Dissociated changes of pituitary luteinizing hormone-releasing hormone (LHRH) receptors and responsiveness to the neurohormone induced by 17 beta-estradiol and LHRH in vivo in the rat.
A single injection of 17 beta-estradiol into castrated male or female rats results in an initial decrease in plasma concentrations of LH and pituitary responsiveness to LHRH, followed by a rapid return to normal or slightly elevated values. Under such experimental conditions, no acute change of binding of [125I-labeled D-Ser(TBU)6]LHRH ethylamide to anterior pituitary homogenate could be observed. Moreover, the self-priming effect of LHRH, as illustrated by a 10-fold increase in the LH response to a second injection of LHRH in the afternoon of proestrus, is accompanied by a 40% loss of pituitary LHRH receptors. During the estrous cycle, a 100% increase in pituitary LHRH receptors is already found on diestrus II, while the maximal LH responsiveness to LHRH occurs later, namely on the afternoon of proestrus. The present findings of a dissociation between changes in LHRH receptor levels and LH responsiveness to the neurohormone suggest that postreceptor events play a predominant role in the control of gonadotropin secretion by sex steroids and LHRH itself. Moreover, LHRH can cause an acute down-regulation of its own receptor in the anterior pituitary gland.
D000818:Animals; D002369:Castration; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011966:Receptors, LHRH
D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol