CHARACTERIZATION OF INSULIN-RECEPTORS IN CHICKEN KIDNEYS - EFFECT OF NUTRITIONAL-STATUS

In chickens, the kidneys actively contribute to gluconeogenesis. A cyt osolic form of phosphoenolpyruvate carboxykinase (PEPCK) is present in this tissue but is absent in liver. Cytosolic renal PEPCK is nutritio nally 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 chicke n. The effects of the following nutritional conditions were examined: fed, 48 hr fasted, and 24 hr refed following a 48-hr fast. PEPCK activ ity was increased by the 48-hr fast and returned to normal after refee ding. Specific binding of I-125-insulin to renal membranes was time-, temperature-, and protein-dependent. Unlabeled insulin was more potent than IGF-1 in inhibiting I-125-insulin binding; the ratio of potencie s for insulin and IGF-1, however, was dependent upon the nutritional s tate. Insulin binding was significantly higher (P < 0.05) following 48 hr fasting and lower (P < 0.05) following refeeding compared to ad li bitum feeding. Receptor affinity was similar irrespective of the nutri tional state. Solubilized and wheat germ agglutinin purified renal ins ulin receptors were devoid of ATPase activity in contrast to hepatic r eceptors. The sizes of alpha- and beta-subunits of renal receptors wer e similar to those of hepatic receptors: 135 and 95 kDa, respectively. Insulin-stimulated autophosphorylation of the beta-subunit was decrea sed, although not significantly, by prolonged fasting. Phosphorylation of artificial substrate: poly(Glu-Tyr) 4:1 was significantly decrease d by the 48-hr fast at high insulin concentrations (10 and 100 nM). Ki nase activities of renal insulin receptors from fed or refed chickens were very similar. In conclusion, typical insulin receptors are presen t in chicken kidneys. These receptors exhibit a regulation at the leve l of their number and kinase activity in a fashion similar to that fou nd for hepatic receptors. The present results suggest a role for insul in in chicken renal function. (C) 1994 Academic Press, Inc.