PITUITARY-GONADAL INTERACTIONS IN PERINATAL RATS - RELATIONSHIPS OF PLASMA LUTEINIZING-HORMONE AND TESTOSTERONE CONCENTRATIONS, AND PITUITARY LEVELS OF LH SUBUNIT MESSENGER-RNAS

The functional state of the pituitary-gonadal axis was studied in rats on days 18.5-21.5 of fetal life (f) and on day 4 postpartum by measur ements of plasma levels of luteinizing hormone (LH) and testosterone ( T). LH was measured using an ultrasensitive immunofluorometric assay. In addition, male fetuses were castrated and exposed to the antiandrog en flutamide (FL; 100 mg/kg BW) or the Leydig cell-specific cytotoxic agent ethylene dimethane sulphonate (EDS, 50 mg/kg BW on 2 days) by in jections of the drugs to the mothers. Besides LH and T, pituitary leve ls of LH subunit mRNAs were measured in these animals. The results all owed the following conclusions: (1) the plasma LH levels in both sexes are low (<0.05 mu g/l, NIH rLH RP-2) on days f18.5 and f19.5; (2) a 4 - to 5-fold increase in plasma LH occurs between days f19.5 and f20.5, and a 3- to 4-fold sex difference appears (females > males); (3) the activation of fetal testicular T production before day f19.5 takes pla ce in the face of very low plasma LH (<0.02 mu g/l), suggesting that s ome factor(s) other than LH may stimulate the testis at this age; (4) the reciprocal changes of plasma LH and T, and the experiments with ca stration, EDS and FL demonstrate that testicular feedback regulation o f LH secretion is functional from day f19.5 onwards; (5) the parallel changes of T in male and female fetal plasma suggest that T in female fetuses comes from male littermates, and (6) the fetal pituitary-testi cular axis is less sensitive to hormonal manipulations than that of th e postnatal animal, possibly due to interference of maternal and place ntal hormones with the pituitary-testicular interactions.