RESUMO
A systematic morphological and biochemical examination of the pituitary-testicular axis in the male restricted (Hre) rat was undertaken in order to understand the possible site(s) and mechanism(s) responsible for their infertility. The adult Hre rat had increased plasma levels of LH and FSH but normal levels of prolactin and testosterone, and normal weights of the sex accessory glands. The increased plasma levels of LH and FSH correlated with hypertrophy and vacuolation of the gonadotrophs in Hre rats. Leydig cells from adult Hre rats exhibited an enhanced testosterone response to LH and hCG in vitro but not in vivo. There was a shift in the normal age-related decline in the response of cultured Sertoli cells to FSH in Hre rats, which was evident as early as 25 days of age, and which corresponded to a delay of 10-14 days in the pubertal increase in testicular weight. The search for the mechanism of the suppression of spermatogenesis in the Hre rat should take into account two events, which may or may not be related: (i) the delay in the onset of spermatogenesis during puberty and (ii) inhibition of spermatogenesis in the adult, which may result from abnormal function of both the Sertoli and Leydig cells.