Pancreatic glucagon and postprandial satiety in the rat

The hypothesis that administration of pancreatic glucagon inhibits feeding by eliciting satiety for food was tested against several behavioral and physiological criteria of specificity. The effects of intraperitoneal glucagon injections on intake of a palatable milk diet were tested in rats maintained with ad lib access to pelleted diet. Injections of 25--800 micrograms/kg glucagon administered at meal onset inhibited meal size by 17--36%, but did not affect the normal postprandial behavioral satiety sequence or elicit any behavioral signs of toxicity. Latency to rest and intermeal interval were not affected. Glucagon decreased meal size by specifically inhibiting feeding during the terminal phase of the meal without affecting feeding earlier in the meal. This was also the case when glucagon was injected 4 min prior to meal onset. This range of glucagon doses did not affect water intake in water deprived rats consuming fluid volumes comparable to the milk intakes. They also did not affect body temperature. Finally, injection of 400 micrograms/kg glucagon after the initial exposure to a novel drinking fluid was not sufficient to form a conditioned taste aversion in a two bottle preference test. These data, together with reports that circulating pancreatic glucagon levels increase during meals, strongly suggest that pancreatic glucagon is involved in the production of postprandial satiety.