Characterization of insulin receptors in chicken kidneys: effect of nutritional status.

In chickens, the kidneys actively contribute to gluconeogenesis. A cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK) is present in this tissue but is absent in liver. Cytosolic renal PEPCK is nutritionally and hormonally controlled which indicates a likely contribution of insulin in the control of this enzyme (and other renal functions). The present studies characterize renal insulin receptors in the chicken. The effects of the following nutritional conditions were examined: fed, 48 hr fasted, and 24 hr refed following a 48-hr fast. PEPCK activity was increased by the 48-hr fast and returned to normal after refeeding. Specific binding of 125I-insulin to renal membranes was time-, temperature-, and protein-dependent. Unlabeled insulin was more potent than IGF-1 in inhibiting 125I-insulin binding; the ratio of potencies for insulin and IGF-1, however, was dependent upon the nutritional state. Insulin binding was significantly higher (P < 0.05) following 48 hr fasting and lower (P < 0.05) following refeeding compared to ad libitum feeding. Receptor affinity was similar irrespective of the nutritional state. Solubilized and wheat germ agglutinin purified renal insulin receptors were devoid of ATPase activity in contrast to hepatic receptors. The sizes of alpha- and beta-subunits of renal receptors were similar to those of hepatic receptors: 135 and 95 kDa, respectively. Insulin-stimulated autophosphorylation of the beta-subunit was decreased, although not significantly, by prolonged fasting. Phosphorylation of artificial substrate: poly(Glu-Tyr) 4:1 was significantly decreased by the 48-hr fast at high insulin concentrations (10 and 100 nM). Kinase activities of renal insulin receptors from fed or refed chickens were very similar. In conclusion, typical insulin receptors are present in chicken kidneys. These receptors exhibit a regulation at the level of their number and kinase activity in a fashion similar to that found for hepatic receptors. The present results suggest a role for insulin in chicken renal function.