Hyperoxia blunts acute hypoxia- and PGF2alpha-induced pulmonary vasoconstriction in chronically hypoxic rats

We investigated the influence of oxygenation of in vitro lung preparation on the pulmonary vascular reactivity. Small pulmonary vessels isolated from adult male Wistar rats exposed for 4 days to hypoxia (F(iO2) = 0.1, group CH) were compared with those of normoxic controls (group N). The bath in the chamber of small vessel myograph was saturated with gas mixture containing either 21% or 95% of O(2) with 5% CO(2) and we measured the reactions of vessels to acute hypoxic challenge with 0% O(2) or to PGF(2alpha). We did not observe any difference of the contractile responses between both groups when the normoxic conditions were set in the bath. When the bath oxygenation was increased to 95% O(2), the contractions induced by hypoxic challenge and PGF(2alpha) decreased in chronically hypoxic rats and did not change in normoxic controls. We hypothesize that reduced reactivity of vessels from hypoxic rats in hyperoxia results from the effect of chronic hypoxia on Ca(2+) signaling in the vascular smooth muscle, which is modulated by increased free radical production during the exposure to chronic hypoxia and further hyperoxia.