Putative role for insulin in glucose regulation by avian kidneys

Abstract

Birds have naturally high blood glucose concentrations. Prior studies of mourning doves (MODO) have shown that supraphysiological doses of insulin mildly, but significantly, decrease blood glucose levels. However, glucose uptake was not increased into tissues typically associated with insulin‐mediated glucose uptake (i.e. skeletal muscle, adipose tissue or cardiac muscle), nor was uptake increased in kidney, liver or brain tissues. These findings demonstrate that MODO are resistant to insulin‐mediated glucose uptake. Therefore, the goal of the present study was to test the hypothesis that insulin exerts a hypoglycemic role by augmenting glucose excretion by the avian kidney. Using a polyclonal rabbit antibody against the alpha‐subunit of the insulin receptor, western blots were performed on isolated kidneys from adult male MODO. The results supported the hypothesis that the avian kidney expresses the insulin receptor. In contrast to birds, others have shown that expression of the insulin receptor in mammals is downregulated with insulin resistance. As mentioned, glucose uptake into MODO kidneys is not enhanced in response to insulin. The presence of the insulin receptor in MODO kidneys, therefore, suggests a potential role for insulin in the regulation of glucose homeostasis through excretion. Further studies are aimed at elucidating this role of insulin.