Effect of pH on pulmonary vascular tone, reactivity, and arachidonate

tone, reactivity, and arachidonate metabolism. J. Appl. Physiol. 67(l): 445-452, 1989.-We studied the effects of perfusate pH on pulmonary vascular tone, reactivity, and thromboxane and prostacyclin synthesis in isolated buffer-perfused rabbit lungs. Extracellular acidosis did not affect base-line vascular tone, but alkalosis had a biphasic effect. Increasing the perfusate pH from 7.40 to 7.65 caused vasodilation, whereas raising pH to 7.70-8.10 caused vasoconstriction. Removing calcium ( Ca2+) from the perfusate completely prevented the vasoconstriction caused by alkalosis. Perfusate pH strikingly affected pulmonary vascular reactivity. Acidosis inhibited the vasoconstriction caused by thromboxane and potassium chloride (KCl) but did not affect the response to angiotensin II. Alkalosis, in contrast, augmented the vasoconstriction caused by thromboxane and angiotensin II but reduced the vasoconstriction caused by KCl. Changes in pH also altered thromboxane and prostacyclin synthesis after the infusion of exogenous arachidonic acid (AA) or the endogenous release of AA by the lipid peroxide tert-butyl hydroperoxide. hydrogen ion concentration; arachidonic acid; calcium; angio-tensin II; thromboxane A2; prostacyclin CHANGES IN pH may affect pulmonary vascular smooth muscle tone (19, 28, 31). Most previous pulmonary re-ports have focused on the effect of pH on hypoxic pul-monary vasoconstriction. To better understand mecha-nisms by which pH can affect basal pulmonary vascular tone and reactivity, we studied the effects produced by a broad range of pH in buffer-perfused isolated rabbit lungs. Because H+ concentration can influence Ca2 ’ in