Effects of estradiol-17β on basal and luteinizing hormone releasing hormone-induced secretion of luteinizing hormone and follicle stimulating hormone by ovine pituitary cell culture

Abstract

Ovine pituitary cells collected during anestrous season were cultured to study the effect of estradiol-17β (E2) on basal and luteinizing hormone releasing hormone (LHRH)-induced secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH). When pituitary cells were incubated with 1x10-9 M E2 for 6 h or longer, decreased FSH but increased LH basal secretion was observed. Further, both LHRH-induced FSH and LH release were enhanced by E2. The degree of this enhancement was dependent on E2 concentration, and a concentration of E2 higher than 10-11 M was required. There was a lag period of only 2 h before the agumentative effect of E2 on LHRH-induced FSH and LH release could first be measured. Our study also demonstrated that E2 not only reduced the LHRH concentration required for inducing the half-maximal response (ED50) of FSH and LH secretion, but it increased the maximal response of FSH and LH to LHRH stimulation. In addition, LHRH alone, or together with E2, altered intracellular and media concentration of gonadotropins, but not the total amounts. In conclusion, although E2 has different effects on the basal secretion of FSH and LH, it increases the responsiveness of ovine pituitary cells to LHRH-induced FSH and LH secretion. The sensitization effect of E2 is most likely exerted on the releasable gonadotropin pool rather than on de novo synthesis of FSH and LH.