Regulation of LHRH Action and FSH Synthesis by Estradiol, Progesterone, and Inhibin

摘要

Progesterone modulation of pituitary function has been particularly difficult to define in the past. Progesterone responsiveness declines within 8 days in primary ovine pituitary cultures, and its action was completely overlooked for several years. By contrast, the activities of E and inhibin are maintained for 3 or 4 weeks in culture. Ovariectomy obliterates progesterone responsiveness at the pituitary level in vivo although P can still apparently act at the hypothalamus. Most studies to date have found minimal effects for P, but this may be due to problems associated with its correct analysis in vivo. The authors in vitro data predict that P plays a major negative role at the pituitary level on: (1) transcription of the genes encoding the alpha and FSH(beta) subunits, (2) LHRH binding and responsiveness, and (3) the length of poly(A) tails on alpha and LH(beta) mRNAs; it is reasonable to believe that FSH(beta) mRNA may be shortened also. The data also predicts that P plays a major role in preparing the pituitary for the preovulatory LH surge.