RESUMEN
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.
Asunto(s)
Endotelinas/metabolismo , Músculo Liso/metabolismo , Pene/metabolismo , Fragmentos de Péptidos/metabolismo , Receptores de Endotelina/metabolismo , Animales , Arterias/efectos de los fármacos , Arterias/inervación , Arterias/metabolismo , Autorradiografía , Bovinos , Endotelina-3/farmacología , Endotelinas/farmacología , Procesamiento de Imagen Asistido por Computador , Radioisótopos de Yodo , Masculino , Relajación Muscular/efectos de los fármacos , Músculo Liso/efectos de los fármacos , Músculo Liso/inervación , Oligopéptidos/farmacología , Pene/irrigación sanguínea , Pene/efectos de los fármacos , Pene/inervación , Fragmentos de Péptidos/farmacología , Piperidinas/farmacología , Receptor de Endotelina B , Venenos de Víboras/farmacologíaRESUMEN
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.
Asunto(s)
Antagonistas de los Receptores de Endotelina , Endotelina-1/farmacología , Músculo Liso/efectos de los fármacos , Pene/efectos de los fármacos , Vasoconstrictores/toxicidad , Venenos de Víboras/toxicidad , Análisis de Varianza , Animales , Bovinos , Relación Dosis-Respuesta a Droga , Endotelinas/farmacología , Activación Enzimática/efectos de los fármacos , Dosificación Letal Mediana , Masculino , Relajación Muscular/efectos de los fármacos , Músculo Liso/metabolismo , Óxido Nítrico Sintasa/metabolismo , Pene/irrigación sanguínea , Fragmentos de Péptidos/farmacología , Péptidos Cíclicos/farmacologíaRESUMEN
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 NG-nitro-L-arginine, 3.2 x 10(-6) M tetrodotoxin, 5.0 x 10(-4) M hexamethonium, 5.3 x 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 x 10(-3) M 4-aminopyridine, 2.6 x 10(-2) M tetraethylammonium and 7.3 x 10(-4) M Ba2+. Exposure to K(+)-free solution reversibly abolished the neurogenic relaxations. The relaxations caused by 5.0 x 10(-7) M cromakalim and 2.0 x 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 x 10(-5) to 3.0 x 10(-3) M and tetraethylammonium 10(-4) to 2.6 x 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Relajación Muscular/efectos de los fármacos , Pene/efectos de los fármacos , Potasio/farmacología , Acetilcolina/farmacología , Animales , Bovinos , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Estimulación Eléctrica , Técnicas In Vitro , Masculino , Músculo Liso , Nicotina/farmacología , Ouabaína/farmacología , Vasodilatadores/farmacologíaRESUMEN
Inhibition of relaxation of strips of the bovine retractor penis muscle induced by a standard dose of nicotine (30 microM) 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.