Biology of Reproduction, Vol 23, 124-134, Copyright © 1980 by Society for the Study of Reproduction

Effects of Estradiol-17 on Basal and Luteinizing Hormone Releasing Hormone-Induced Secretion of Luteinizing Hormone and Follicle Stimulating Hormone by Ovine Pituitary Cell Culture

¹ Department of Biochemistry, North Carolina State University, Raleigh, North Carolina 27650

Ovine pituitary cells collected during anestrous season were cultured to study the effect of estradiol-17 (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 1 x 10^-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.

Note:
ACKNOWLEDGMENTS The kind gift of purified ovine FSH from Dr. H. J. Grimek is gratefully appreciated. The authors are also grateful to Miss Jackie Huff for performing the E₂ radioimmunoassay in Dr. Jack Britt’s laboratory, Department of Animal Science, North Carolina State University, Raleigh.

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