Pulmonary artery structural changes in two colonies of rats with different sensitivity to chronic hypoxia.

Chronic hypoxia causes more severe pulmonary hypertension in the Hilltop colony of Sprague-Dawley rats than in the Madison colony and also greater polycythemia and vasoconstriction. This study examines the structural features of the pulmonary artery bed, another contributing factor to hypoxic hypertension. After 14 days of hypobaric hypoxia, in Hilltop rats, more of the intraacinar arteries became muscular, and the medial thickness of intraacinar and preacinar arteries was greater. In Hilltop control rats, muscle was found in more intraacinar arteries, but, paradoxically, acute hypoxic vasoconstriction was less. Thus, while in chronic hypoxia increased muscle correlates with pulmonary hypertension, in control rats the reserve seems to be true. The increased muscle in control Hilltop rats could, however, predispose to the greater muscularization seen after chronic hypoxia.