PROLACTIN STIMULATES THE EXPRESSION OF LUTEINIZING-HORMONE CHORIONIC-GONADOTROPIN RECEPTOR MESSENGER-RIBONUCLEIC-ACID IN THE RAT CORPUS-LUTEUM AND RESCUES EARLY-PREGNANCY FROM BROMOCRIPTIN-INDUCED ABORTION

Timed pseudopregnancy (psp) and pregnancy were induced in adult female rats by mating with infertile and fertile males, respectively. Corpora lutea (CL) and the residual parts of the ovaries were isolated and analyzed for luteinizing hormone/chorionic gonadotropin (LH/CG) receptor mRNA by Northern blot and solution hybridization analyses. Several LH/CG receptor mRNA transcripts were detected that could code for an intact functional receptor (6.8, 4.4, and 2.6 kb) as well as several smaller truncated transcripts. LH/CG receptor mRNA abundance in CL varied dramatically during both psp and pregnancy, with peak levels seen during the period of maximal progestational activity (Days 5-10 of psp and Days 7-14 of pregnancy). During the period of functional luteolysis, LH/CG receptor mRNA abundance decreased to low levels. The changes in LH/CG receptor expression could be explained by hormonal regulation. Bromocriptin treatment inhibited pituitary prolactin secretion. This treatment had a potent luteolytic effect by decreasing the levels of LH/CG receptor mRNA and plasma progesterone during early pregnancy, resulting in embryonal resorption in pregnant rats. Exogenous prolactin acted as a anti-luteolysin to reverse these effects by restoring LH/CG receptor mRNA abundance either by increasing gene expression or by stabilizing mRNA transcripts from degradation in young CL