Many reports indicate that prolactin has a role in puberty occurrence. The present study was developed to evaluate the action of pituitary grafts on puberty. Female rats grafted on day 21 with ‘adult’ (90 days old) or ‘young’ (21 days old) pituitaries showed precocious vaginal opening and first estrus. The puberty advancement induced by ‘adult’ transplants was due to an increase in plasma prolactin values and can be blocked by bromocriptine treatment. The puberty advancement induced by ‘young’ transplants was not associated with increased prolactin levels and cannot be blocked by bromocriptine. These results suggest the existence of two possible mechanisms in precocious puberty induced by pituitary grafts: a prolactin-dependent one and another one not directly related with prolactin.

The present study analyzes the mechanism of precocious puberty induced in female rats after a ‘young’ pituitary graft (obtained from 21-day-old animals). For this purpose, the following experiments have been performed: (1) female rats were grafted or sham-operated on day 21 with a littermate’s pituitary the follicle-stimulating hormone (FSH), luteinizing hormone (LH) and estradiol plasma levels as well as the ovarian, uterine and adrenal weights were determined at different times after the graft; (2) female rats grafted or sham-operated on day 21 were treated with 0.2 ml of LH antiserum (LHAS) or the same volume of a normal horse serum (NHS); (3) female rats were injected on day 1 of life with 0.1 mg of estradiol benzoate or olive oil. Groups of these animals were decapitated daily between days 6 and 21 in order to measure gonadotropins and prolactin (PRL) pituitary content. Since on day 21 estrogenized females showed decreased gonadotropin content and normal PRL content, females in experiment 4 were grafted on day 21 with pituitaries obtained from control or neonatally estrogenized female rats. The results obtained showed that FSH, LH and estradiol plasma levels as well as ovarian and uterine weights increased after pituitary grafts. LHAS blocked the precocious puberty induced by the pituitary graft, and pituitaries obtained from neonatally estrogenized female rats were unable to modify the occurrence of puberty when grafted. In conclusion, this work evidences that precocious puberty induced by ‘young’ pituitary grafts was mediated by the increase in LH secretion from the graft.