PROGESTERONE TOGETHER WITH ESTRADIOL PROMOTES LUTEINIZING-HORMONE BETA-SUBUNIT MESSENGER-RNA STABILITY IN RAT PITUITARY-CELLS CULTURED IN-VITRO

The present study examined the role of ovarian steroids, estradiol and /or progesterone in the regulation of luteinizing hormone beta-subunit (LH-beta) mRNA levels and LH release in the rat anterior pituitary ce lls cultured in vitro. When estradiol (10 nmol/l) and/or progesterone (100 nmol/l) were added to the cultures, neither estradiol or progeste rone nor both together altered the basal LH-beta mRNA levels or LH rel ease. Continuous exposure to gonadotropin-releasing hormone (GnRH, 0.2 nmol/l) for 24h markedly induced LH-beta mRNA accumulation, and in th is experimental condition, progesterone alone and progesterone + estra diol further augmented GnRH-induced LH-beta mRNA levels and LW release . Then we explored further the possibility that ovarian steroids are i nvolved in modulating LH-beta mRNA stability in cultured rat pituitary cells where transcription was inhibited by actinomycin D. Anterior pi tuitary cells were preincubated with GnRH (0.2 nmol/l) for 16 h and, a fter removing GnRH from culture medium, the cells were incubated furth er in the presence of actinomycin D (5 mu mol/l) for 24h. The LW-beta mRNA levels gradually declined to about 30% of the control values (zer o time point after GnRH removal) in a time-dependent manner, During th is period, either progesterone alone or progesterone + estradiol clear ly blocked the degradation of LH-beta mRNA species. These results indi cate that ovarian steroids promote LH-beta mRNA stability, thereby con tributing to the maintenance of GnRH-stimulated LH-beta mRNA levels.