Preliminary examination of a role for insulin in the regulation of glucose excretion in mourning doves (Zenaida macroura)

Abstract

Birds have naturally high plasma glucose (PGlu) concentrations and are resistant to the effects of insulin such that high doses must be given to achieve a significant reduction of glucose. In mammals insulin lowers PGlu by increasing uptake into skeletal and cardiac muscle as well as adipose tissues. However, prior studies have shown that high doses of insulin were ineffective at increasing glucose uptake into these tissues or into the kidneys of mourning doves (Zenaida macroura) despite significant decreases in PGlu. In addition, several case studies have shown a correlation between PGlu and urine glucose concentrations in birds. Therefore, the hypothesis of the present study was that insulin lowers PGlu in birds by augmenting renal glucose excretion. Adult male mourning doves were anesthetized using sodium pentobarbital. The brachial vein was cannulated for administration of [C14]‐inulin and insulin and the brachial artery was cannulated for blood collections. Ureteral urine was collected via a catheter inserted into the cloaca. Insulin (400 μg/kg body mass, i.v.) significantly decreased PGlu (p=0.0199) and increased glomerular filtration rate (p=0.0137), urine flow rate (p=0.0074), glucose excretion (p=0.0084) as well as fractional excretion of glucose (p=0.0038) by the kidneys. The findings from the present study suggest for the first time that the mechanism of insulin‐mediated glucose homeostasis in birds is more complex than previously thought and may include glucose excretion in urine. To our knowledge this mechanism of insulin‐mediated glucose excretion has not been demonstrated in other vertebrates.