females and fetuses was noted. In clinical tests, nerve degeneration of intracutaneous nerve fibers and a decrease in pain sensation induced by heat and mechanical stimuli were evident in subjects injected intradermally with Capsaicin. An increase in mean inspiratory flow was reported for eight normal subjects who inhaled nebulized 10(-7) M Capsaicin. The results of provocative and predictive tests involving human subjects indicated that Capsaicin is a skin irritant. Overall, studies suggested that these ingredients can be irritating at low concentrations. Although the genotoxicity, carcinogenicity, and tumor promotion potential of Capsaicin have been demonstrated, so have opposite effects. Skin irritation and other tumor-promoting effects of Capsaicin appear to be mediated through interaction with the same vanilloid receptor. Given this mechanism of action and the observation that many tumor promoters are irritating to the skin, the Panel considered it likely that a potent tumor promoter may also be a moderate to severe skin irritant. Thus, a limitation on Capsaicin content that would significantly reduce its skin irritation potential is expected to, in effect, lessen any concerns relating to tumor promotion potential. Because Capsaicin enhanced the penetration of an anti-inflammatory agent through human skin, the Panel recommends that care should be exercised in using ingredients that contain Capsaicin in cosmetic products. The Panel advised industry that the total polychlorinated biphenyl (PCB)/pesticide contamination should be limited to not more than 40 ppm, with not more than 10 ppm for any specific residue, and agreed on the following limitations for other impurities: arsenic (3 mg/kg max), heavy metals (0.002% max), and lead (5 mg/kg max). Industry was also advised that aflatoxin should not be present in these ingredients (the Panel adopted < or =15 ppb as corresponding to "negative" aflatoxin content), and that ingredients derived from Capsicum annuum and Capsicum Frutescens Plant species should not be used in products where N-nitroso compounds may be formed. (ABSTRACT TRUNCATED)

Cannabinoid modulation of peripheral autonomic and sensory neurotransmission

Cannabinoids are cell membrane-derived signalling molecules that are released from nerves, blood cells and endothelial cells, and have diverse biological effects. They act at two distinct types of G-protein-coupled receptors, cannabinoid CB(1) and CB(2) receptors. Cannabinoid CB(1) receptors are highly localised in the central nervous system and are also found in some peripheral tissues, and cannabinoid CB(2) receptors are found outside the central nervous system, in particular in association with immune tissues. Novel actions of cannabinoids at non-CB(1) non-CB(2) cannabinoid-like receptors and vanilloid VR1 receptors have also recently been described. There is growing evidence that, among other roles, cannabinoids can act at prejunctional sites to modulate peripheral autonomic and sensory neurotransmission, and the present article is aimed at providing an overview of this. Inhibitory cannabinoid CB(1) receptors are expressed on the peripheral terminals of autonomic and sensory nerves. The role of cannabinoid receptor ligands in modulation of sensory neurotransmission is complex, as certain of these (anandamide, an "endocannabinoid", and N-arachidonoyl-dopamine, an "endovanilloid") also activate vanilloid VR1 receptors (coexpressed with cannabinoid CB(1) receptors), which excites sensory nerves and causes a release of sensory neurotransmitter. The fact that the activities of anandamide and N-arachidonoyl-dopamine span two distinct receptor families raises important questions about cannabinoid/vanilloid nomenclature, and as both compounds are structurally related to the archetypal vanilloid capsaicin, all three are arguably members of the same family of signalling molecules. Anandamide is released from nerves, but unlike classical neurotransmitters, it is not stored in and released from nerve vesicles, but is released on demand from the nerve cell membrane. In the central nervous system, cannabinoids function as retrograde signalling molecules, inhibiting via presynaptic cannabinoid CB(1) receptors the release of classical transmitter following release from the postsynaptic cell. At the neuroeffector junction, it is more likely that cannabinoids are released from prejunctional sites, as the neuroeffector junction is wide in some peripheral tissues and cannabinoids are rapidly taken up and inactivated. Understanding the actions of cannabinoids as modulators of peripheral neurotransmission is relevant to a variety of biological systems and possibly their disorders.

