Dependence of GnRH action on Na+, K+, and Ca2+ in the frog, Rana pipiens, pituitary.
The roles of K+, Ca2+, and Na+ ions in the mechanism of gonadotropin releasing hormone (GnRH) action on frog (Rana pipiens) hemipituitaries were studied using an in vitro superfusion system. The effects of elevated K+ alone or in combination with Ca2+-depleted medium, tetrodotoxin (TTX), or with 100 ng/ml GnRH were examined. The involvement of K+ was also studied indirectly through the use of tetraethyl ammonium chloride (TEA). The importance of Ca2+ was established by the loss of responsiveness to GnRH in Ca2+-depleted medium, or in the presence of the Ca2+ competitor CoCl2. The absence of a major dependence of GnRH on Na+ was revealed by the continued gonadotropin secretion after addition of 1 microM TTX to medium containing GnRH or 36.3 mM KCl, or by replacement of NaCL with choline chloride. High (10 X normal) KCl (36.3 mM) stimulated gonadotropin--both LH and FSH--secretion, but the response was more gradual than for GnRH. The inclusion of TEA (to block K+ efflux) in medium with GnRH accentuated the effect of GnRH, and the effects of elevated (36.3 mM) KCl and 100 ng/ml GnRH (a relatively high dose) were additive. Responses to high K+, like GnRH, were abolished by removal of Ca2+ from the medium. Overall, the roles of K+, Ca2+, and Na+ ions in the mechanism of GnRH action are very similar between mammals and frogs; Ca2+ apparently serves a critical function in the mechanism of GnRH action, while Na+ appears not to be involved. K+ can induce gonadotropin secretion, but it is not clear that it plays a direct role in the mediation of the action of GnRH.
D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology*; D003035:Cobalt / Q000494:pharmacology; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology*; D011894:Rana pipiens; D012965:Sodium Chloride / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D013757:Tetraethylammonium Compounds; D007987:Gonadotropin-Releasing Hormone; D003035:Cobalt; D013779:Tetrodotoxin; D012965:Sodium Chloride; D019789:Tetraethylammonium; D011189:Potassium Chloride; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; C018021:cobaltous chloride; D002122:Calcium Chloride