Possible Role of Prolactin in the Inhibitory Effect of Estradiol on the Hypothalamic-Pituitary-Testicular Axis in the Rat*

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Abstract
Acute estradiol benzoate (EB) administration to intact adult male rats reduced basal and hCG-stimulated plasma testosterone (T) levels and decreased basal and LHRH-stimulated LH levels. Long term EB administration had similar effects on T levels. Basal LH levels were more markedly depressed than during short term administration, but the response to LHRH stimulation was increased. PRL levels were significantly elevated during both short and long term EB treatment. Hyperprolactinemia induced by grafting two pituitaries of littermate donors under the kidney capsule of a male adult intactrat was associated with reduced basal and LHRH-stimulated LH levels and reduced T responses to hCG. The administration of bromocriptine to EB-treated rats prevented the increase in serum PRL in response to estrogen and restored normal LH responses to LHRH and T responses to hCG. This suggests that PRL may play an intermediary role in the inhibitory effect of estrogens on pituitary-testicular function.