ABSTRACT. The purpose of this study was to determine alkalosis reduces hypoxia-induced pulmonary vasoconstriction whether metabolic and respiratory alkalosis reduce hy-in lungs of a newborn animal. We also wanted to determine if poxia-induced pulmonary vasoconstriction in lungs of new-metabolic and respiratory-induced alkalosis have similar effects born rabbits. To accomplish this, we isolated and perfused on hypoxic pulmonary vaosconstriction. Finally, we wondered with blood the lungs from 33 newborn rabbits, 3-14 d old. if inducing alkalosis during versus before exposure to hypoxia In all pairs of lungs, we first measured the magnitude of would produce different results. To accomplish these goals, we hypoxia-induced pulmonary vasoconstriction a t a p H of first measured the magnitude of hypoxia-induced pulmonary 7.30-7.42. We then measured the effect of alkalosis on the vasoconstriction at a pH of 7.30-7.42 in isolated, perfused lungs magnitude of hypoxic pulmonary vasoconstruction by fol-of newborn rabbits. Next, in some lungs we repeated the hypoxic lowing one of two different sequences of exposure to hy-challenge and during hypoxia induced respiratory or metabolic poxia and alkalosis. For the first sequence, we exposed 13 alkalosis. In other lungs, we induced respiratory or metabolic lungs to hypoxia, and during the hypoxic exposure we alkalosis and then repeated the hypoxic challenge. We found that either decreased the inspired Pcoz (respiratory alkalosis, n both metabolic and respiratory alkalosis decreased the magnitude = 8) or infused N a H C 0 3 (metabolic alkalosis, n = 5) to of hypoxia-induced pulmonary vasoconstriction when alkalosis achieve a p H of 7.50-7.65. For the second sequence, we was induced during the hypoxic challenge. In contrast, when first decreased the inspired Pco2 (n = 9) or infused Na-either mode of alkalosis was induced before hypoxia, pulmonary H C 0 3 (n = 11) to achieve a p H of 7.50-7.65 and then arterial vasoconstriction was not decreased. We conclude that exposed the lungs to hypoxia. We found that hypoxic respiratory and metabolic alkalosis have similar effects on hypulmonary vasoconstriction was reduced by either respi-poxia-induced pulmonary vasoconstriction in lungs of newborn ratory or metabolic alkalosis, when alkalosis was induced rabbits. Both types of alkalosis reduce ongoing hypoxic pulmoduring hypoxia. When respiratory or metabolic alkalosis nary vasoconstriction, and neither diminishes vasoconstriction was induced before hypoxia, the magnitude of hypoxia-in response to subsequent hypoxia. induced pulmonary vasoconstriction was the same as at the normal pH. We conclude that both metabolic and respira-MATERIALS AND METHODS tory alkalosis reduce ongoing hypoxic pulmonary vasoconstriction in lungs of newborn rabbits. However, neither Surgicu/prepurution. We anesthetized 33 New Zealand White mode of alkalosis blunts pulmonary vasoconstriction in newborn rabbit Pups, ages 3-14 d, wt 148 + 52 g, with sodium response to subsequent exposures to hypoxia. (Pediatr Res pento...