Do Birds Manage Free-radicals More Effectively Than Mammals?

Abstract

The free radical theory of ageing proposes that organisms age due to the accumulation of oxidative cell damage by free radicals (ROS) over time. Animals with high rates of metabolism produce more free radicals and are more susceptible to oxidative damage. Despite having profoundly higher basal metabolic rates and lifetime energy expenditures, birds age significantly slower than mammals of similar size. This project aimed to determine whether birds age slower than mammals due to 1) lower mitochondrial free radical production or 2) increased mitochondrial consumption of free radicals. The activity of heart fibres from Zucker rats (Rattus norvegicus) and Rock Pigeons (Columba livia) was compared with OroborosTM oxygraph assays by 1) measuring free radical production at physiological relevant conditions - utilising a full multi substrate-inhibitor assay and at 37°C and 42°C for the rat and pigeon respectively; 2) measuring uptake of free radicals by heart fibres also at these temperatures. A greater ROS production from rat fibres while respiring on succinate was the only significant difference between the two animals in this aspect of their biology. Additionally, there was no significant difference in the capacity of heart fibres from each animal to consume ROS. This could mean mitochondria differ from the current paradigm of net ROS producers and other aspects of avian biology such as antioxidant defense systems should be examined in a comparative context. This study contributes to a growing body of research aimed at explaining the disparity in longevity between birds and similar sized mammals.