Effect of cholecystokinin on food intake at different stages of the estrous cycle in female rats.

Effects of cholecystokinin octapeptide (CCK-8) on feeding behavior were examined in male and female rats. After an 18-hour fast, ad lib food intake for 30 minutes was measured for each rat. In male rats, food intake measured for 30 minutes was significantly decreased by intraperitoneal injection of 0.25 to 1 microgram/kg of CCK-8 in a dose-dependent manner. The satiety effect of CCK-8 was blocked by L-364,718 (20 nmol/kg), a specific cholecystokinin receptor antagonist. In female rats, food intake at proestrus and estrus was significantly less than that at diestrus. Food intake of female rats at diestrus and metestrus was significantly decreased by an intraperitoneal injection of CCK-8 prior to feeding, but it was not affected at proestrus and estrus. The effect of CCK-8 on food intake at diestrus and metestrus was dose dependent and was nearly abolished when 20 nmol/kg of L-364,718 was administered simultaneously. The results of this study suggest that stages of the estrous cycle affect feeding behavior of rats. Further, cholecystokinin's regulatory action on feeding behavior appears to be effective at diestrus and metestrus, but not at proestrus and estrus.