Studies on the Mechanism of Insulin Antagonism by Albumin in Rat Diaphragm

Abstract

Utilizing a modification of the rat diaphragm technic, studies of the mechanism of action of the albumin-associated antagonist were carried out using human fraction V. It was demonstrated that the antagonist could not be washed off of the diaphragm, that prior exposure of the diaphragm to insulin did not fully protect it from subsequent antagonism of the insulin effect and that, although antagonism was proportional to albumin concentration, large excesses of insulin could not completely overcome small concentrations of the antagonist. The intracellular accumulation of AIB was inhibited by the antagonistic albumin but not by a nonantagonistic one (bovine fraction V). Both albumins depressed radioactive glycine incorporation into muscle protein. The antagonist was shown to inhibit glucose uptake much more than glycogen synthesis.These data indicate that the albumin-associated antagonist primarily blocks insulin effects on transport by either an extremely strong binding to the muscle cell or an irreversible alteration of the diaphragm's response to insulin without binding. DIABETES J5: 373-79, June, 1966. Factors extraneous to the pancreas were first implicated in the pathogenesis of diabetes mellitus by the classical experiments of Houssay and Biasotti 1 who were able to produce an amelioration of the diabetic state by hypophysectomy in dogs. The demonstration that adrenalectomy also alleviates the severe diabetes caused by total pancreatectomy soon followed. 2 ' 3 When purified growth hormone became available, diabetes mellitus could be produced in normal cats 4 and dogs 5 by administration of this hormone. More recent evidence has been the demonstration of increased levels of circulating insulin in untreated adult-onset and early cases of juvenile diabetes by immunoassay, 6 rat diaphragm' 1 ' and adipose tissue 8 assays. All of this suggests From the Robert H.

Effect of Free Fatty Acids and Insulin on Protein Synthesis and Amino Acid Metabolism of Isolated Rat Diaphragms

“…per cent bovine serum albumin has been reported, and attributed to nonspecific amino acid competition. 13 The addition of 3 mM. palmitate to a medium containing albumin decreased the incorporation of C-14 from glycine or histidine into proteins.…”

Effect of Antagonistic Albumin on Insulin-stimulated Intracellular Metabolic Pathways

“…It can be removed from albumin by boiling for five minutes, by extracting with chloroform, ethanol, or glacial acetic acid in iso-octane, 11 and by passage through either cellulose 12 or Sephadex. 1 The antagonist has also been shown to decrease insulin-stimulated lactic acid production 14 -15 and lipid synthesis 15 in rat diaphragm but these effects can not be separated from its primary action on glucose transport. In vitro, the albumin antagonist is firmly bound to the rat diaphragm,* inhibits glucose transport in a noncompetitive manner, blocks AIB transport and RNA synthesis, but does not depress the glycogen synthetic pathway.…”