Characterization of nerve-induced relaxation of gastrointestinal sphincteric smooth muscle in a South American opossum (Didelphis albiventris)

The presence of inhibitory nonadrenergic noncholinergic (NANC) intrinsic innervation of the circular muscle of the gastrointestinal sphincters of the South American (SA) opossum was investigated in vitro. Isolated circular muscle strips from the esophagogastric and ileocolonic junctions but not from the gastroduodenal (pylorus) region developed spontaneous tension. Tetrodotoxin (TTX, 1 muM) augmented the spontaneous tension only in the ileocolonic junction strips. Electrical field stimulation of esophagogastric and ileocolonic junction strips caused frequency-dependent responses consisting of a relaxation at lower frequencies (<1 Hz) and a biphasic response or contraction at higher frequencies. In the strips from the pyloric region electrical field stimulation abolished the spontaneous activity at lower frequencies and induced contractions at higher frequencies. The responses elicited by electrical field stimulation in the three sphincters were abolished by TTX (1 muM). Electrical field-induced contractions were reduced while relaxations were enhanced by atropine (1 muM). In the presence of atropine (1 muM) and guanethidine (3 muM), electrical field stimulation, nicotine and ATP induced frequency-or concentration-dependent relaxations of the three sphincters that were abolished by TTX (1 muM). Isoproterenol and sodium nitroprusside caused concentration-dependent relaxations which were TTX-resistant. These findings indicate that the sphincteric circular muscle of the SA opossum gastrointestinal tract is relaxed by the activation of intrinsic NANC nerves and therefore can be used as a model for the study of the mechanisms involved in these responses.

Bloqueio regional intra-venoso com guanetidina / Regional intravenous block with guanetidin

Demonstra-se a utilidade prática do bloqueio regional intra-venoso com Guanetidina em oito pacientes com dor; salienta-se a simplicidade de execuçäo, segurança, maior conforto e menor invasividade

Ovulatory response to the sequential administtration of follicle stimulating hormone and human chorionic gonadotropin by autografted ovary in unilaterally ovariectomized adult rat with peripheral devervation induced by guanethidine treatment

Ratas hembras adultas con cilos estrales regulares de 4 días de duración fueron unilateralmente ovariectomizadas (se extirpó el ovario derecho) en el día del diestro 1; en el mismo acto, el ovario fue injertado en el tejido celular subcutáneo. Um grupo de estos animales fue inyectado con guanetidina (20 mg/Kg) cada 72 horas, durante 30 días. Todos los animales (tratados o no con guanetidina) fueron autopsiados, en el primer día de estro vaginal luego del período de 30 días. En otro experimento, ratas hemicastradas con auntoinjerto de ovario, tratadas o no con guanetidina como en el experimento anterior, a los 30 días luego de la hemiovariectomia y el autoinjerto, estando en diestro, fueron tratadas con 45 i.u de hormona folículo estimulante ovina (FSH); 56 horas después recibieron 25 u. i. de gonadotropina coriónica humana (hCG) y fueron autopsiadas 20 horas después. Otro grupo de animales con hemicastración y autoinjerto, con o sin tratamiento con guanetidina, en el día treinta del postoperatório, también en diestro, fueron inyectados con 10 ng de benzoato de benzoato de estradiol (BE) y se les autopsió en el primer día de cornificación vaginal que siguió al tratamiento. La tasa de animales ovulantes en el ovario in situ no fue modificada por el tratamiento con guanetidina, FSH y hCG o BE. La administración de guanetidina provocó disminución del número de ovocitos liberados por animal ovulante (8.3 ñ 0.8 vs 10.4 ñ 0.3, - < 0.05) y menor peso final del ovario remanente que en el grupo no tratado (18.8 ñ 0.7 vs 23.7 ñ 0.7, - < 0.01). Aunque el grado de hipertrofia compensadora fue similar en ambos grupos (45.5% y 48.8%). La respuesta ovulatoria (tasa de animales ovulantes y número de ovocitos liberados por animal ovulante) y el aumento del peso del ovario remanente inducidos por la administración de FSH y hCG o de BE, no fueron modificados por el tratamiento previo con guanetidina. El estudio histológico del injerto de ovario realizado en los animales sin tratamiento, o que fueron inyectados con guanetidina, FSH y hCG o benzoato de estradiol, no mostró signos de ovulación...

Influence of reserpine and guanethidine on the responses of the isolated rat ileum to catecholamines.

The sensitivity of the isolated ileum of the rat to catecholamines has been investigated using normal, reserpinized and guanethidine treated animals. Both reserpine and guanethidine treatment produces supersensitivity to adrenaline, noradrenaline and to a greater extent to isoprenaline.

Cardiac acceleration by angiotensin II in dogs.

The effect of angiotensin II on heart rate of dogs were studied by intravenous and intracerebroventricular routes. Following differences were noticeable when the results obtained with intracerebroventricular were compared with those obtained after intravenous administration. The onset of tachycardia was less as compared to the intravenously administered angiotensin. The dogs required to produce tachycardia was less and the magnitude of tachycardia was also greater with intracerebroventricular administration. The initial bradycardia observed with intracerebroventricular or intravenous administration of angiotensin, could be prevented by using the mechanical buffering device. The spinal cord transection at C2 level and bilateral vagotomy abolished the tachycardia. It is speculated that angiotensin acts centrally either on the hypothalamic or medullary accelerator neurones (central sympathetic structures) and produces some degree of increased adrenegic neuron discharge which is responsible for cardiac acceleratin in dogs.