Effects of ovarian steroids on spontaneous and nerve-induced electrical activity of the oviduct and its attached membranes in the rabbit.

Abstract

Spontaneous and nerve-induced electrical activity was recorded with suction electrodes in the circular muscle, longitudinal peritoneal muscle and mesotubarium superius (MTS) of the rabbit’s oviductal isthmus. The oviductal isthmus with its attached membranes and perivascular, adrenergic nerves was isolated and arranged for recording of spontaneous and neurogenic electrical activity with suction electrodes. Spontaneous activity was characterized in terms of frequency and duration of action potential discharge; neurogenic activity in terms of the latency of the evoked action potential discharge. Both frequency and duration of spontaneous activity in circular muscle increased significantly 48 and 72 h after treatment with human chorionic gonadotropin (hCG). This effect was mimicked by ovariectomy and exogenous progesterone and abolished by exogenous estradiol. Spontaneous activity of peritoneal muscle and MTS was irregular and not influenced by hCG or exogenous steroids. All 3 muscles responded to nerve stimulation, but response latency was significantly shorter in the circular muscle than in peritoneal muscle and MTS. Latency was significantly shortened after administration of hCG, ovariectomy and exogenous progesterone, but was unaffected by exogenous estradiol. Latency in peritoneal muscle and MTS was not altered after hCG or hormonal treatments. These findings suggest that the circular muscle of the isthmus is functionally independent of the longitudinal muscle and MTS. The effects of hCG and hormonal treatments on the response to nerve stimulation are not consistent with the idea that adrenergic neurogenic activity is a primary factor regulating the functional behavior of the isthmus. This behavior is probably influenced mainly by the spontaneous myogenic activity of the circular muscle which in vivo might be modulated by changes in neuronal activity that could not be detected in our in vitro experiments.