Bovine Retractor Penis Muscle Research Articles

Endothelium Dependent Relaxation in Rabbit Genital Resistance Arteries is Predominantly Mediated by Endothelial-Derived Hyperpolarizing Factor in Females and Nitric Oxide in Males

In nongenital arteries a sex difference has been postulated in the dominant endothelium-derived relaxant factor(s), eg nitric oxide, prostacyclin or endothelial-derived hyperpolarizing factor. Knowledge of endothelium-derived relaxant factor mechanisms in genital tissues could influence the development of novel treatments for sexual dysfunction. We compared nitric oxide and endothelial-derived hyperpolarizing factor contributions to acetylcholine induced relaxation in the genital arteries of the 2 sexes. Male dorsal and cavernous penile arteries, and female extravaginal and intravaginal arteries from New Zealand White rabbits were studied. Acetylcholine concentration-vasodilator response curves were constructed in the presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester, K(+) channel blockers (apamin and charybdotoxin) or a combination. Indomethacin was present throughout to exclude prostacyclins. Extravaginal artery relaxation was predominantly endothelial-derived hyperpolarizing factor induced. Apamin plus charybdotoxin decreased maximal relaxations from a mean +/- SEM of 77% +/- 4% to 23% +/- 3% in 6 preparations (p <0.01). However, nitric oxide and endothelial-derived hyperpolarizing factor contributed to overall function. Dorsal artery relaxation was largely nitric oxide induced. Nomega-nitro-L-arginine methyl ester decreased maximal relaxations from 90% +/- 3% to 41% +/- 9% (p <0.001) with no endothelial-derived hyperpolarizing factor involvement (p >0.05). In cavernous and intravaginal arteries nitric oxide and endothelial-derived hyperpolarizing factor contributed to acetylcholine induced relaxation, while nitric oxide predominated. Blocking nitric oxide synthase or K(+) channels indicated that myogenic tone and constitutive activity of endothelium-derived relaxant factors were present. Vasodilator nerve mediated responses were influenced by each with the former more effective. Vaginal inflow arteries showed a dominance of endothelial-derived hyperpolarizing factor, contrasting with nitric oxide in penile arteries. Penile arteries followed the trend that endothelial-derived hyperpolarizing factor involvement increased with decreasing vessel caliber, while the reverse was demonstrated in female arteries.

Role of catalase in the smooth muscle relaxant actions of sodium azide and cyanamide

The aim of this study was to determine the role of catalase in the smooth muscle relaxant actions of sodium azide and cyanamide. The effects of 3-amino-1,2,4-triazole suggested a role for this enzyme in the relaxant actions of sodium azide on rat aorta and bovine retractor penis muscle and cyanamide on rat aorta. Moreover, results obtained using a difference spectrophotometric assay based upon the oxidation of haemoglobin were consistent with the catalase-dependent oxidation of sodium azide to nitric oxide (NO) and of cyanamide to nitroxyl anion. Surprisingly, however, no free nitric oxide or nitroxyl was detected in solution using a sensitive electrode. This anomaly might be explained if the stable complexes of catalase with nitric oxide or nitroxyl do not release their respective ligand except to sites of high affinity, such as the haemoglobin employed in the difference spectrophotometric assay, or indeed, the soluble guanylate cyclase within the smooth muscle.

The endothelin ET(B) receptor agonist [125I]BQ-3020 binds predominantly to nerves in the bovine retractor penis muscle and penile artery.

