Thromboxane-induced pulmonary vasoconstriction: Involvement of calcium

Infusion of tert-butyl hydroperoxide (t-bu-OOH) or arachidonic acid into rabbit pulmonary arteries stimulated thromboxane B₂ (TxB₂) production and caused pulmonary vasoconstriction. Both phenomena were blocked by cyclooxygenase inhibitors or a thromboxane synthase inhibitor. The increase in pulmonary arterial pressure caused by either t-bu-OOH or arachidonic acid infusion correlated with the concentration of TxB₂ in the effluent perfusate. The concentration of TxB₂ in the effluent perfusate, however, was always 10-fold greater after arachidonic acid infusion. In the rabbit pulmonary vascular bed lipoxygenase products did not appear involved in the vasoactive response to t-bu-OOH or exogenous arachidonic acid infusion. Calcium entry blockers or a calcium-free perfusate prevented the thromboxane-induced pulmonary vasoconstriction. Calmodulin inhibitors also blocked the pulmonary vasoconstriction induced by t-bu-OOH without affecting the production of TxB₂ or prostacyclin. These results suggest that thromboxane causes pulmonary vasoconstriction by increasing cytosol calcium concentration.