Identification of neurones of the brain and spinal cord involved in the innervation of the ductus deferens using the viral tracing method

Using the viral transneuronal tracing technique cell groups of the spinal cord and brain transsynaptically connected with the ductus deferens were identified. Neurotropic (pseudorabies) virus was injected into the muscular coat of the ductus deferens and after survival times of 3, 4 and 5 days the spinal cord and brain were processed immunocytochemically. Virus-labelled neurones could be detected in the preganglionic sympathetic neurones and the dorsal commissural nucleus (upper lumbar segments) and in the sacral parasympathetic nucleus (L6-S1). Virus-infected perikarya were present in several brain stem nuclei including the gigantocellular and paragigantocellular nucleus, the lateral reticular nucleus, the nucleus of the solitary tract, the caudal raphe nuclei, the A1/C1, A2, A5 and A7 noradrenergic cell groups and the locus coeruleus. In the hypothalamus significant numbers of virus-infected neurones could be detected in the paraventricular nucleus. In most cases moderate numbers of virus-labelled cells were present in the lateral hypothalamic area, in the retrochiasmatic area, in the periventricular region and in the median preoptic area. Double-labelling immunofluorescence detection of virus-infected neurones and thyrosine hydroxylase (TH) showed colocalization of virus protein and TH in portion of neurones of the A1/C1, A2, A5 and A7 noradrenergic cell groups, in the locus coeruleus and in the hypothalamic paraventricular nucleus. The present results provide the first morphological data on the multisynaptic circuit of neurones innervating the ductus deferens.

Pharmacological profile of the novel mammalian tachykinin, hemokinin 1

1. The effects of the novel mammalian tachykinin, hemokinin 1 (HEK-1), have been investigated by radioligand binding and functional in vitro and in vivo experiments. 2. Similar to SP (K(i)=0.13 nM), HEK-1 inhibited in a concentration-dependent manner and with high affinity [(3)H]-substance P (SP) binding to human NK(1) receptor (K(i)=0.175 nM) while its affinity for [(125)I]-neurokinin A (NKA) binding at human NK(2) receptor was markedly lower (K(i)=560 nM). 3. In isolated bioassays HEK-1 was a full agonist at tachykinin NK(1), NK(2) and NK(3) receptors. In the rat urinary bladder (RUB) HEK-1 was about 3 fold less potent than SP. In the rabbit pulmonary artery (RPA) HEK-1 and in the guinea-pig ileum (GPI), HEK-1 was about 500 fold less potent than NKA and NKB, respectively. 4. The responses to HEK-1 were antagonized by GR 82334 in RUB (pK(B)=5.6+/-0.07), by nepadutant in RPA (pK(B)=8.6+/-0.04) and by SR 142801 in GPI (pK(B)=9.0+/-0.2) with apparent affinities comparable to that measured against tachykinin NK(1), NK(2) and NK(3) receptor-selective agonists, respectively. 5. Intravenous HEK-1 produced dose-related decrease of blood pressure in anaesthetized guinea-pigs (ED(50)=0.1 nmol kg(-1)) and salivary secretion in anaesthetized rats (ED(50)=6 nmol kg(-1)) with potencies similar to that of SP. All these effects were blocked by the selective tachykinin NK(1) receptor antagonist, SR 140333. 6. We conclude that HEK-1 is a full agonist at tachykinin NK(1), NK(2) and NK(3) receptors, possesses a remarkable selectivity for NK(1) as compared to NK(2) or NK(3) receptors and acts in vivo experiments with potency similar to that of SP.

Molecular determinants of peptide and nonpeptide NK-2 receptor antagonists binding sites of the human tachykinin NK-2 receptor by site-directed mutagenesis

A series of 14 mutants on nine selected residues of the human tachykinin NK(2) receptor was produced and stably transfected into CHO cells to investigate the binding of the peptide MEN 11420 and the nonpeptide SR 48968 antagonists. The main interactions found for MEN 11420 were with Thr171, Tyr206, Tyr266 and Phe270. In the case of SR 48968 crucial residues were Tyr266 and Tyr289. While some overlapping of the binding sites exists, the binding modes suggested by this study appear not to allow structural correlation, and therefore general SAR, between these two antagonists.

