The actions of ketamine on vascular smooth muscle.

The responses of rabbit aortic strips superfused with noradrenaline, adrenaline and 5-HT were studied alone and in combination with ketamine (50 mug/ml). Ketamine caused a slight depression of the isolated aorta but potentiated responses to adrenaline but not to noradrenaline or 5-hydroxytryptamine. Ketamine did not potentiate aortic strips contracted to a stable level by pyrogallol and adrenaline. Experiments carried out with COMT from homogenates of rat liver showed that, in contrast to pyrogallol (10(-5) M), ketamine (10(-3) M) did not inhibit the enzyme. Other experiments with rabbits given 6-hydroxydopamine showed that aortas of these rabbits responded in a similar manner to controls when treated with ketamine and catecholamines. Results obtained with aortas contracted by adrenaline and noradrenaline with ketamine present, followed by oil immersion, showed that ketamine prolonged greatly the relaxation induced by adrenaline and to a lesser extent the relaxation induced by noradrenaline. The results of these studies indicate that ketamine prevented catecholamines from reaching the intracellular site of COMT. In this respect, ketamine can be termed an inhibitor of uptake site 2. If this hypothesis is valid then the action of ketamine on vascular tissue might explain the cardiovascular effects of the drug in man and experimental animals.