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The Interaction between ß-Endorphin and Gonadal Steroids in Regulation of Luteinizing Hormone (LH) Secretion and Sex Steroid Regulation of LH and Proopiomelanocortin Peptide Secretion by Individual Pituitary Cells¹

Department of Diabetes, Endocrinology, and Metabolism, City of Hope National Medical Center, Duarte, California 91010; and the Department of Medicine, Harbor-University of California-Los Angeles Medical Center, Torrance, California 90509

Address all correspondence and requests for reprints to: Fouad R. Kandeel, M.D., Ph.D., Department of Diabetes, Endocrinology, and Metabolism, City of Hope National Medical Center, 1500 East Duarte Road, Duarte, California 91010.

Reported studies using the conventional pituitary cell culture technique suggest that ß-endorphin (B-EP) produced locally in the pituitary or reaching it from the hypothalamus acts in conjunction with estradiol (E₂) to initiate and in conjunction with progesterone (P₄) to terminate the midcycle surge of LH. In addition, the reverse hemolytic plaque assay (RHPA) was used to investigate the effects of E₂ and P₄ on the secretory activity of individual pituitary cells. The results of these experiments indicate that 1) E₂ enhances the secretion of LH, ACTH, and B-EP by individual pituitary cells; 2) E₂ increases the number of secreting cells for each of the three hormones; 3) the rise in B-EP and ACTH secretion antecede that of LH; 4) P₄ augments ACTH and B-EP secretion by individual pituitary cells; and 5) P₄ has dual effects, acutely (1 h) potentiating LH secretion from already active cells and subsequently (8 h) recruiting cells that formerly had little or no secretory activities.

Collectively, the above studies support a role for steroid hormones in regulation of midcycle LH secretion at the pituitary level. The results also suggest that intrapituitary (paracrine/autocrine) and extrapituitary (endocrine) B-EP modulates gonadal steroid effects on LH secretion by pituitary gonadotrophs.

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