Comparison between K+-induced and LHRH-induced gonadotropin secretion in vitro.
The effect of elevated external [K+] compared to luteinizing hormone-releasing hormone (LHRH) on gonadotropin secretion was studied in vitro in superfused pituitary fragments from cyclic female rats. Challenging proestrous but not estrous pituitaries with a 2-h pulse of 0.8 nM LHRH produces two distinct peaks in the curve for the first derivative of gonadotropin secretion versus time; the second peak exceeds the initial one and represents expression of LHRH self-priming. Challenging proestrous pituitaries with a 2-h pulse of raised [K+] results in an initial increase in secretion followed by a positive slope of the secretion rate curve for LH but a constant rate for follicle-stimulating hormone (FSH); the positive slope is blocked by cycloheximide and not found with estrous pituitaries pulsed with raised [K+]. Proestrous pituitaries exhibit a graded response to 10-min pulses of raised external [K+] from 10-91 mM for LH and 10-47 mM for FSH secretion. LHRH followed by elevated [K+] primed the LH and FSH response to the secretagogue, but the reverse sequence did not. The results show 1) a concentration dependence of elevated [K+]-induced LH and FSH secretion, 2) a LHRH specific initiation of priming that does not require the immediate presence of LHRH for its subsequent expression, and 3) a gonadotropin secretory response to elevated [K+] that varies during the estrous cycle and can be modified by protein synthesis inhibition or progesterone administration.
D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D011247:Pregnancy; D011359:Proestrus; D051381:Rats; D011919:Rats, Inbred Strains
D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D011188:Potassium