Effect of Glucagon and of Insulin on Serum Free Fatty Acids in Normal and Depancreatized Dogs ∗

Summary and Conclusions

Intravenous injections of glucagon were followed by a triphasic response in serum FFA concentration: an immediate rise, probably reflecting the lipolytic effect of the hormone, a secondary depression probably caused by hypergly-cemia and by exogenous and/or endogenous insulin and a final rise which may have been the result of continued glucagon-induced lipolysis. It may be concluded that although glucagon depresses serum FFA concentration in vivo by stimulating insulin and glucose release, under suitable circumstances, its lipolytic effect can be demonstrated by a rise in serum FFA. A dose of insulin, as small as 0.5 mU/kg, which caused little change in serum glucose, was found to be effective in reducing serum FFA concentration. This amount of insulin may be present in commonly used doses of cystalline glucagon and may contribute significantly to their biologic effects. The prompt and potent insulogenic action of glucagon in vivo was confirmed. Three to 4 days after total pancreatectomy, serum IRI had decreased but had not disappeared. In these animals, the IRI response to glucagon could not be demonstrated.