Pancreatic hormones, insulin/glucagon molar ratios, and somatostatin as determinants of avian carbohydrate metabolism.

The endocrine pancreas of birds contains cell populations similar, if not identical, to those found in mammalian pancreata, although the topographical distributions of these cell types differ to some extent. Insulin-secreting (B) cells, glucagon-secreting (A) cells, somatostatin-secreting (D) cells, and pancreatic polypeptide-secreting (PP or F) cells are distributed unequally among the four pancreatic lobes, with most of the A cells located in the third and splenic lobes and PP cells residing in both islet tissue and in acinar tissue. Glucagon appears to be a (the?) major pancreatic hormone involved in metabolic glucoregulation in birds. Yet the essentiality of insulin for this regulatory purpose also has been established. As a result, current thought is directed toward the molar ratio of insulin to glucagon (I/G) as a dominant force in homeostasis rather than toward either of the two hormones separately. Molar I/G ratios have been useful in mammals in studying the needs of the organism to produce glucose to meet a metabolic crisis/need and, when compared with that found in normal Aves, a value of 1.8-2.2 has been established. Such a molar ratio is indicative of a catabolic recovery of nutrients in mammals, suggesting that birds normally are in a catabolic mode (like diabetic, starving, or exercising mammals). Somatostatin (SRIF) is known to inhibit the release of all pancreatic hormones but has a greater inhibitory action on glucagon secretion than it does on any of the other peptides. (It has least effect on APP).(ABSTRACT TRUNCATED AT 250 WORDS)