Preliminary pharmacological experiments have suggested that in the bovine retractor penis muscle there are relaxation-mediating endothelin ET(B) receptors, at least part of which are located on the inhibitory nitrergic nerves. The present work was undertaken to test this hypothesis by means of receptor autoradiography and additional pharmacological experiments. In the retractor penis muscle and the penile artery, specific binding of the ETB receptor-selective agonist [125I]BQ-3020 took place predominantly to nerve trunks and minor nerve branches. The situation was the same in the dorsal metatarsal artery, that was included as a reference because of its different innervation. Throughout the nerves the silver grains were evenly distributed over the nuclei of Schwann cells and the spaces between them. In the retractor penis there was also a small amount of specific binding to smooth muscle. No specific endothelial binding was observed in any of the tissues examined. The pharmacological studies confirmed that the relaxation of the retractor penis muscle induced by the ET(B) receptor-selective agonist, sarafotoxin S6c, is susceptible to tetrodotoxin as well as to inhibition of nitric oxide synthase. The relaxation was also characterized by inconsistency, weakness and tachyphylaxis. The electrical field stimulation-induced submaximal relaxation of the retractor penis was unaffected by stimulation or blockade of ET(B) receptors. The autoradiography suggests that in all the three bovine tissues studied there are ET(B) receptors located on nerves independently of the type of efferent nerve. The pharmacological experiments do not support the concept that in the bovine retractor penis muscle neuronal ET(B) receptors exert important immediate effects on the functioning of the penile erection-mediating nitrergic nerves.

The Endothelin ETB Receptor Agonist [125I]BQ‐3020 Binds Predominantly to Nerves in the Bovine Retractor Penis Muscle and Penile Artery

Abstract:Preliminary pharmacological experiments have suggested that in the bovine retractor penis muscle there are relaxation‐mediating endothelin ETB receptors, at least part of which are located on the inhibitory nitrergic nerves. The present work was undertaken to test this hypothesis by means of receptor autoradiography and additional pharmacological experiments. In the retractor penis muscle and the penile artery, specific binding of the ETB receptor‐selective agonist [125I]BQ‐3020 took place predominantly to nerve trunks and minor nerve branches. The situation was the same in the dorsal metatarsal artery, that was included as a reference because of its different innervation. Throughout the nerves the silver grains were evenly distributed over the nuclei of Schwann cells and the spaces between them. In the retractor penis there was also a small amount of specific binding to smooth muscle. No specific endothelial binding was observed in any of the tissues examined. The pharmacological studies confirmed that the relaxation of the retractor penis muscle induced by the ETB receptor‐selective agonist, sarafotoxin S6c, is susceptible to tetrodotoxin as well as to inhibition of nitric oxide synthase. The relaxation was also characterized by inconsistency, weakness and tachyphylaxis. The electrical field stimulation‐induced submaximal relaxation of the retractor penis was unaffected by stimulation or blockade of ETB receptors. The autoradiography suggests that in all the three bovine tissues studied there are ETB receptors located on nerves independently of the type of efferent nerve. The pharmacological experiments do not support the concept that in the bovine retractor penis muscle neuronal ETB receptors exert important immediate effects on the functioning of the penile erection‐mediating nitrergic nerves.

No colocalization of immunoreactivities for VIP and neuronal NOS, and a differential relation to cGMP-immunoreactivity in bovine penile smooth muscle

The distribution of immunoreactivity (IR) for the neuropeptide vasoactive intestinal polypeptide (VIP) and neuronal nitric oxide synthase (nNOS) in the bovine retractor penis muscle (RP) and penile artery (PA) was studied by using two different methods. The distribution of these immunoreactivities was also compared with that of the immunoreactivity for cyclic guanosine monophosphate (cGMP). In both tissues the nerve fibers and terminals immunoreactive for VIP had a distribution that was completely different from that of the nerve fibers and terminals immunoreactive for nNOS. This contrasts with the previous observations in penile smooth muscle of other species. In the RP, as well as in the PA, many of the VIP-IR fibers were also immunoreactive for neurofilaments (NF), whereas the nNOS-IR fibers were consistently devoid of NF-IR. Stimulation with sodium nitroprusside, a nitric oxide donor, considerably increased cGMP-IR in the smooth muscle cells in both RP and PA, and in several nerve fibers in PA. Many of these cGMP-IR nerve fibers exhibited nNOS-IR, whereas none of them was immunoreactive for VIP. Our results suggest that the degree of coexistence of VIP-IR and nNOS-IR in the nerve fibers and terminals innervating penile smooth muscle show wide species differences. They also suggest that the mechanisms by which VIP could be involved in neurogenic penile erection may vary between species.

