LUNG ENDOTHELIAL-CELL PROLIFERATION IN NORMAL AND PULMONARY HYPERTENSIVE NEONATAL CALVES

Tremendous changes in pressure and flow occur in the pulmonary and sys temic circulations after birth, and these hemodynamic changes should m arkedly affect endothelial cell replication. However, in vivo endothel ial replication rates in the neonatal period have not been reported. T o label replicating endothelial cells, we administered the thymidine a nalog bromodeoxyuridine to calves similar to 1, 4, 7, 10, and 14 days old before they were killed. Because we expected the ratio of replicat ing to nonreplicating cells to vary with vascular segment, we examined the main pulmonary artery, a large elastic artery, three sizes of int rapulmonary arteries, the aorta, and the carotid artery. In normoxia f or arteries < 1,500 mu m, similar to 27% of the endothelial cells were labeled on day 1 but only similar to 2% on day 14. In the main pulmon ary artery, only similar to 4% of the endothelial cells were labeled o n day 1 and similar to 2% on day 14. In contrast, in the aorta, simila r to 12% of the endothelial cells were labeled on day 1 and similar to 2% on day 14. In chronically hypoxic animals, only similar to 14% of the endothelial cells were labeled on day 1 in small lung arteries and similar to 8% were still labeled on day 14. We conclude that the post natal circulatory adaptation to extrauterine life includes significant changes in endothelial cell proliferation that vary dramatically with time and vascular location and that these changes are altered in chro nic hypoxia.