Release by hypoxia of a soluble vasoconstrictor from rabbit small pulmonary arteries

Soluble pulmonary vasoconstrictors released in response to hypoxia have been reported in pig and rat preparations, but not in rabbit preparations. We used myography to evaluate the contribution of a soluble factor to constriction in rabbit small pulmonary arteries (external diameter 300–475 μm) exposed to 45 min hypoxia (Po2=9 mm Hg). Hypoxia produced gradually intensifying constriction. Return to euoxia (Po2=145 mm Hg) for 30 min relaxed only approximately 30% of the constriction, whereas elution of the myograph bath yielded full relaxation. Reapplication of the eluent gradually restored the constriction to its pre-elution level over a 30-min period. In this closed system, a soluble factor contributes substantially to hypoxic pulmonary vasoconstriction.