Gas diffusive conductance of sea-level hen eggs incubated at 2900 m altitude.

Sea level hen eggs, selected for their shell conductance (water vapor conductance, HH2O), were incubated at a simulated high altitude, PB = 529 Torr, ca. 2900 m, at 72% relative humidity (rh) to prevent excessive water loss due to hypobaric condition; they were transferred to 150 m 18-24 h before measurements. Control eggs were incubated at 150 m, PB = 750 Torr, rh = 60%. In 8- to 18-day embryos, total CO diffusive conductance, GCO; embyronic body mass, BM; oxygen consumption, MO2; blood hematocrit, Hct; hemoglobin concentration, [Hb]; and heart mass, HM, were measured. Total water loss was the same in both groups, 12% initial egg mass. However, the severe effects of high altitude: 72% mortality and 9% malformation, and reduced increases of BM and MO2, can be related partially to the strong hypocapnia, which resulted from the high shell conductance (GH2O = 18.1 mg X (d X Torr)-1, and was superimposed on the hypoxia. GCO was reduced, while Hct, [Hb] and HM were not significantly affected. When measurements were normalized to BM, MO2 and GCO were identical in the two groups, whereas [Hb] and HM were higher at 2900 m (differential growth). Thus, during incubation, gas diffusive conductance appeared to depend on embryo development and did not adapt to altitude hypoxia. Compared with controls, GCO in high-altitude eggs actually decreased in proportion to BM growth.