Bovine inhibin immediately inhibits the electrophysiological response to chorionic gonadotrophin in ovarian follicles of Xenopus laevis.
Inhibin was originally isolated from ovarian tissue using, as a bioassay, its ability to diminish synthesis and secretion of gonadotrophins in pituitary cells after several days. Inhibin is known also to modify responses to gonadotrophins in the ovary after stimulation times of hours or days. Here we show that action for less than 4 min of purified bovine inhibin on ovarian follicles from Xenopus laevis causes a specific, dose-responsive (greater than 10 U/ml) inhibition of the membrane hyperpolarization produced by stimulation with chorionic gonadotrophin. The CG-induced change in follicle membrane potential has previously been shown to be caused by potassium efflux produced by rises in intracellular cAMP. Inhibin did not affect similar hyperpolarization stimulated by 10 microM adenosine. The apparent Ca(2+)-dependent Cl- currents which are often associated with CG action, were not inhibited by inhibin. At concentrations up to 2000 U/ml, inhibin did not significantly alter the timing of CG-induced germinal vesicle breakdown in the oocytes, which may suggest functional action on other developmental processes.
Murray-McIntosh
R P
RP
Department of Obstetrics and Gynaecology, Wellington School of Medicine, University of Otago, New Zealand.
Vos
M
M
Lacy
M P
MP
D000818:Animals; D002417:Cattle; D002470:Cell Survival / Q000187:drug effects; D006063:Chorionic Gonadotropin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D007265:Inhibins / Q000494:pharmacology*; D009865:Oocytes / Q000502:physiology; D010053:Ovary / Q000187:drug effects* / Q000502:physiology; D014982:Xenopus laevis
D006063:Chorionic Gonadotropin; D007265:Inhibins