Calcium augments hypoxic vasoconstriction in lungs from high-altitude rats

Abstract

Isolated lungs from high-altitude rats compared to those from low-altitude rats have blunted hypoxic pressor responses. Because Ca is essential for the hypoxic pressor response and since Ca is altered in the pulmonary arterial smooth muscle during high-altitude exposure, altered Ca metabolism might account for the blunted response. Differences between high- and low-altitude rat lungs in response to altering extracellular Ca were studied. Addition of Ca to the blood perfusate augmented the hypoxic pressor response of high-altitude lungs and depressed that of low-altitude lungs. Ca addition did not affect pressor responses to angiotensin II, but slowed vasodilation after both angiotensin injection and removal of the hypoxic stimulus. Maximal KCl-induced contraction was blunted in rings of main pulmonary artery from high-altitude rats, but augmented in their aortic rings. Submaximally constricted (40 mM KCl) pulmonary arteries from low- but not high-altitude rats further constricted with Ca addition. Aortic rings exhibited an inverse behavior. Ca addition augmented the blunted vasopressor response in high-altitude rat lungs, possibly by an effect on lung arteries. The aorta and main pulmonary artery differ in Ca handling.