The present studies utilized a pharmacologic approach to evaluate the role of
corticosterone-preferring
mineralocorticoid receptors (type I or MR) versus classic
glucocorticoid receptors (type II or GR) in the regulation of basal pituitary
luteinizing hormone (LH) secretion in vivo in male rats. Animals bearing indwelling intracardiac venous
catheters received a subcutaneous (s.c.) injection of either vehicle, the MR antagonist,
RU 752 (0.5 or 5.0 mg/kg
body weight), or the GR antagonist,
RU 486 (0.5 or 5.0 mg/kg
body weight). Additional groups of rats were implanted with indwelling intracerebroventricular (i.c.v.) cannulas and intravenous
catheters for
drug administration and blood withdrawal, respectively, and injected i.c.v. with vehicle or graded doses (0.1, 1.0 or 10.0 micrograms/rat) of
RU 752 or
RU 486. The MR
RU 752 failed to alter plasma LH concentrations regardless of dose or route of administration. In contrast, the GR antagonist,
RU 486, elicited significant, dose-dependent increases in circulating LH when given either s.c. or i.c.v. Animals injected s.c. with either 0.5 or 5.0 mg
RU 486/kg
body weight showed elevated plasma LH levels; while the magnitude of this secretory response was not different between the two
drug-treated groups,
hormone levels remained elevated over baseline for a longer period of time in rats given the higher dose. Central administration of
RU 486 at a dose of either 1.0 or 10.0 micrograms also resulted in elevated LH release; both the magnitude and duration of this increase in plasma LH were dose-dependent. In additional experiments, groups of rats were pretreated with vehicle or the synthetic GR agonist,
RU 362, before administration of
RU 486.(ABSTRACT TRUNCATED AT 250 WORDS)