Influence of flight on protein catabolism, especially myofilament breakdown, in homing pigeons

In order to study protein degradation during flight in homing, a high-performance liquid chromatography technique was developed for the quantitative analysis of Nτ-methylhistidine. Secondly, it was necessary to confirm that the excretion of Nτ-methylhistidine correlates with myofilament breakdown in homing pigeons. In these experiments, ten birds were subcutaneously injected with Nτ-[14C]methylhistidine and the excreta were quantitatively collected for 1 week. Of the 94.5% radioactivity recovered, 87.1% was associated with Nτ-[14C]methylhistidine and 6.1% with N-acetyl-Nτ-[14C]methylhistidine. This rapid excretion of unmetabolized Nτ-[14C]methylhistidine validates the assumption that the amount of Nτ-methylhistidine excreted is a measure of myofilament catabolism in homing pigeons. The influence of endurance flight on protein breakdown was determined after flights from release sites 368–646 km away. Immediately after return, plasma urea and uric acid levels were increased, whereas plasma concentration of Nτ-methylhistidine remained unchanged compared to unflown control birds. Flown pigeons excreted significantly more urea and Nτ-methylhistidine within 24 h and significantly more urea and uric acid within 96 h after flight than unflown controls. Our findings support the hypothesis that in homing pigeons protein catabolism is increased during endurance flight. Elevated Nτ-methylhistidine excretion probably results from repair processes in damaged muscle fibers, including breakdown of myofilaments.