Pentobarbital augments pulmonary vasoconstrictor response to cyclooxygenase inhibition

We utilized multipoint pulmonary vascular pressure-flow (P/Q̇) plots to investigate the effects of pentobarbital sodium anesthesia on regulation of the pulmonary circulation by endogenous metabolites of the cyclooxygenase pathway. Our specific objective was to characterize the effects of two chemically dissimilar inhibitors of the cyclooxygenase pathway, indomethacin and sodium meclofenamate, on the pulmonary vascular P/Q̇ relationship measured in conscious and pentobarbital-anesthetized dogs. P/Q̇ plots were generated by graded constriction of the thoracic inferior vena cava, which produced stepwise decreases in Q̇. Controlled ventilation during pentobarbital anesthesia (30 mg/kg iv) allowed the matching of systemic arterial and mixed venous blood gases to conscious values. Pentobarbital had no net effect on the base-line P/Q̇ relationship compared with that measured in conscious dogs. Cyclooxygenase pathway inhibition with either indomethacin (5 mg/kg iv) or meclofenamate (2.5 mg/kg iv) resulted in active, flow-independent pulmonary vasoconstriction (P < 0.01) in both conscious and pentobarbital-anesthetized dogs. However, the magnitude of the pulmonary vasoconstrictor response to indomethacin was increased (P < 0.05) over a broad range of Q̇, and the pulmonary vasoconstrictor response to meclofenamate was increased (P < 0.05) over the entire range of Q̇ in pentobarbital-anesthetized compared with conscious dogs. Thus regulation of the base-line pulmonary vascular P/Q̇ relationship by endogenous metabolites of the cyclooxygenase pathway in conscious dogs is altered during pentobarbital anesthesia.