Inhibition of nitrergic neurotransmission in the bovine retractor penis muscle by an oxidant stress: effects of superoxide dismutase mimetics.

1. A number of superoxide dismutase (SOD) mimetics were examined both biochemically for their ability to inhibit the superoxide-catalyzed reduction of cytochrome c and nitro blue tetrazolium, and functionally for their ability to mimic authentic Cu/Zn SOD in restoring nitrergic neurotransmission in bovine retractor penis (BRP) muscle following its inhibition by oxidant stress. 2. The SOD mimetics investigated were CuSO4, MnCl2, CuDIPS (copper [II] [diisopropylsalicylate]2), MnTBAP (manganese [III] tetrakis 4-benzoic acid porphyrin), MnTMPyP (manganese [III] tetrakis 1-methyl-4-pyridyl porphyrin pentachloride), tiron (4,5-dihydroxy-1,3-benzene disulphonic acid), PTIYO (4-phenyl,2,2,5,5,-tetramethyl-3-imidazolin-1-yloxy-3-oxide) and tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl). 3. The rank order of potency in inhibiting the reduction of cytochrome c was: CuSO4 > or = MnCl2 > or = CuDIPS > or = MnTMPyP > MnTBAP > tempol > or = tiron > PTIYO. 4. The requirement for EDTA (0.1 mM) prevented assessment of the activity of CuSO4, MnCl2 and CuDIPS in the assay involving inhibition of reduction of nitro blue tetrazolium. However, the rank order of potency for those agents which could be examined (MnTMPyP > MnTBAP > tiron > or = tempol > PTIYO) was essentially similar to that seen in the cytochrome c assay. 5. Inhibition of endogenous Cu/Zn SOD with diethyldithiocarbamate (DETCA, 3 mM, 120 min) in BRP muscle strips, followed by addition of the superoxide anion generator, LY 83583 (1 microM), resulted in almost complete abolition of nitrergic relaxation (4 Hz, 10 s). 6. Authentic Cu/Zn SOD (1-300 u ml(-1)), CuSO4 (0.1-300 microM), MnCl2 (0.1-100 microM) and MnTMPyP (10-300 microM) each restored nitrergic transmission by around 50%. However, CuDIPS (0.1-30 microM), MnTBAP (0.1-100 microM), tempol (10 microM - 3 mM), PTIYO (1-300 microM) and tiron (10 microM - 10 mM) all failed to restore nitrergic transmission. 7. The ability of MnTMPyP to restore nitrergic neurotransmission may therefore provide a lead in the development of SOD mimetics as therapeutic agents in the treatment of neuropathies associated with oxidant stress.

Effects of hydroxocobalamin on nitrergic transmission in rat anococcygeus and bovine retractor penis muscles: sensitivity to light

Hydroxocobalamin inhibited nitrergic nerve-induced relaxations in rat anococcygeus and bovine retractor penis muscles in a concentration-dependent manner. In the rat anococcygeus muscle, the inhibition was greater in light than in dark conditions, whereas in the bovine retractor penis the inhibition was similar under both conditions. © 1997 Elsevier Science B.V. All rights reserved.

P2.26 Neuronal localization of ET B-receptors in the bovine retractor penis muscle : U-M Parkkisenniemi ∗, 1, A Palkama 2 & E Klinge 1, 1Dept. of Pharmacy, POB 56; 2Dept. of Anatomy, POB 9; FIN-00014 Univ. of Helsinki

P2.26 Neuronal localization of ET B-receptors in the bovine retractor penis muscle : U-M Parkkisenniemi ∗, 1, A Palkama 2 & E Klinge 1, 1Dept. of Pharmacy, POB 56; 2Dept. of Anatomy, POB 9; FIN-00014 Univ. of Helsinki

Functional characterization of endothelin receptors in the bovine retractor penis muscle and penile artery.

