Effects of systemic and central prolactin injections on food intake, weight gain, and estrous cyclicity in female rats.

It has been suggested that prolactin may contribute to the hyperphagia of lactation. Studies examining the effects of the systemic administration of prolactin on food intake, however, have produced varying results. In species other than the rat, central prolactin administration has been found to increase food intake, but it is not known if central prolactin administration increases food intake in rats. In the current study the effects of peripheral and central prolactin administration on food intake, weight gain, and estrous cyclicity in female rats were compared. Prolactin was administered twice daily at 0800 and at 1900 h either subcutaneously at 3 mg/kg or 1 mg/kg b.wt. or by intracerebroventricular (ICV) infusion (2 micrograms/0.5 microliter) for 10 days to female rats. Control animals received similar injections of vehicle. Food intake, body weight, and vaginal smears were taken daily. Results showed that peripheral administration of prolactin increased food intake and weight gain and disrupted vaginal cyclicity. In contrast, ICV administration increased food intake to the same extent as did systemic prolactin administration but had no effect on weight gain or cyclicity. These data suggest that prolactin acts both peripherally and centrally to regulate energy balance in the female rat.