Meeting Abstract
Birds catabolize protein along with energy- dense lipids to meet the intensive metabolic demands of migration which leads to significant organ atrophy in small songbirds. Consequential reductions in gastrointestinal tissue- as great as 50%- initially constrain refueling rate during stopover, yet birds are able to regain digestive performance within a short period of time. To aid in the rebuilding of lean tissues after flight, birds must maintain the ability to digest and assimilate protein, despite reduced intestine mass. Aminopeptidase-N (APN) is a brush-border enzyme responsible for cleaving amino acids from peptides and is necessary during the final stage of protein digestion and absorption. The aim of this study was to determine if migratory passerines dynamically regulate APN to prioritize the assimilation of protein during simulated migration and stopover. We hypothesized birds recovering from a fast would upregulate APN activity to quickly process and integrate dietary protein into lean mass. We fasted 25 wild-caught migratory white-throated sparrows (Zonotrichia albicollis) for 48h to mimic fat and lean mass reductions experienced during flight, and measured intestinal APN activity before the fast, after the fast, 24 hours post fast, and 48 hours post fast. Total fat mass, lean mass, and basal metabolic rate (BMR) were measured daily. Our data reveals that fasted birds maintain APN activity through the fast, despite a 30% reduction in intestine mass, and during refueling birds increase APN activity nearly two-fold over pre-fasted individuals. This suggests that APN is preferentially maintained during fasting and dynamically up-regulated to meet the increased protein demand during migratory stopover.