The effects of endothelin-1 and sarafotoxin 6c on the bovine retractor penis muscle and the bovine penile artery were studied, and a functional characterization of endothelin receptors in these tissues was performed by using the ETA-receptor antagonist BQ-123 and the ETB-receptor antagonist IRL 1038. The retractor penis muscle and the penile artery were about equipotently contracted by endothelin-1 in a concentration-dependent manner the EC50 values being 3.5 x 10(-9) M and 1.3 x 10(-9) M, respectively. In both tissues BQ-123 (10(-6) M) inhibited maximal contraction induced by endothelin-1 by about 50%. Sarafotoxin 6c substantially relaxed the retractor penis muscle, and to a lesser extent also the penile artery, whereas endothelin-1 did not relax either tissue. The sarafotoxin 6c-induced relaxation of the retractor penis muscle was totally inhibited by IRL 1038 (3 x 10(-6) M) and the nitric oxide synthase inhibitor L-NNA (10(-4) M). In both tissues L-NNA enhanced the contraction induced by endothelin-1 and lowered the threshold concentration for it. The results show that in both tissues the contraction induced by endothelin-1 was mediated primarily by ETA-receptors. The retractor penis muscle is also equipped with ETB-receptors, probably at least in part located on the inhibitory nerves, which mediate relaxation via activation of the L-arginine nitric oxide synthase pathway.

Blockade of nitrergic transmission by hydroquinone, hydroxocobalamin and carboxy‐PTIO in bovine retractor penis: role of superoxide anion

1. The effects of inhibiting endogenous Cu/Zn superoxide dismutase (SOD) with diethyldithiocarbamate (DETCA) were examined on the ability of hydroquinone, hydroxocobalamin and carboxy-PTIO to block nitrergic relaxation in the bovine retractor penis (BRP) muscle. 2. Incubation of strips of BRP with DETCA (3 mM) for 2 h reduced SOD activity from 73.1 +/- 15.7 to 8.2 +/- 1.9 units mg-1 protein. 3. Hydroquinone (10 microM--1 mM) produced weak inhibition of nitrergic (4 Hz, 10 s) relaxation in control strips of BRP, but powerful inhibition in strips treated with DETCA (3 mM, 2 h). Exogenous SOD (250 units ml--1) produced a partial blockade of the ability of hydroquinone to inhibit nitrergic relaxation in DETCA-treated strips. 4. In an assay of SOD-inhibitable reduction of cytochrome C, hypoxanthine (0.1 mM)/xanthine oxidase (16 munits ml-1) and pyrogallol (10 microM), led to the rapid generation of superoxide anion. Hydroquinone (10 microM) also led to the generation of the free radical, although the rate of generation was slower. 5. Two NO-scavenging agents, hydroxocobalamin (0.1 microM--1 mM) and carboxy-PTIO (0.1-1 mM), produced concentration-dependent blockade of nitrergic relaxation of the BRP. The magnitude of the blockade induced by these agents was unaffected following treatment with DETCA or SOD. 6. The findings with hydroquinone support our previous proposal that endogenous Cu/Zn SOD plays a vital role in protecting nitrergic neurotransmission from inactivation by superoxide anion. Results with hydroxocobalamin and carboxy-PTIO are consistent with the known ability of these agents to scavenge NO. The nitrergic neurotransmitter in the BRP thus appears to have the properties of NO.

NANC neurotransmission in the bovine retractor penis muscle is blocked by superoxide anion following inhibition of superoxide dismutase with diethyldithiocarbamate

This study examined the effects of inhibiting Cu/Zn Superoxide dismutase with diethyldithiocarbamate (DETCA) on the ability of Superoxide generating agents such as pyrogallol, hypoxanthine/xanthine oxidase and LY 83583, to influence NANC relaxation of strips of bovine retractor penis (BRP) muscle. Although pyrogallol (100 μM) and hypoxanthine (0.3 mM)/xanthine oxidase (64 mU ml −1) had little effect on NANC relaxation in control strips, both induced almost complete inhibition following treatment with DETCA (3 mM) for 1 h. Inhibition was due to the actions of Superoxide anion since it was blocked by the addition of exogenous Superoxide dismutase (250 U ml −1). LY 83583 (0.1–30 μM) produced a concentration-dependent inhibition of NANC relaxation even in control strips and this too was blocked by exogenous Superoxide dismutase, but sensitivity to inhibition was enhanced 10-fold following treatment with DETCA. The data suggest that under normal circumstances the NANC neurotransmitter is protected by high levels of tissue Superoxide dismutase, and inhibition of this enzyme increases its susceptibility to destruction by Superoxide anions. An important impediment to accepting free nitric oxide as the NANC neurotransmitter in the BRP on the basis that Superoxide anion-generating agents inhibit the actions of authentic nitric oxide but not those of NANC nerve stimulation has thus been removed.

