Chronic hypoxia impairs pulmonary venous smooth muscle contraction

Chronic hypoxia increases total pulmonary vascular resistance and causes pulmonary hypertension. Although the effect of chronic hypoxia on pulmonary arterial tissue has been extensively studied, very little is known about the effects on the pulmonary vein. The purpose of the present investigation was to determine the effect of chronic hypoxia on pulmonary venous reactivity to several vasoactive agonists and on the venous response to acute hypoxia. Isolated pulmonary venous rings were taken from rats exposed to 2, 7, and 14 days of hypoxia (FIO2 = 0.1). A decrease in the response of the pulmonary vein to KCl was observed after 14 days of hypoxia. The reactivity (maximum active force produced) of the pulmonary vein in response to phenylephrine (PE) was reduced after 7 days of hypoxia. The response of the pulmonary vein to angiotensin II (AII) was more sensitive to the effects of chronic hypoxia since decreased reactivity to angiotensin II occurred after only 2 days of hypoxia. Prolonged hypoxia (14 days) had no further effect on the decreased reactivities to PE and AII. The sensitivities of pulmonary venous muscle to PE and AII were decreased (increased ED50 values) by 2 days of chronic hypoxia, but tended to return to control levels after 7 and 14 days of hypoxia. However, the contractile response of the pulmonary vein to acute hypoxia was not changed even after 14 days of chronic hypoxia. These results suggest that chronic hypoxia: (1) impairs pulmonary venous smooth muscle contractility; (2) reduces pulmonary venous reactivity and sensitivity to phenylephrine and angiotensin II; and (3) does not alter the pulmonary venous contractile response to acute hypoxia.