Vascular hypertrophy in cattle susceptible to hypoxic pulmonary hypertension

Abstract

Differences in pulmonary vasoreactivity between cattle that were bred to be susceptible or resistant to development of severe pulmonary hypertension during hypoxia were examined. There may be greater production of endogenous dilator prostaglandin, and less hypoxic pulmonary vasoconstriction in the resistant cattle. Administration of an inhibitor of prostaglandin synthesis, meclofenamate, did not increase pulmonary pressor response to hypoxia in resistant cattle to the levels recorded in susceptible cattle, making the vasodilator prostaglandin hypothesis unlikely. The magnitude of pulmonary vascular response to prostaglandin F2.alpha., prostaglandin E1 and 5-hydroxytryptamine correlated with the response to hypoxia, suggesting that the degree of responsiveness was not selective for hypoxia. Varying degrees of lung arteriolar medial hypertrophy may account for differences in vasoreactivity to hypoxia and to vasoactive substances. Lung biopsies from 5 susceptible and 5 resistant calves showed greater medial arterial hypertrophy in susceptible calves. Susceptible calves may have more reactive pulmonary vessels than resistant calves because they have more vascular smooth muscle.