The effect of alkalosis on hypoxia-induced pulmonary vasoconstriction in lungs of newborn rabbits.

The purpose of this study was to determine whether metabolic and respiratory alkalosis reduce hypoxia-induced pulmonary vasoconstriction in lungs of newborn rabbits. To accomplish this, we isolated and perfused with blood the lungs from 33 newborn rabbits, 3-14 d old. In all pairs of lungs, we first measured the magnitude of hypoxia-induced pulmonary vasoconstriction at a pH of 7.30-7.42. We then measured the effect of alkalosis on the magnitude of hypoxic pulmonary vasoconstruction by following one of two different sequences of exposure to hypoxia and alkalosis. For the first sequence, we exposed 13 lungs to hypoxia, and during the hypoxic exposure we either decreased the inspired PCO2 (respiratory alkalosis, n = 8) or infused NaHCO3 (metabolic alkalosis, n = 5) to achieve a pH of 7.50-7.65. For the second sequence, we first decreased the inspired PCO2 (n = 9) or infused NaHCO3 (n = 11) to achieve a pH of 7.50-7.65 and then exposed the lungs to hypoxia. We found that hypoxic pulmonary vasoconstriction was reduced by either respiratory or metabolic alkalosis, when alkalosis was induced during hypoxia. When respiratory or metabolic alkalosis was induced before hypoxia, the magnitude of hypoxia-induced pulmonary vasoconstriction was the same as at the normal pH. We conclude that both metabolic and respiratory alkalosis reduce ongoing hypoxic pulmonary vasoconstriction in lungs of newborn rabbits. However, neither mode of alkalosis blunts pulmonary vasoconstriction in response to subsequent exposures to hypoxia.