Glucagon and insulin from lean rats and genetically obese fatty rats: Studies by radioimmunoassay, radioreceptorassay and bioassay

Abstract

Insulin, proinsulin and glucagon extracted from lean rat pancreases were studied in radioimmunoassay, radioreceptorassay and bioassay systems. Extracted insulin behaved identically to a rat insulin used as a reference standard in radioimmunoassay. On the basis of its immunoreactivity, extracted insulin was slightly less potent (about 70%) than the rat standard insulin in competing with the binding of¹²⁵I-insulin to rat liver membranes (radioreceptorassay) and in stimulating glucose oxidation by rat fat cells (bioassay). Extracted glucagon and a pork glucagon used as a reference standard were indistinguishable in two radioimmunoassay systems for glucagon, in competing with the binding of¹²⁵I-glucagon to rat liver membranes (radioreceptorassay) and in stimulating adenylate cyclase in rat liver membranes (bioassay). Genetically obese rats (Zucker, “fatty”) were compared to their lean littermates with respect to insulin, proinsulin and glucagon extracted from their pancreases. Proinsulin represented the same proportion of total immunoreactive insulin in both types of rats. In the radioimmunoassays, the radioreceptorassays and the bioassays, insulin, proinsulin and glucagon from obese rats were indistinguishable from insulin, proinsulin and glucagon from lean rats. It is concluded that the pancreatic hormones of obese (“fatty”) rats possess the same immunoreactivity and biological potency as those of nonobese rats. This excludes the possibility that some alteration in the biological properties of pancreas insulin and/or glucagon of fatty rats could explain the metabolic abnormalities observed in this type of obesity.