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 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-beta mRNA levels or LH release. Continuous exposure to gonadotropin-releasing hormone (GnRH, 0.2 nmol/l) for 24 h markedly induced LH-beta mRNA accumulation, and in this experimental condition, progesterone alone and progesterone + estradiol further augmented GnRH-induced LH-beta mRNA levels and LH release. Then we explored further the possibility that ovarian steroids are involved in modulating LH-beta 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 mumol/l) for 24 h. The LH-beta 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-beta mRNA species. These results indicate that ovarian steroids promote LH-beta mRNA stability, thereby contributing to the maintenance of GnRH-stimulated LH-beta mRNA levels.