Relaxation of the bovine retractor penis muscle by a small K + excess and the role of K + in its neurogenic relaxation

The mechanism of the relaxation of the bovine retractor penis muscle induced by 6.7 mM K + as well as the role of K + in the neurogenic relaxation of this muscle induced by nicotine, acetylcholine or electrical field stimulation, was studied. The relaxation induced by 6.7 mM K + was, contrary to that induced by nicotine or electrical field stimulation, abolished by 10 −7 M ouabain. 15 min exposure to 10 −5 M N G-nitro- L-arginine 3.2 × 10 −6 M tetrodotoxin, 5.0 × 10 −4 M hexamethonium, 5.3 × 10 −4 M methylene blue or hypoxia, all known to inhibit the neurogenic relaxation, did not affect the relaxation induced by 6.7 mM K +, which was also unaffected by 10 −5 M apamin, 3 × 10 −3 M 4-aminopyridine, 2.6 × 10 −2 M tetraethylammonium and 7.3 × 10 −4 M Ba 2+. Exposure to K +-free solution reversibly abolished the neurogenic relaxations. The relaxations caused by 5.0 × 10 −7 M cromakalim and 2.0 × 10 −6 M pinacidil were totally blocked by 10 −5 M glibenclamide. Glibenclamide and apamin did not affect the tone of the muscle or its neurogenic relaxations. 4-Aminopyridine 4.0 × 10 −5 to 3.0 × 10 −3 M and tetraethylammonium 10 −4 to 2.6 × 10 −2 M raised the tone and enhanced the relaxations elicited by electrical field stimulation. The results indicate that the relaxation induced by 6.7 mM K + is partly mediated by activation of Na +-K + ATPase and that its mechanism is thoroughly different from that of the neurogenic relaxations. K + channels sensitive to cromakalim and pinacidil exist in the smooth muscle cells of the bovine retractor penis, but they or small conductance K + channels are not involved in its neurogenic relaxation. The effects of the inhibitory neurotransmitter(s) on the smooth muscle cells are not mediated by K + channels sensitive to 4-aminopyridine or tetraethylammonium, but such neuronal K + channels may participate in the regulation of release of the inhibitory transmitter(s).

Non‐adrenergic, non‐cholinergic relaxation of the bovine retractor penis muscle: role of S‐nitrosothiols

