SELECTIVE REDUCTION IN NEUROGENICALLY INDUCED CONSTRICTION BY PHENOXYBENZAMINE

¹ Department of Pharmacology, Basic Medical science Building, University of Michigan, Ann Arbor, Michigan

The capacity of alpha and beta adrenergic blocking agents to modify neurogenically and humorally induced constriction has been tested in the perfused extremity of the dog. Our findings do not support the classic view that the response produced by norepinephrine is more easily blocked than the response produced by nerve stimulation. Phenoxybenzamine reduced the vasoconstnictor response produced by pre-or postganglionic sympathetic nerve stimulation significantly more than the constrictor response produced by intra-arterially injected norepinephrine. Phentolamine blocked both types of induced constriction equally. The preferential reduction in the neurogenic response by phenoxybenzamine does not appear to result from the neurogenic release of a substance with more beta adrenergic stimulating actions than norepinephrine because 1) propranolol caused an equivalent increase in norepinephrine and neurogenically induced constriction, and 2) phenoxybenzamine still produced a greater reduction in the neurogenic constriction after pretreatment with propranolol.