INHIBITION OF GONADOTROPHIN SECRETION BY INDUCED HYPERPROLACTINAEMIA IN THE MALE RAT

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Abstract
Pituitary glands were transplanted under the kidney capsule to induce hyperprolactinaemia in both immature (41 days old) and adult (150 days old) intact male rats. Blood samples were taken for hormone analysis at regular intervals after transplantation and the animals were killed 42–45 days after the operation. Serum levels of prolactin rose in all groups of rats with transplants except in those animals bearing only one pituitary gland. Increased adrenal weight in all transplanted groups suggested that effective hyperprolactinaemia was always achieved. Serum levels of LH and FSH were significantly suppressed in all animals with transplants; the pituitary LH content was as reduced in all animals except those bearing one pituitary transplant but reductions in the pituitary FSH content were inconsistent. Although the amount of luteinizing hormone releasing hormone (LH-RH) in the hypothalamus did not differ significantly between groups, the effects of hyperprolactinaemia on serum and pituitary levels of LH and FSH suggested a functional lack of LH-RH (possibly due to an increase in the sensitivity of the hypothalamus to the negative feedback effects of testicular steroids). Serum levels of testosterone remained normal in spite of reductions in the serum concentrations of LH and FSH and, in immature animals, a reduction in testicular binding of LH/human chorionic gonadotrophin. These results are discussed in the light of previous conflicting reports on the effects of induced hyperprolactinaemia on the regulation of secretion of LH and FSH.