1. This study examined the possibility that an S-nitrosothiol, rather than nitric oxide, functions as the non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the bovine retractor penis (BRP) muscle. 2. Treatment of BRP muscle with either of two sulphydryl inactivating agents, diamide (1 mM) and N-ethylmaleimide (0.3 mM), inhibited NANC relaxation and this was prevented by pretreating tissues with L-cysteine (3 mM), L-glutathione (3 mM) or dithiothreitol (3 mM). Inhibition was not specific, however, since the inactivating agents also inhibited the relaxant actions of authentic nitric oxide (0.3 microM), glyceryl trinitrate (0.001-1 microM) and isoprenaline (0.01-1 microM). 3. Reacting nitric oxide with L-cysteine in nominally oxygen-free solution at pH 3, followed by purging to remove free nitric oxide and neutralisation, produced greater and more prolonged relaxant activity when assayed on rabbit aortic rings than could be attributed to nitric oxide alone. H.p.l.c. analysis of the mixture identified a new peak distinct from either L-cysteine or nitric oxide which was responsible for the relaxant activity. The spectral absorption of this new compound had two bands with peaks at 218 and 335 nm. 4. Using a series of structural analogues of L-cysteine (all at 15 mM) it was found that removal of the carboxyl group (L-cysteamine), replacement of the carboxyl with an ester function (L-cysteine methyl ester) or substitution at the amino group (N-acetyl-L-cysteine) had no effect on the ability to generate relaxant activity upon reaction with nitric oxide (0.1 mM). In contrast, substitution at the sulphydryl group (S-methyl-L-cysteine, L-cysteinesulfinic acid and L-cysteic acid), or formation of disulphides(L-cystine and L-cystamine) led to a complete loss of ability to generate relaxant activity. L-Glutathione was also able to react with nitric oxide to produce relaxant activity, and this too was blocked upon substitution of the free sulphydryl group (S-methyl-L-glutathione). A free sulphydryl group was therefore required to generate relaxant activity following reaction with nitric oxide.5. Reacting L-cysteine (10 mM) with nitric oxide (~ 3 mM) under more stringent oxygen-free conditions followed by purging to remove free nitric oxide resulted in the generation of low relaxant activity and small absorption peaks at 218 and 335 nm and these were unaffected upon exposure to the air. In contrast, admitting air to the reaction chamber before purging enhanced both relaxant activity and the absorption peaks at 218 and 335 nm by some 40 fold and the solution turned pink due to the appearance of another absorption peak at 543 nm. This enhanced relaxant activity was not due to nitrogen dioxide being the reactive species, since at 0.1 mM this gas failed to react with L-cysteine to generate relaxant activity, and at 1 mM generated less activity than the equivalent concentration of nitricoxide.6. The relaxant activity generated by reacting nitric oxide with L-cysteine or L-glutathione was abolished following treatment with haemoglobin (3 MicroM), methylene blue (10 MicroM) or Nmethylhydroxylamine(100 MicroM), but was unaffected by N0-nitro-L-arginine (30 MicroM). Furthermore, two agents that generate superoxide anion, pyrogallol (0.1 mM) and hydroquinone (0.1 mM), also inhibited this relaxant activity as well as that induced by authentic nitric oxide (0.3 MicroM) but as previously reported, had no effect on relaxation induced by NANC nerve stimulation. Superoxide dismutase(100 u ml1) reversed the actions of pyrogallol and hydroquinone but had no effect on NANC relaxation.7. In conclusion, the reaction of nitric oxide with L-cysteine or L-glutathione generates relaxant activity which exceeds that of nitric oxide alone and probably results from formation of S-nitrosocysteine and S-nitrosoglutathione, respectively. The effects of pyrogallol and hydroquinone suggest that the NANCneurotransmitter is a superoxide anion-resistant, nitric oxide-releasing molecule and that neither S-nitrocysteine nor S-nitrosoglutathione is a suitable candidate for this.

The use of the bovine retractor penis muscle for the assessment of ganglion-blocking activity of neuromuscular blocking and other drugs

Inhibition of relaxation of strips of the bovine retractor penis muscle induced by a standard dose of nicotine (30 μm) was used for quantitative assessment of the ganglion-blocking activity of eight neuromuscular blocking agents that are in clinical use. The order of potency of the drugs studied was (+)-tubocurarine alcuronium vecuronium metocurine pancuronium atracurium ⋙ suxamethonium gallamine. The results have been compared to those obtained with other methods. On the basis of the present results, it is concluded that inhibition of the nicotine-induced relaxation of the bovine retractor penis muscle can be used as an alternative, sensitive in vitro method for the assessment of the ganglion-blocking activity of a neuromuscular blocking agent relative to that of, for example, (+)-tubocurarine. Earlier results have showed that this method is useful also for the assessment of the ganglion-blocking activity of other drugs, because it has yielded comparable and reproducible results at the quantitation of this property of actual ganglion-blocking and various antimuscarinic agents. In addition, this method may be useful for rapid screening of ganglion-blocking activity.

Characterization and localization of nitric oxide synthase in non-adrenergic non-cholinergic nerves from bovine retractor penis muscles.

