SEXUALLY DIFFERENTIATED ROLE OF CALCIUM-IONS IN CHICKEN GNRH-I-STIMULATED RELEASE OF LH FROM ANTERIOR-PITUITARY GLANDS FROM ADULT DOMESTIC CHICKENS

Continuous perifusion of quartered anterior pituitary glands from juve nile and adult chickens of both sexes with chicken gonadotrophin-relea sing hormone-I (cGnRH-I) stimulated a spike-plateau profile of luteini zing hormone (LH) secretion. When perifused in Ca2+ free medium, pitui tary glands from juveniles of both sexes and from adult cockerels but not those from laying hens, released LH in response to cGnRH-I. This r elease occurred at the same time as the spike phase of the response se en in the presence of extracellular Ca2+ and was not accompanied by a plateau phase of secretion. The magnitude of the plateau but not the s pike phase of LH secretion from pituitary glands from adult males and females was reduced by the L-type Ca2+ channel blocker, nifedipine. Th is suggests that the mechanism of cGnRH-I-induced LH release from pitu itary glands from laying hens is independent of mobilization of intrac ellular Ca2+, and that entry of Ca2+ during the spike phase of LH secr etion occurs through non-L-type Ca2+ channels. Both non-L-type and L-t ype Ca2+ channels operate during the plateau phase of secretion in adu lts of both sexes. The duration of the spike phase of LH release from pituitary glands from adult cockerels was curtailed in the presence of nifedipine. The spike phase of LH release from the adult cockerel pit uitary therefore involves three modes of Ca2+ flux, comprising an intr acellular Ca2+-dependent component and extracellular components involv ing Ca2+ entry through L-type and non-L-type Ca2+ channels. The findin g that the extracellular Ca2+ independent component of cGnRH-I-stimula ted LH release from pituitary glands from juvenile hens is not present in adult hens suggests that this difference is related to sexual matu ration. The maturational and sexual differences in the LH response to cGnRH-I could be mediated through the high concentrations of plasma 17 beta-oestradiol in adult hens which suppress the mobilization of intr acellular stores of Ca2+ in the gonadotrophes. (C) 1995 Academic Press , Inc.