No abstract

No abstract

Prolonged fasting caused a rise in blood glucose which reached a maximum above the prefast level on the 6th day. Concurrently the liver glycogen, rapidly depleted at the start of the fast, was partially replaced. Blood NPN increased continuously. Thus, gluconeogenesis appeared likely not only to be responsible for the blood glucose increase but also to play a role in the restoration of liver glycogen after initial glycogenolysis due to fasting. Fasting for 48 hours increased cardiac glycogen up to three times the prefasting level; a rapid decrease in this moiety occurred with further abstinence. Glucagon and growth hormone increased the cardiac glycogen of nonfasted birds; but had little, if any, influence on the effects of fasting. The daily injection of 60–70 u of either regular or HGF-free insulin per kilogram body weight resulted in an hyperglycemic rebound 24 hours after each injection. This rebound could be blocked completely by feeding Dibenzyline.

istorical Background. Of the four recognized peptide hormones secreted by the endocrine pancreas, pancreatic polypeptide (PP) was the third to be discovered, isolated, and characterized. Insulin ( 192 1-22) and glucagon ( 1923) preceded and somatostatin ( 1975) followed the isolation of PP in 1968. Despite this sequence of events-and the time interval since its discovery-PP remains somewhat of an enigma both in name and in function. The reluctance to label this polypeptide with a more descriptive title than the lackluster PP it bears stems largely from the fact that while broad actions may be attributed to it, no outstanding or dominating effect has been identified with its actions. Thus, the only characteristic carried by use of the phrase PP is to signify the species of PP one is discussing, such as avian, bovine, rat, porcine, ovine, and human, for example. The avian structure has 15 identities (of a total of 36) with that of bovine PP, and the latter differs by one or two residues from most other mammalian PP at any of three or four positions within the molecule. Thus, strong structural conservatism exists from an evolutionary point of view.The consideration that a family of pancreatic polypeptides exists is not unique within the field of physiologic chemistry, as it has been well recognized that many other polypeptides of interest are structurally related, are well conserved, and have overlapping physiological actions, and yet also may express distinctly ' To whom requests for reprints should be addressed

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)