Pulmonary vasodilation by ketamine is mediated in part by L-type calcium channels

We studied the effects of ketamine in the isolated rat lung under conditions of increased pulmonary arterial pressure using the thromboxane A(2) mimic, U46619, and in response to ventilatory hypoxia. Ketamine caused dose-dependent vasodilation, and possible mechanisms were evaluated using verapamil, meclofenamate, N-omega-L-nitro-L-arginine benzyl ester tan inhibitor of nitric oxide synthase), and U-38883A tan ATP-sensitive potassium channel antagonist) in the isolated blood-perfused rat lung. Under increased tone conditions, N-omega-L-nitro-L-arginine benzyl ester, meclofenamate, and U-38883A had no significant effect in attenuating ketamine-induced vasodilator responses. In a final series of experiments, verapamil significantly attenuated ketamine-induced vasodilator responses. These data suggest that ketamine has significant vasodilator activity in the pulmonary vascular bed of the rat, which seems to be mediated by an L-type calcium channel-sensitive pathway. These responses are not mediated or modulated by the release of nitric oxide, the activation of K(+)ATP channels, or the release of vasodilator cyclooxygenase products. Implications: In this study, we examined the mechanism of the vasodilator effects of ketamine in the blood-perfused rat lung. The results of the present study suggest that ketamine-induced vasodilator responses are mediated by an L-type calcium channel-sensitive pathway.