Effects of hypoxia on tissue capillarity in geese

Tissue capillarity in the gastrocnemius and myoglobin concentrations in the gastrocnemius and heart were determined for hatchling Canada geese, Branta canadensis, following incubation of the embryos under either normoxic (Po2 = 120 torr) or hypoxic (Po2 = 94 torr) conditions. Similar observations were made on a limited number of hatchling bar-headed geese, Anser indicus, a species native to high altitude. Capillary densities were higher and diffusion distances shorter in the hypoxic Canada geese and the bar-headed geese than in the normoxic Canada geese. The concentrations of myoglobin in the heart and gastrocnemius increased with mass, but not as a function of hypoxia. We conclude that bird embryos respond to hypoxia by increasing capillarity. The increased capillarity is found in species native to high altitude when incubated under conditions of normoxia and can be induced in species native to sea level by exposure to hypoxia during development.