Park D, Cheon M, Kim C, Kim K, Ryu K. Progesterone together with estradiol promotes luteinizing hormoneβ-subunit mRNA stability in rat pituitary cells in vitro. Eur J Endocrinol 1996;134:236–42. ISSN 0804–4643 The present study examined the role of ovarian steroids, estradiol and/or progesterone in the regulation of luteinizing hormone β-subunit (LH-β) mRNA levels and LH release in the rat anterior pituitary cells cultured in vitro. When estradiol (10 nmol/l and/or progesterone (100 nmol/l) were added to the cultures, neither estradiol or progesterone nor both together altered the basal LH-β mRNA levels or LH release. Continuous exposure to gonadotropin-releasing hormone (GnRH, 0.2 nmol/l) for 24 h markedly induced LH-β mRNA accumulation, and in this experimental condition, progesterone alone and progesterone + estradiol further augmented GnRH-induced LH-β mRNA levels and LH release. Then we explored further the possibility that ovarian steroids are involved in modulating LH-β mRNA stability in cultured rat pituitary cells where transcription was inhibited by actinomycin D. Anterior pituitary cells were preincubated with GnRH (0.2 nmol/l) for 16 h and, after removing GnRH from culture medium, the cells were incubated further in the presence of actinomycin D (5 μmol/l) for 24 h. The LH-β mRNA levels gradually declined to about 30% of the control values (zero time point after GnRH removal) in a time-dependent manner. During this period, either progesterone alone or progesterone + estradiol clearly blocked the degradation of LH-β mRNA species. These results indicate that ovarian steroids promote LH-β mRNA stability, thereby contributing to the maintenance of GnRH-stimulated LH-β mRNA levels. Kyungza Ryu, Department of Pharmacology, College of Medicine, Yonsei University, 120-749, Seoul, Korea
