Effects of chronic hypoxia on structure and reactivity of rat lung microvessels.

The reactivity of lung microvessels is determined by a method based on planimetry of elastic laminae (EL) in vessel cross sections. Because wall structure is assessed, arteries that undergo remodeling during chronic hypertension can be identified. To study the structure and reactivity of such vessels, slices obtained from lungs of six rats exposed to hypobaric hypoxia for 14 days and from normoxic controls were incubated in culture with 10(-4) M l-epinephrine (EPI), then fixed and processed for microscopy. For muscular arteries (less than 200 microns diam), the circumferential length of internal EL (IEL) is positively correlated with length of external EL (EEL). In larger arteries, EEL is shorter than IEL and may restrict distension, but in smaller arteries the converse is true. After chronic hypoxia, the regression line shifts, indicating structural remodeling. For newly muscularized arteries found only after hypoxia the new IEL is always shorter than EEL, and a complex network of elastin connects the two. Muscular arteries constrict with EPI to the same degree after hypoxia as after normoxia. Nonmuscular vessels (arteries and veins) also constrict similarly after either exposure regimen. For newly muscularized arteries of the same size and location as the nonmuscular vessels, the response is significantly less.