INCREASED SYMPATHETIC VASOCONSTRICTOR TONE IN DOGS TREATED CHRONICALLY WITH MECAMYLAMINE

¹ Instituto Miles de Terapéutica Experimental, México, D.F., México

Blood pressure changes produced by drug-induced blockade of adrenergic activity were studied as a means of assessing sympathetic vasoconstrictor tone in normotensive dogs and in dogs made hypertensive by either bilateral constriction of the renal arteries or by chronic mecamylamine administration. In experiments on unanesthetized dogs, the mecamylamine hypertensive animals were more sensitive to the depressor effects of the blocking agents than dogs from the other two groups, and renal hypertensive animals were more sensitive than the normotensive dogs. In experiments involving pentobarbital anesthesia, differences in reactivity to zolertine among the three types of dog were minimal. This coincided with increases in blood pressure produced by the barbiturate in the normotensive and renal hypertensive dogs but not in the mecamylamine hypertensive animal. The sensitivity of the anesthetized animals to the pressor effect of norepinephrine was also similar among the three groups. The results were interpreted as indicating varying degrees of sympathetic vasoconstrictor tone in unanesthetized animals of the diverse types and as supporting the hypothesis that increased vasoconstrictor tone is a component of the sustained hypertension which develops in dogs after the prolonged administration of mecamylamine.