The troubled story of tachykinins and neurokinins

A family of peptides that shares a common C-terminal sequence (Phe-X-Gly-Leu-MetNH2) exists in mammalian and non-mammalian species. In mammals, three of these peptides (substance P, neurokinin A and neurokinin B) satisfy the criteria to be considered as neurotransmitters either in the central, peripheral or enteric nervous systems. In addition, multiple receptors for these peptides, which belong to the superfamily of G-protein-coupled receptors, exist. These receptors have distinct pharmacological features and selective agonists and antagonists are available for studying their functional roles. The latest update on nomenclature of these peptides and their receptors, which dates back to 1986, agreed to use the terms tachykinins and tachykinin NK1, NK2 and NK3 receptors. This 'nomenclature mismatch' has generated confusion that urges experts in the field of tachykinin research to provide a revised nomenclature.

Nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in postganglionic parasympathetic nerves innervating the rat vas deferens

Cross-sections of the vas deferens taken from control adult male rats showed positive histochemical reactivity to acetylcholinesterase and immunoreactivity for antibodies to protein gene product 9.5, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, nitric oxide synthase and calcitonin gene-related peptide. Immunoreactivity to substance P was very sparse. Histochemical reactivity to acetylcholinesterase and immunoreactivity to vasoactive intestinal polypeptide and nitric oxide synthase was concentrated in the subepithelial lamina propria and inner smooth muscle layers. Complete surgical denervation resulting from transection of the nerve arising from the pelvic ganglion which supplies the vas deferens totally abolished the immunoreactivity to all of the antibodies tested as well as the histochemical reactivity to acetylcholinesterase. In sections of the prostatic end of the vas deferens taken from rats neonatally pretreated with capsaicin, immunoreactivity to calcitonin gene-related peptide and substance P was reduced by 75 and 83%, respectively. Immunoreactivity to neuropeptide Y, vasoactive intestinal polypeptide and nitric oxide synthase was similar in tissue sections taken from capsaicin-treated rats and those taken from control tissues. Pretreatment of rats with guanethidine or 6-hydroxydopamine decreased immunoreactivity to tyrosine hydroxylase and neuropeptide Y by 60-70%, but immunoreactivity to substance P, vasoactive intestinal polypeptide and nitric oxide synthase was unchanged, while immunoreactivity to calcitonin gene-related peptide and acetylcholinesterase staining was increased by guanethidine but not by 6-hydroxydopamine treatment. Triple labelling experiments showed nitric oxide synthase, vasoactive intestinal polypeptide and acetylcholinesterase all to be co-localized in some nerve fibres. These results indicate that the nitric oxide synthase contained in the nerve fibres innervating the rat vas deferens is unaffected by pretreatment of rats with capsaicin, 6-hydroxydopamine or guanethidine but is abolished by surgical denervation, of postganglionic parasympathetic, sympathetic and sensory nerves. Therefore it appears that nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in the postganglionic parasympathetic nerves which innervate the rat vas deferens.

The tachykinin NK1 receptor. Part I: ligands and mechanisms of cellular activation

The tachykinin NK1 receptor is widely expressed in the mammalian central and peripheral nervous system. Powerful pharmacological tools (agonists and antagonists) are now available to elucidate the physiological role of NK1 receptors at these levels, as well as to understand their role in diseases and establish the possible therapeutic usefulness of NK1 receptor antagonists for treatment of human diseases. The structure-activity studies that have led to the development of potent peptide and non-peptide ligands for the tachykinin NK1 receptor are here reviewed. Among the peptide agonists and antagonists, linear and cyclic sequences have been developed. The non peptide antagonists belong to different chemical classes, i.e. steroids, perhydroisoindolones, quinuclidines, piperidines and tryptophane derivatives. The first non peptide antagonists for NK1 receptors have been obtained by random screening of chemical compounds large collections. The resulting leads were optimized with 'classic' structure activity approaches, aiming at identifying 'common' motifs for interaction with the receptor by ligands of different chemical classes. The results derived from the recent application of molecular biology techniques were useful to drive the design of new ligands toward a precise structural definition of ligand-receptor bi-molecular interactions. Studies on mutant receptors have established that the sites of interaction of peptide agonists and non peptide antagonists with the tachykinin NK1 receptor are largely non overlapping. Moreover, data obtained from mutagenesis of the NK1 receptor further indicate that some amino acid residues in the NK1 receptor sequence are critical for determining the binding affinity of some but not all ligands. Therefore, different antagonists discovered from random screening may not possess common points of interaction or common structural and conformational characteristics for their interaction with the tachykinin NK1 receptor. The tachykinin NK1 receptor couples with G-proteins to determine its biological effects in target cells. Several G-proteins both sensitive (Go, Gi) and insensitive (Gq, G11) to pertussis toxin can mediate the action of NK1 receptors. Moreover, several second messanger signalling systems (elevation of intracellular calcium, stimulation of phosphoinositol turnover, arachidonic acid mobilization, cAMP accumulation) have to be activated following NK1 receptor signalling. Also a direct modulation of certain ion channels at membrane level has been proposed. The NK1 receptor undergoes prompt and significant tachyphylaxis upon exposure to the agonist: this has been shown to be linked with receptor internalization which also occurs physiologically when the NK1 receptor is stimulated by endogenous tachykinins.

