ULTRASTRUCTURAL DIFFERENCES BETWEEN PULMONARY ARTERIOLAR MUSCULARIZATION INDUCED BY HYPOXIA AND MONOCROTALINE

A group of Wistar rats was treated with two subcutaneous injections of monocrotaline, at 4 and 6 weeks of age. They were then killed 1 month after the initial injection. A second group of rats was born and rear ed in hypobaric hypoxia for 1 month before being killed. Both groups h ad age-matched controls. The ultrastructure of pulmonary arterioles fr om all groups was studied, and quantitative measurements were made of the volume densities of organelles within the cytoplasm of arteriolar smooth muscle cells. The pulmonary arterioles of rats treated with mon ocrotaline contained immature smooth muscle cells with coarse peripher al myofilaments and were bounded by thin indistinct elastic laminae. I n contrast, the arteriolar smooth muscle cells of hypoxic rats were ma ture with fine myofilaments and bounded by electron dense laminae. Whe n compared with both their respective controls and the alternative tes t group, the muscle cells from rats treated with monocrotaline had sig nificantly lower volume densities of dense bodies, and the hypoxic mus cle cells had significantly higher densities of mitochondria. The pulm onary arteriolar muscularization in rats would appear to be a nonunifo rm process producing smooth muscle cells with differing cytoplasmic fe atures that suggest differing cellular functions. (C) 1994 Academic Pr ess, Inc.