Central oxytocin increases food intake and daily weight gain in rats

The present study was performed to investigate the effects of centrally administered oxytocin on weight gain and food intake in rats. Two substrains of Sprague-Dawley rats (A and B) differing in average daily weight gain were used. Female rats of substrain A gained 2 g per day and 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 injections of 1, 5, or 10 μg of oxytocin or isotonic saline in a volume of 5 μl were given. In females, ICV treatment with either saline or 5 μg of oxytocin caused a transient loss of weight within 24 h of treatment. However, in the more slowly growing females of substrain A depression in body weight was observed after a single treatment with saline, whereas the body weight of oxytocin-treated females showed less marked depression and rapidly returned to the pretreatment weight. After a 3-day treatment period an even greater difference in daily weight gain was seen between oxytocin-treated and saline-treated female rats of 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 substrain B. Intraperitoneal injections of 5 μg of oxytocin did not influence food intake or daily weight gain in female rats of substrain A. These data suggest that oxytocin may act centrally to influence food intake and daily weight gain in slowly growing female Sprague-Dawley rats.