Involvement of ATP-sensitive K+ channels in the inhibitory effect of calcitonin gene-related peptide on neurotransmission in rat vas deferens

This study investigated the inhibitory action of human calcitonin-gene-related peptide (CGRP) on neurotransmission in rat isolated vas deferens. The electrically stimulated contractile responses, which were mediated predominantly by activation of postganglionic noradrenergic nerve fibers, were concentration-dependently inhibited by human CGRP (0.1-100 nM, IC50 = 2.15 +/- 0.21 nM, n = 17). Human CGRP at concentrations greater than 3 nM reduced the contractile responses to exogenous noradrenaline and ATP. The inhibitory effect of human CGRP on the electrically stimulated or agonist-induced contractions was antagonized by human CGRP-(8-37), the CGRP receptor antagonist. Glibenclamide (3-10 microM) decreased the effect of human CGRP at a concentration greater than 1 nM whilst glibenclamide did not affect the inhibitory effect of human CGRP on the agonist-induced contractions. These results indicate that human CGRP at low concentrations exerts its inhibitory action mainly by acting on CGRP receptors at the sympathetic nerve terminals supplying rat vas deferens and the activation of ATP-sensitive K+ channels is at least in part involved in the action of human CGRP on neurotransmission.

Pharmacological characterization of the vanilloid receptor in the rat isolated vas deferens

The present study set out to further characterize the vanilloid receptor in the rat isolated vas deferens. In this preparation, both capsaicin and resiniferatoxin (RTX) evoked a concentration-dependent inhibition in the amplitude of electrically-evoked contractions with pEC50 values of 7.62 +/- 0.03 and 12.2 +/- 0.21 respectively. Responses to capsaicin were fast in onset and faded rapidly over a 30-min exposure period, whereas those to RTX were slow in onset and well maintained, an observation believed to reflect pharmacokinetic differences in the rate of penetration to the vanilloid receptor. Responses to both agonists showed mutual cross-desensitization and were antagonized by both the vanilloid-receptor antagonist capsazepine and the ion-channel blocker ruthenium red. The capsaicin analogue, olvanil failed to either mimic or antagonize capsaicin-evoked responses in the rat isolated vas deferens, an effect at variance with previous observations in other tissues. The reason for these differences is unclear, but the possibility of multiple classes of receptor cannot at this stage be ruled out.

The mammalian tachykinin receptors

The tachykinins (TKs) are a family of small peptides which share the common C-terminal sequence Phe-X-Gly-Leu-MetNH2. Three peptides of this family, substance P, neurokinin A and neurokinin B, have an established role as neurotransmitters in mammals. 2. Three receptors for TKs have been cloned: they are G-protein coupled receptors with seven putative transmembrane spanning segments and have been termed NK1 (substance P-preferring), NK2 (neurokinin A-preferring) and NK3 (neurokinin B-preferring). 3. Synthetic agonists are available to selectively stimulate only one receptor, while natural TKs can act as full agonist at each one of the three receptors, albeit at different concentrations. 4. A number of potent and selective antagonists, both peptide and nonpeptide in nature, have recently been developed. 5. The introduction of these ligands has revealed an unforeseen pharmacological heterogeneity of NK1, NK2 and NK3 receptors which appears largely, if not exclusively, linked to the existence of species homologues of the three receptors.

