INSULIN-RECEPTOR CONTENT IN TISSUES OF NORMAL AND DIABETIC RATS MEASURED BY RADIOIMMUNOASSAY

Insulin receptor (1R) content in different tissues has been quantitati vely evaluated by means of steady state binding studies with radiolabe led insulin. The information provided by this approach, however, does not give a direct measurement of the receptor protein. Rather, it depe nds on the binding function of the IR, evaluated on the basis of curvi linear plots derived by Scatchard analysis of the experimental data. I n the present report we employed a sensitive and specific radioimmunoa ssay (RIA) that allows a direct measurement of IR in solubilized cells or tissues. By this method we studied: a) IR distribution in several tissues of the rat, the animal model most frequently used in studies o f insulin action; b) IR regulation in streptozotocin-treated, diabetic insulin deficient rats. Tissues from male Wistar rats (11 controls an d 6 streptozotocin-treated diabetic animals) were homogenized, solubil ized with Triton X-100 in the presence of protease inhibitors and stor ed at -80 C. IR content in the solubilized material was then measured by RIA. IR were detectable in all 11 tissues tested. Liver, kidney and brain neocortex had the highest IR content. (24.7+/-1.0, 20.5+/-1.1, 25.9+/-1.6 ng/mg protein, m +/- SE, respectively). As expected, circul ating insulin levels were lower in diabetic rats than in control rats. In diabetic, insulin deficient rats, liver, kidney and skeletal muscl e contained more IR than in control rats (p = 0.001; p = 0.018; p = 0. 003, respectively), whereas IR content in neocortex was similar in the two groups. The IR RIA may represent a useful tool for the study of I R regulation and pathophysiology. Our data provide a comparative direc t measurement of IR distribution in a variety of rat tissues. IR conte nt in diabetic rats is increased in typical target organs for insulin action, as a consequence of up-regulation due to the reduced insulin l evels. This is not the case for metabolically insulin-dependent tissue s, like brain. (C) 1996, Editrice Kurtis