PITUITARY-GONADAL INTERACTIONS IN PERINATAL RATS - RELATIONSHIPS OF PLASMA LUTEINIZING-HORMONE AND TESTOSTERONE CONCENTRATIONS, AND PITUITARY LEVELS OF LH SUBUNIT MESSENGER-RNAS
P. Pakarinen et al., PITUITARY-GONADAL INTERACTIONS IN PERINATAL RATS - RELATIONSHIPS OF PLASMA LUTEINIZING-HORMONE AND TESTOSTERONE CONCENTRATIONS, AND PITUITARY LEVELS OF LH SUBUNIT MESSENGER-RNAS, Neuroendocrinology, 60(1), 1994, pp. 42-49
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.