Opposite modulation by tachykinin (NK1) and CGRP receptors of sympathetic control of mouse vas deferens motility

Electrical field stimulation of isolated mouse vas deferens elicited sympathetic twitch whose amplitude was transiently enhanced by the selective tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P (0.3-30 nM), but not by selective NK2 and NK3 receptor agonists. Potentiation by [Sar9,Met(O2)11]substance P was antagonized by (+/-)-CP 96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N- [(2-methoxyphenyl)-methyl]-1-azabicyclo[2.2.2]octan-3-amine] (IC50 = 0.1 microM). On the other hand, electrical field stimulation-induced contractions were inhibited by calcitonin gene-related peptide, CGRP (0.1-30 nM), and this action was reduced by its antagonist, human CGRP-(8-37) (3 microM). [Sar9,Met(O2)11]substance P (3 nM) did not affect either high-K+ or noradrenaline-induced contraction, while CGRP (3 nM) significantly reduced the noradrenaline-induced motor response. Capsaicin (1 microM) inhibited sympathetic twitches, and this effect was partially antagonized by human CGRP-(8-37). In the presence of this antagonist, capsaicin induced a short-living and (+/-)-CP 96,345-sensitive twitch enhancement. These data suggest that the sympathetic control of mouse vas deferens motility can be modulated in an opposite manner by tachykinin NK1 (prejunctionally located) and by CGRP (pre- and/or postjunctionally located) receptors.

Calcium modulatory properties of 2,6-dibutylbenzylamine (B25) in rat isolated vas deferens, cardiac and smooth muscle preparations

1. In rat isolated vas deferens the new compound 2,6-dibutylbenzylamine (B25) evoked a series of repeating rhythmic contractions. Concentration-response curves constructed for this effect were bell-shaped, indicating a biphasic effect for this compound. By contrast, B25 depressed heart contractility without any visible positive inotropic or chronotropic activity. 2. Experiments with tetrodotoxin, reserpine, capsaicin, alpha-adrenoceptor blocking compounds and other agents permit us to exclude a release of neuromediators or a direct stimulation of post-synaptic receptors to account for the rhythmic effect of B25 in the rat vas deferens. 3. In the same tissue, the increase in 45Ca2+ uptake, the voltage-dependency as well as the dependence of the B25-induced rhythmic activity upon the external calcium concentration indicate a direct activation of voltage-sensitive calcium channels (VSCC). 4. Verapamil paradoxically stimulated the rhythmic effect of B25 in the rat vas deferens. La3+ was inactive while nifedipine was a weak inhibitor. By contrast Ni2+ and Mn2+ ions were good inhibitors (IC50 < 10(-4) M), suggesting that a possible opening of T-type VSCC underlies rhythmic effect of B25. 5. In radioligand binding studies competition experiments with [3H]-nitrendipine indicated that only at high concentrations was B25 able to interact with dihydropyridine-sensitive binding sites of heart and vas deferens smooth muscle. 6. B25 (3-30 microM) counteracted the inhibitory effects of omega-conotoxin GVIA in field-stimulated rat vas deferens.

Failure of L-nitroarginine, a nitric oxide synthase inhibitor, to affect hypotension and plasma protein extravasation produced by tachykinin NK-1 receptor activation in rats

1. We have assessed the effect of L-nitroarginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, on hypotension and plasma protein extravasation produced by i.v. administration of substance P (SP) in urethane-anaesthetized rats. 2. I.v. administered SP (1 nmol kg-1) produced maximal blood pressure lowering effect which was not modified by previous administration of L-NOARG (45.6 mumol kg-1 i.v.). The hypotensive response to SP was greatly reduced by the nonpeptide SP antagonist, RP 67,580 (0.68 mumol kg-1) indicating the involvement of tachykinin NK-1 receptor. L-NOARG caused by itself a sustained increase in both systolic and diastolic blood pressure, while RP 67,580 was without effect. 3. I.v. administration of SP produced plasma protein extravasation in the trachea, ureter and urinary bladder (determined by the Evans blue leakage technique). A dose of 10 nmol kg-1 SP was necessary to produce a maximal effect, while the tachykinin NK-1 receptor selective agonist [Sar9]SP sulphone produced a similar maximal response at 3 nmol kg-1 in the various organs tested. 4. L-NOARG failed to affect plasma protein extravasation produced by either SP or [Sar9]SP sulphone while RP 67,580 inhibited the response to both agents. 5. The present findings fail to reveal a significant contribution of NO production in the hypotensive and inflammatory response to NK-1 receptor stimulation in urethane-anaesthetized rats.

