Effects of various ganglionic blocking agents on blood pressure and on activity of pressor agents

Five structurally dissimilar ganglioplegic drugs used in the diagnosis and treatment of human hypertension were investigated in normotensive, trained dogs under conditions of profound, uniform, ganglionic blockade. Slow, continuous intravenous infusion did not lower the blood pressure of the conscious dog, and even induced a slight elevation. In a model experiment with tetraethylammonium chloride, the effect on the blood pressure depended on the rate of administration of the drug and on the state of consciousness of the animal. Rapid intravenous injection of a massive dose into an anesthetized dog, induced a profound fall of blood pressure. The pressor action of sympathomimetic amines, whether administered in a single dose or by continuous slow infusion, was greatly enhanced by the administration of ganglionic blocking agents, but the activity of other pressor agents, such as angiotensin and renin, was not enhanced under identical conditions. It is concluded that the potentiation of pressor agents cannot be ascribed to the blockade of compensatory, autonomic reflexes or to the considerable increase in heart rate which was observed in conscious dogs in all the experiments with ganglionic blocking agents.