Diurnal variations of prolactin in the plasma of maturing female rats bearing hypothalamic lesions.

Previous evidence from our laboratory suggested a possible involvement of prolactin (PRL) in the induction of precocious puberty due to hypothalamic lesions in maturing female rats. In the present report the concentrations of PRL in plasma of lesioned and control rats were determined three times a day at three different periods of puberty. Lesions were produced in 20 day-old rats by a radiofrequency current in the anterior hypothalamic area (AHA). Intact littermates were used as control. Respectively 23, 25 and 28 day-old lesioned and control rats were bled at 08.00, 12.00 or 16.00 h. PRL levels, measured by RIA were determined from plasma aliquots. In control rats, elevated plasma PRL levels were found in the afternoon. Hypothalamic lesion induced a tendency to elevate tonically the PRL plasma concentrations which was evident at 16.00 h in 23 and 25 day-old rats and at 08.00 and 12.00 h in 28 day-old rats. The present results give additional support to our previous suggestion that PRL secretion is modified by the effect of lesions in the AHA.