In vivo and in vitro pharmacology of SR 48,968, a non-peptide tachykinin NK2 receptor antagonist

The activity of SR 48,968, a novel non-peptide antagonist of tachykinin NK2 receptors was evaluated in vitro in several bioassays for the NK2 receptor (rabbit pulmonary artery, rabbit bronchus, hamster trachea, rat vas deferens) and compared to that of the peptide antagonists, MEN 10,376, L 659,877 and MDL 29,913. SR 48,968 behaved as a potent and competitive antagonist in the four isolated preparations (pA2 values between 8.3 and 9.6 in different preparations), being more potent (about 10 times) in the rabbit pulmonary artery and rabbit bronchus than in the hamster trachea or rat vas deferens. The antagonistic profile of SR 48,968 resembled that of MEN 10,376, and contrasted with those of L 659,877 and MDL 29,913 which were distinctly more potent on the hamster trachea and rat vas deferens. In vivo, SR 48,968 (0.1 mumol/kg i.v.) blocked the contraction of rat urinary bladder stimulated by [beta Ala8]neurokinin A-(4-10) (NK2 receptor agonist) without affecting that produced by [Sar9]substance P sulfone (NK1 receptor agonist). The hypotension and salivary secretion produced by the latter agonist were not modified by SR 48,968. In contrast, (+/-)-CP 96,345 (10 mumol/kg i.v.) blocked bladder contraction, salivary secretion and hypotensive responses elicited by the NK1 receptor agonist while leaving unaffected the bladder contraction produced by the NK2 receptor agonist. SR 48,968 is a potent and competitive antagonist of the tachykinin NK2 receptor with a limited but distinct ability to discriminate between putative subtypes/species variants of the NK2 receptor. The high potency and selectivity of SR 48,968 make this novel compound an important tool for studying the distribution and function of tachykinin NK2 receptors.

A comparison of capsazepine and ruthenium red as capsaicin antagonists in the rat isolated urinary bladder and vas deferens

1. The ability of capsazepine, a recently developed capsaicin receptor antagonist, to prevent the effects of capsaicin on the rat isolated urinary bladder (contraction) and vas deferens (inhibition of electrically-evoked twitches) was compared to that of ruthenium red, a dye which behaves as a functional antagonist of capsaicin. 2. In the rat bladder, capsazepine (3-30 microM) produced a concentration-dependent rightward shift of the curve to capsaicin without any significant depression of the maximal response to the agonist. By contrast, ruthenium red (10-30 microM) produced a non-competitive type of antagonism, characterized by marked depression of the maximal response attainable. Similar findings were obtained in the rat isolated vas deferens in which capsazepine (10 microM) produced a rightward shift of the curve to capsaicin while ruthenium red (3 microM) depressed the maximal response to the agonist. 3. At the concentrations used to block the effect of capsaicin, neither capsazepine nor ruthenium red affected the contractile response of the rat urinary bladder produced by either neurokinin A or electrical field stimulation or the twitch inhibition produced by rat alpha-calcitonin gene-related peptide (alpha CGRP) in the vas deferens. 4. These findings provide additional evidence that both capsazepine and ruthenium red are valuable tools for exploration of the function of capsaicin-sensitive primary afferent neurones. The antagonism of the action of capsaicin by capsazepine is entirely consistent with the proposed interaction of this substance with a vanilloid receptor located on primary afferents, while the action of ruthenium red apparently involves a more complex, non-competitive antagonism.

Human alpha-calcitonin gene-related peptide-(8-37) as an antagonist of exogenous and endogenous calcitonin gene-related peptide

The C-terminal fragment of the human alpha-calcitonin gene-related peptide (hCGRP), hCGRP-(8-37) competitively antagonized both the positive inotropic effect of hCGRP in the guinea-pig isolated left atria (pA2 6.89) and the smooth muscle relaxant effect of hCGRP in the rat isolated vas deferens (pA2 6.55) but left the response to isoprenaline unaffected in both preparations. In addition, hCGRP-(8-37) reduced the responses produced by activation of the 'efferent' function of capsaicin-sensitive primary afferents in both preparations thus providing pharmacological evidence for the involvement of endogenous CGRP. hCGRP-(8-37) appears a useful tool to establish the physiological role of CGRP in peripheral preparations from different species.