1. Partially purified soluble nitric oxide (NO) synthase was isolated from the bovine retractor penis muscle (BRP), a tissue in which the inhibitory response to non-adrenergic non-cholinergic nerve (NANC) stimulation appears to be mediated by NO or NO-like material. 2. NO synthase from BRP used L-arginine as a substrate, required NADPH, tetrahydrobiopterin, and FAD as co-factors and was Ca2+/calmodulin-dependent. The activity of NO synthase was inhibited by NG-methyl-L-arginine and NG-nitro-L-arginine, and haemoglobin blocked the effect of NO formed by the enzyme. 3. On reducing SDS polyacrylamide gel electrophoresis the apparent molecular mass of NO synthase from BRP was 160 +/- 2 kDa, which is similar to that of the cerebellar NO synthase. Protein immunoblot and immunoprecipitation showed that NO synthase from BRP cross-reacted with the selective antiserum to neuronal NO synthase from rat cerebellum. 4. Immunohistochemistry using the same antiserum demonstrated that NO synthase in BRP was located exclusively within nerve fibres. Thus, autonomic nerves synthesizing the NANC neurotransmitter seem to contain an isoform of NO synthase which is similar to that from rat cerebellum.

Inhibition of nicotine-induced relaxation of the bovine retractor penis muscle by β-adrenoceptor antagonists

The relative potency in inhibiting nicotine-induced relaxation of the bovine retractor penis muscle (BRP) was estimated for the racemates of seven β-adrenoceptor antagonists, both of the optical isomers of propranolol, and lidocaine. The order of potency of the drugs studied was (+)-propranolol>(−)- propranolol>propranolol>alprenolol>metoprolol>lidocaine>acebutolol>pindolol >sotalol>atenolol. It is concluded that the inhibition of the relaxation was not due to blockade of β-adrenoceptors but to the nonspecific effects of the β-adrenoceptor antagonists. It is also concluded that the neurotransmitter(s) which was (were) released from the non-adrenergic non-cholinergic inhibitory nerves in the BRP did not relax the muscle by activating the β-adrenoceptors. It is suggested that the β-adrenoceptor antagonists inhibited the release of the inhibitory neurotransmitter(s) by a mechanism which is significantly correlated to their lipophilicity.

Effects of NG‐substituted analogues of l‐arginine on NANC relaxation of the rat anococcygeus and bovine retractor penis muscles and the bovine penile artery

1. The effects of two inhibitors of nitric oxide synthase, NG-monomethyl L-arginine (L-NMMA) and NG-nitro L-arginine (L-NOARG), were examined on non-adrenergic non-cholinergic (NANC) inhibitory transmission in the rat anococcygeus, bovine retractor penis (BRP) and bovine penile artery. 2. In the rat anococcygeus, L-NMMA (10-1000 microM) produced a concentration-dependent augmentation of guanethidine (30 microM)-induced tone and inhibited NANC relaxation at all frequencies tested (0.1-20 Hz): the maximum inhibition obtained was 56 +/- 6% (n = 6). L-NOARG (0.3-30 microM) also augmented tone and inhibited NANC relaxation in a concentration-dependent manner, but unlike L-NMMA the maximum inhibition was 100%. 3. In the BRP, L-NMMA (10-100 microM) had no effect on tone or NANC-induced relaxation, but at 1000 microM tone was increased and NANC relaxation inhibited by 25 +/- 7% (n = 6). L-NOARG (0.3-30 microM) produced a concentration-dependent increase in tone and inhibition of NANC relaxation. As in the rat anococcygeus, inhibition of NANC relaxation was complete. 4. The effects of L-NMMA and L-NOARG were stereospecific since D-NMMA (10-1000 microM) and D-NOARG (1-1000 microM) had no effect on tone or NANC relaxation of the rat anococcygeus or BRP. 5. L-Arginine (10-300 microM) had no effect by itself on NANC-induced relaxation of the rat anococcygeus or BRP. It did, however, reverse the ability of L-NMMA (10-1000 microM) to augment tone and inhibit NANC relaxation in the rat anococcygeus and BRP. 6. On the bovine penile artery, both L-NMMA (100 microM) and L-NOARG (30 microM) augmented the tone induced by guanethidine (30 microM) and 5-hydroxytryptamine (0.2 microM) in an endothelium-dependent manner. L-NMMA had no effect on NANC-induced relaxation, but inhibited acetylcholine-induced endotheliumdependent relaxation. L-NOARG abolished NANC relaxation at all frequencies tested and inhibited acetylcholine-induced relaxation. D-NOARG (30 microM) had no effect on NANC or acetylcholine-induced relaxation. 7. The ability of L-NOARG to abolish NANC-induced relaxation in the rat anococcygeus, BRP and bovine penile artery suggests that the L-arginine-nitric oxide pathway mediates neurotransmission in all three tissues. The effectiveness of L-NMMA in blocking NANC relaxation-in the rat anococcygeus but not the BRP and bovine penile artery suggests a species difference in the neuronal nitric oxide synthase. The neuronal and endothelial nitric oxide synthases in the penile artery also appear to differ.

