Chronic hypoxic pulmonary hypertension in rats and increased elastolytic activity.

Previously in rats injected with the toxin monocrotaline and administered SC-39026, a serine elastase inhibitor, pulmonary hypertension was decreased in association with reduced muscularization of peripheral pulmonary arteries. To determine whether inhibition of elastolytic activity might prevent this vascular change in other conditions producing pulmonary hypertension, we administered SC-39026 to rats during a 10-day exposure to chronic hypobaric hypoxia. We also measured elastolytic activity in the central pulmonary arteries of rats using [3H]elastin substrate and determined whether there was an increase in activity either as early as 2 days or at completion of the hypoxic exposure, which could be inhibited by SC-39026. to further determine whether the mechanism of muscularization of peripheral arteries is modulated by degradation of elastin or other elastase-susceptible extracellular matrix proteins, we assessed desmosine excretion and ultrastructural alterations in elastin as well as in type IV collagen, fibronectin, and laminin. SC-39026 reduced the number of muscularized arteries and the level of pulmonary arterial pressure during exposure to chronic hypoxia. Elastolytic activity was fourfold higher in central pulmonary arteries 2 days after hypoxia when compared with values in control vessels, and the activity was inhibited by SC-39026. In small peripheral pulmonary arteries there were no significant changes with hypoxia reflected in desmosines or in the immunocytochemistry of elastase-susceptible glycoproteins, with the exception of decreased laminin. This feature was not inhibited by SC-39026. To further assess whether the protective effect of SC-39026 was related to its inhibition of elastase, an extended study was carried out using a different elastase inhibitor, alpha 1-proteinase inhibitor. An even greater reduction in hypoxia-induced pulmonary hypertension and vascular changes was observed with this elastase inhibitor and the latter included medial hypertrophy.