The neurotransmitter role of calcitonin gene-related peptide in the rat and guinea-pig ureter: effect of a calcitonin gene-related peptide antagonist and species-related differences in the action of omega conotoxin on calcitonin gene-related peptide release from primary afferents

In the rat and guinea-pig isolated ureter electrical field stimulation of intrinsic nerves (10 Hz for 10 s) produces transient inhibition of evoked (20 mM KCl or 0.1-1 microM neurokinin A) rhythmic contractions by releasing transmitter(s) from peripheral endings of capsaicin-sensitive primary afferents. The C-terminal fragment of human calcitonin gene-related peptide (8-37) blocked the inhibitory effect of electrical field stimulation as well as that produced by exogenous calcitonin gene-related peptide, while leaving unaffected the inhibitory response to isoprenaline. Human calcitonin gene-related peptide (8-37) was devoid of any inhibitory activity of its own but enhanced the amplitude and frequency of KCl-evoked rhythmic contractions in the rat ureter, probably by antagonizing the inhibitory effect of endogenous calcitonin gene-related peptide released by KCl. Omega conotoxin fraction GVIA, a peptide which possesses a potent blocking activity of N-type voltage-sensitive calcium channels, prevented the inhibitory response to electrical stimulation in the guinea-pig ureter, while leaving the response unaffected in the rat ureter. Conotoxin had no effect toward the inhibition produced by exogenous calcitonin gene-related peptide indicating its prejunctional site of action, demonstrated previously in the guinea-pig ureter [Maggi et al. (1990) Neurosci, Lett. 114, 203-206]. Dermorphin, an amphibian peptide with potent agonist activity on mu-type opioid receptors, inhibited the response to electrical stimulation in the guinea-pig ureter but had no effect in the rat ureter.(ABSTRACT TRUNCATED AT 250 WORDS)

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

We investigated the effect of calcitonin-gene-related peptide (CGRP) on bladder contractions and penile erection in 12 dogs. In a system in which the arteries were tied bilaterally to ensure delivery of high drug levels to the bladder, arterial injections of CGRP significantly reduced the peak intravesical pressure of bladder contractions induced by pelvic nerve stimulation or arterial injection of carbachol. When given intravenously, CGRP had no effect on bladder contractions consequent to neural stimulation. Intravesical instillation of CGRP, however, reduced the bladder contractions significantly. Histologic staining showed CGRP-immunoreactive nerve fibers within the smooth muscle layers of the bladder wall. Intracavernous CGRP increased cavernous arterial flow and induced cavernous smooth muscle relaxation and venous outflow occlusion. Muscarinic blockade had no effect on the canine intracavernous pressure response to intracavernous injection of CGRP. Histologic staining for CGRP-immunoreactivity showed nerve-fiber-like staining within the cavernous arterial wall, the nerves running near the cavernous arteries, and the cavernous smooth muscles. Our results suggest a possible role for CGRP in the regulation of the smooth muscle tone of the bladder and penis.

Modulation of neurotransmission in the guinea-pig vas deferens by capsaicin: involvement of calcitonin gene-related peptide and substance P

1. The effects of capsaicin, calcitonin gene-related peptide and substance P were studied via three parameters in the guinea-pig vas deferens: the overflow of ATP and of tritiated noradrenaline, the mechanical responses to field stimulation and the mechanical responses to exogenous noradrenaline and alpha, beta-methylene ATP. 2. At 2 Hz, capsaicin inhibited the stimulus-evoked release of ATP, whereas it was without effect on the release of noradrenaline. At 20 Hz capsaicin did not affect the release of either of the cotransmitters. Capsaicin enhanced responses to alpha, beta-methylene ATP, but not to exogenous noradrenaline. 3. Calcitonin gene-related peptide, like capsaicin, inhibited the release of ATP, but not noradrenaline at 2 Hz and was without effect on release at 20 Hz. However, calcitonin gene related peptide inhibited responses to alpha, beta-methylene ATP and was without effect on responses to exogenous noradrenaline. 4. Substance P had no effect on the release of either noradrenaline or ATP at either frequency. However, like capsaicin it enhanced responses to alpha, beta-methylene ATP and was without effect on exogenous noradrenaline. 5. These results suggest that the actions of capsaicin on the guinea-pig isolated vas deferens are mediated via the release of both calcitonin gene-related peptide and substance P. Furthermore, as capsaicin and calcitonin gene-related peptide prejunctionally modulate purinergic, but not noradrenergic transmission, this suggests that the mechanisms for the storage and release of the sympathetic co-transmitters noradrenaline and ATP may not be the same.

