CENTRAL OXYTOCIN INCREASES FOOD-INTAKE AND DAILY WEIGHT-GAIN IN RATS

The present study was performed to investigate the effects of centrall y administered oxytocin on weight gain and food intake in rats. Two su bstrains of Sprague-Dawley rats (A and B) differing in average daily w eight gain were used. Female rats of substrain A gained 2 g per day an d males gained 7 g. Female rats of substrain B gained 5 g per day and males gained 8 g. Animals were implanted with a stainless steel guide cannula, allowing ICV injections into the lateral ventricle. ICV injec tions of 1, 5, or 10 mu g of oxytocin or isotonic saline in a volume o f 5 mu l were given. In females, ICV treatment with either saline or 5 mu g Of oxytocin caused a transient loss of weight within 24 h of tre atment. However, in the more slowly growing females of substrain A dep ression in body weight was observed after a single treatment with sali ne, whereas the body weight of oxytocin-treated females showed less ma rked depression and rapidly returned to the pretreatment weight. After a 3-day treatment period an even greater difference in daily weight g ain was seen between oxytocin-treated and saline-treated female rats o f substrain A. In contrast, no difference in daily weight gain or food intake was observed between oxytocin- and saline-treated male rats of substrain A, nor in females or males of the more rapidly growing subs train B. Intraperitoneal injections of 5 mu g of oxytocin did not infl uence food intake or daily weight gain in female rats of substrain A. These data suggest that oxytocin may act centrally to influence food i ntake and daily weight gain in slowly growing female Sprague-Dawley ra ts.