Adrenalectomized and non-adrenalectomized male rats were studied to evaluate the interplay of PRL and the adrenal in the regulation of LH secretion during hyperprolactinemia. Hyperprolactinemia was induced by transplantation of pituitaries beneath the kidney capsule or by exogenous administration. Basal serum LH levels were significantly reduced (P < 0.5) in adult male rats (>90 days of age) bearing ectopic pituitaries. Pituitary LH release after 10 but not 20 ng LHRH, in the presence or absence of the adrenal, was blunted (P < 0.05) during hyperprolactinemia. Furthermore, chronic hyperprolactinemia slightly suppressed the rise in serum LH after gonadectomy, whereas LH secretion after 20 ng LHRH was markedly diminished in the castrated, hyperprolactinemic male rat, effects which were independent of the presence of the adrenal. Acute hyperprolactinemia (6 h) in the presence but not in the absence of the adrenal in the adult male rat significantly inhibited the LH response to 20 ng LHRH. In the youn postpubertal male rat (45–55 days of age), acute hyperprolactinemia (18 h) inhibited LH release in response to LHRH, an effect, however, mediated entirely via the adrenal. Unlike the adult male rat, acute hyperprolactinemia in the absence of the adrenal elevated basal serum LH levels and sensitized the pituitary to exogenous LHRH.
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