THE EFFECT OF NOREPINEPHRINE ON CARDIAC OUTPUT, ARTERIAL BLOOD PRESSURE, AND HEART RATE IN DOGS TREATED WITH CHLOROTHIAZIDE*†

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Abstract
Cardiovascular responses to graded doses of norepinephrine were measured in 12 dogs anesthetized lightly with thiopental and decamethonium. Six had been treated with chlorothiazide, 25 mg/kg/day, for 7 days-, 6 were untreated. All had received water ad libitum and the same diet for 7 days. Norepinephrine was infused intravenously at rates of 0.1, 0.2 and 0.4 jig/kg/minute. Each dose was repeated in each animal. The order of infusion was randomized in all the dogs using a 6 x 6 Latin Square. Observations were made immediately before and after 2 1/2 minutes of norepinephrine infusion. Cardiac output did not change appreciably, but arterial pressure and peripheral resistance increased significantly with increasing doses of norepinephrine in untreated dogs. Treated dogs had significant increases in cardiac output but only slight increases in peripheral resistance. The changes in arterial pressure were about the same in the two groups, but the reduction in heart rate was less in treated dogs.