Inhibition of nicotine‐induced relaxation of the bovine retractor penis muscle by compounds known to have ganglion‐blocking properties

1. The relative potency in blocking the nicotine-induced relaxation of the bovine retractor penis muscle (BRP) was estimated for 12 drugs known to have ganglion-blocking properties. 2. The order of potency of the drugs studied was mecamylamine greater than chlorisondamine greater than pentolinium greater than propantheline greater than (+)-tubocurarine greater than hexamethonium greater than emepronium greater than tetraethylammonium greater than glycopyrrolate greater than decamethonium greater than butylscopolamine greater than scopolamine. 3. The results conform well to those obtained with other pharmacological methods used for the estimation of ganglion-blocking activity. 4. It is concluded that blockade of the nicotinic relaxation of the BRP can be used as an alternative method for quantitative assessment of ganglion-blocking activity. 5. Advantages of this technique are that it discriminates well between antinicotinic and antimuscarinic activity and that it satisfies most or all ethical and economical demands. 6. It is also possible that this method has certain value in predicting whether a drug has enough ganglion-blocking activity to be likely to cause impotence.

The effects of pyrogallol and hydroquinone on the response to NANC nerve stimulation in the rat anococcygeus and the bovine retractor penis muscles

1. The effects of pyrogallol and hydroquinone on the bovine retractor penis (BRP) and rat anococcygeus muscles to non-adrenergic, non-cholinergic (NANC) nerve stimulation have been examined. Both drugs at a concentration of 10(-4) M significantly reduced the response in the rat anococcygeus muscle but had no effect in the BRP muscle. 2. The inhibition of the NANC response in the rat anococcygeus muscle by pyrogallol was completely reversed by superoxide dismutase suggesting it was due to the generation of superoxide anions. 3. Pyrogallol inhibited the response to nitric oxide (NO) in the rat anococcygeus muscle but not that to 3-isobutyl-1-methyl-xanthine (IBMX) which confirmed a selective action. 4. These results suggest that the NANC neurotransmitter in the rat anococcygeus muscle is susceptible to superoxide anions and may be NO or a substance that can liberate NO.

Mechanism for the generation of active smooth muscle inhibitory factor (IF) from bovine retractor penis muscle (BRP)

The active smooth muscle inhibitory factor (IF) is generated by acidifying the extracts from the bovine retractor penis muscle (BRP). The activated IF is very similar to endothelium-derived relaxing factor (EDRF). However, the mechanism for the generation of active IF is yet unknown. From reverse-phase high performance liquid chromatographic data, the activities of nitrite loss were closely related to the contents of both sulfhydryl (SH) groups and L-cysteine. Thus, under acidic conditions, RSH and nitrite in the extracts are considered to react as follows: RSH + HNO 2 → RSNO + H 2O, RSNO → ( 1 2 ) RSSR + NO , NO + ( 1 2 ) O 2 → NO 2 , NO 2 + ( 1 2 ) H 2 O → ( 1 2 ) HNO 2 + ( 1 2 ) HNO 3 . In addition to NO, RSNO is also a labile but potent vasodilator. Thus, activated IF seems to consist of RSNO and NO, and thiol-containing small molecules (molecular weight of less than 1,000) from BRP are closely involved in the generation of active IF.