Regulation of LH subunit mRNA levels by gonadal hormones in female rats.

Abstract

To determine the physiological role of the ovaries in regulation of LH subunit gene expression, levels of cytoplasmic mRNA were measured in a cDNA-RNA dot-blot hybridization assay. An increase (twofold) in alpha mRNA was first detected 8 days after ovariectomy and then remained stable for 4 weeks. In contrast, LH-beta mRNA increased by 60-79% within 12 h of removing the ovaries and then rose progressively to six times the intact values at 3 and 4 weeks. Increases in LH-beta mRNA were always greater than those of alpha mRNA. Oestradiol, and oestradiol plus progesterone, but not progesterone alone, prevented the rise in alpha and LH-beta mRNA 10 days after ovariectomy. Three days after ovariectomy, alpha mRNA, but not LH-beta mRNA, was suppressed to below intact control values by oestradiol and oestradiol plus progesterone, indicating greater sensitivity of alpha mRNA to oestradiol inhibition at this stage. A single injection of oestradiol (1 microgram s.c.) to rats ovariectomized 14 days previously transiently suppressed alpha and LH-beta mRNA levels and serum LH concentrations in parallel for 1-8 h, after which high preinjection values were restored. However, pituitary LH content remained suppressed after LH mRNA levels had returned to the control values of ovariectomized rats. In most instances there was a qualitative positive correlation between changes in alpha and LH-beta mRNA, pituitary LH content and serum LH concentrations. LH content reflected LH-beta mRNA changes more closely than those of alpha mRNA. However, in oestradiol-treated rats ovariectomized 10 days previously, LH content remained increased despite normalization of the LH-beta and alpha mRNA levels, suggesting differential sensitivity to oestradiol of the gene expression and translational processes. Thus divergence of pre- and post-translational regulation of LH biosynthesis was demonstrated. These results imply an important physiological role for female sex hormones in the control of LH gene expression and LH biosynthesis. Prolactin mRNA fell by 30-50% for the first 2 weeks after ovariectomy, but by 3 and 4 weeks values were similar to those of intact controls. Serum and pituitary prolactin levels were reduced by 50% or more at all time-points, despite normalization of mRNA. Treatment of ovariectomized rats for 10 days with oestradiol and progesterone, either alone or combined, reversed the fall in prolactin mRNA and serum and pituitary prolactin levels. These changes in prolactin gene expression and synthesis were opposite to those of LH subunits in response to the same in-vivo hormone manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)