Involvement of prolactin in the onset of puberty in female rats.

Abstract

Pimozide (1 mg/kg per day), bromocriptine (1 mg/kg per day) or domperidone (0.1 mg/kg per day) administered daily to rats from day 21 did not change the age at which vaginal opening occurred, nor did they affect the body weight at that age. Therefore the evolution of prolactin levels was different in these three groups. The pimozide-treated group showed high prolactin levels measured on day 23, at vaginal opening and at first oestrus. In the bromocriptine-treated group, levels were undetectable on the day of vaginal opening. Chronic treatment with domperidone failed to increase prolactin levels on day 23 and at vaginal opening. Nevertheless, large increases were observed after a single injection of domperidone at both 21 and 30 days of age. A significant increase in LH observed on day 23 in the pimozide-treated group was the only effect on gonadotrophin levels which was detected. Ovarian weights were unaffected by the treatments, whereas adrenal weight was increased in the bromocriptine-treated group and decreased in the pimozide- and domperidone-treated groups. Female rats grafted on day 21 with one additional pituitary gland from adult (90 days) or young (21 days) donors showed a similar advancement in the time of vaginal opening, although the animals bearing an adult pituitary gland showed higher prolactin levels than those observed in animals grafted with young pituitary glands. This study suggested that the onset of puberty is not closely linked with the evolution of prolactin levels and that the hormone itself is not indispensible for the process.