Regional differences in the motor response to capsaicin in the guinea-pig urinary bladder: relative role of pre- and postjunctional factors related to neuropeptide-containing sensory nerves

Capsaicin induced a contraction of isolated strips from the guinea-pig urinary bladder which was more evident in the dome than in the neck and inhibited contractions induced by field stimulation, particularly in the neck. Both responses exhibited prompt desensitization and were tetrodotoxin-resistant, suggesting a specific action on transmitter release from sensory nerve terminals. Indeed, the contractile response in the dome was prevented by a substance P antagonist while the inhibitory response in the neck was prevented by immunoblockade with anticalcitonin gene-related peptide (CGRP) serum. Substance P produced a contraction of the guinea-pig bladder, being about 5 times more potent in the dome than in the neck, while CGRP inhibited the evoked contractions, being about 8 times more potent in the neck than in the dome. Further, the maximal effect of CGRP in the neck was almost double that in the dome. Substance P- and CGRP-like immunoreactivity were detected in both the dome and the neck with no regional differences for each peptide. CGRP-like immunoreactivity was 6.3 and 7.9 times higher than substance P-like immunoreactivity in the dome and the neck, respectively. Exposure to capsaicin evoked release of both substance P- and CGRP-like immunoreactivity from the dome and the neck. Peak CGRP-like immunoreactivity released by capsaicin was 12.3 and 8 times greater than substance P-like immunoreactivity in the dome and the neck, respectively. For each peptide, no difference was found in peak release in the dome vs neck. Total substance P-like immunoreactivity released from the neck was 25% lower than that released from the dome. The ability of CGRP to stimulate accumulation of 3',5' cyclic adenosine monophosphate in membranes prepared from the bladder muscle was greater in preparations from the neck than from the dome. These findings indicate that postjunctional mechanisms (type and number of receptors for sensory neuropeptides, coupling with second messengers) are a major determinant of the type of motor responses consequent of the release of sensory neuropeptides from capsaicin-sensitive nerves.

The antagonism induced by ruthenium red of the actions of capsaicin on the peripheral terminals of sensory neurons: further studies

Ruthenium Red, an inorganic dye which blocks transmembrane calcium (Ca) fluxes in neural tissues, reduced the capsaicin-induced release of substance P-like immunoreactivity from muscle strips of the guinea-pig urinary bladder in a concentration-dependent (30 nM - 3 microM) manner, and protected the sensory fibers from capsaicin-induced densensitization. A similar antagonism of the actions of capsaicin was observed in functional experiments (capsaicin-induced contraction of the isolated guinea-pig bladder or inhibition of twitches of the isolated rat vas deferens). In view of its established action on the depolarization-coupled entry of Ca into synaptosomes and the secretion of transmitter, we propose that Ruthenium Red could antagonize the action of capsaicin on the peripheral terminals of sensory nerves by a similar mechanism, thereby suppressing transmitter secretion and preventing the establishment of desensitization.

Several neuropeptides determine the visceromotor response to capsaicin in the guinea-pig isolated ileal longitudinal muscle

Capsaicin (1 microM) produced, after an initial contraction, a depression of the field stimulation-induced contraction of the guinea-pig isolated ileal longitudinal muscle. Both effects exhibited prompt desensitization, indicating the involvement of a specific action on sensory nerves. The initial contraction was inhibited by [D-Pro4,D-Trp7,9,Phe11]SP-(4-11), a substance P (SP) antagonist, which did not affect the inhibitory component of the response. Incubation of the strips with antiCGRP (CGRP = calcitonin gene-related peptide) serum did not modify the amplitude of the capsaicin-induced contraction but inhibited the twitch depression induced by capsaicin. AntiCGRP serum blocked the effects of exogenous CGRP but not the inhibitory response induced by baclofen. These findings provide evidence that the release of several neuropeptides from sensory nerves determines the visceromotor response to capsaicin in this preparation. In particular, a CGRP-like peptide could be responsible for the inhibitory phase which follows the initial contraction which is due to release of SP and/or related peptides.