In the defence against hyperglycaemia: an avian strategy

Birds live longer than mammals of comparable sizes, contrary to what their metabolic rates, plasma glucose concentrations and body temperatures, all o f which are higher than mammalian norms, would suggest. Although these fact ors should predispose them to accelerated tissue degeneration, this has bee n shown not to happen. In this paper the possible mechanisms whereby birds limit the accelerated tissue damage that should be associated with the abov e characteristics are explored. Specifically, this review will focus on the relationship in chickens between the raised concentrations of plasma gluco se and the lack of associated tissue complications. We propose that the rol e of uric acid in birds should be re-examined. Until now uric acid has been considered to be little more than an excretory by-product where its role a s an antioxidant can be directly linked to the resistance of birds to gluco se-mediated tissue damage. It is suggested that, compared with mammals, the lower rate of generation of reactive oxygen species in birds in associatio n with their stronger antioxidant-defence system contributes to their longe vity.