Lung vascular cell proliferation in hyperoxic pulmonary hypertension and on return to air: [3H]thymidine pulse-labeling of intimal, medial, and adventitial cells in microvessels and at the hilum.

The labeling index (LI) of lung vascular intimal (endothelial and precursor smooth muscle, medial (smooth muscle), and adventitial cells (fibroblasts) was in the normal rat and in the rat with pulmonary hypertension caused by breathing high oxygen (87% O2 at normobaric pressure). Cell labeling was assessed during hyperoxia (Days 1, 4, 7, 10, and 28), at the start and end of weaning hyperoxia-adapted rats to air (Days 29 and 35), and 1, 2, and 4 wk after return to breathing air after hyperoxia and weaning (Days 42, 49, and 63). Bursts of intimal, medial, and adventitial cell proliferation different in their timing and extent contribute to lung vascular wall remodelling in these injuries. The Ll of the microvascular fibroblast increased most on Day 4 of hyperoxia (20-fold); it persisted above the normal rate throughout hyperoxia and was high at the start of weaning (greater than 1- less than 2-fold). Two weeks after return to breathing air, it again increased (less than 1-fold). The Ll of the microvascular endothelial cell increased most on Day 7 of hyperoxia (10-fold); it also persisted above the normal rate throughout hyperoxia and at the start of weaning (greater than 2- less than 3-fold) and increased again 2 wk after return to breathing air (6-fold). Labeled precursor cells were not present in the normal lung: they were present on Days 4 and 7 of hyperoxia but not at any other time, including weaning and return to breathing air.(ABSTRACT TRUNCATED AT 250 WORDS)