Glucagon

Abstract

Until three decades ago, glucagon received very limited attention. Perhaps the greatest obstacles in early glucagon research were conceptual, and based on mammalian bias. The main arguments against the existence of an insular hyperglycemic-glycogenolytic hormone were that (a) no related deficiency syndromes were noted after pancreatectomy, and (b) there appeared to be no need for a hormone duplicating the functions of epinephrine. However, it now appears that the overlapping (but not redundant!) actions of glucagon and epinephrine may provide a critical safety mechanism against the devastating effect of hypoglycemia in mammals (see e.g., P. E. Cryer et al. 1984; Sperling et al. 1984), and that some vertebrate groups may depend more on glucagon than on insulin in their regulations of metabolism of carbohydrate (birds and Squamata) and lipid (birds) (see below). Nevertheless, even in mammals some basic questions as to the role of glucagon in glycemic regulations of mammals are still disputed (cf. Tan et al. 1985). There seems to have been no account of the comparative physiology of glucagon since the reviews by Plisetskaya (1975) and Epple et al. (1980). On the other hand, many important contributions on the basic and mammalian physiology of glucagon are contained in two recent volumes edited by Lefèbvre (1983a, b).