THE ANTAGONISM OF THE EFFECTS OF l-3,4-DIHYDROXY- PHENYLALANINE ON SPINAL REFLEXES BY ADRENERGIC BLOCKING AGENTS

¹ Department of Pharmacology, University of Illinois College of Medicine, Chicago, Illinois

The alpha receptor blocking agents phenoxybenzamine, chlorpromazine and ethobutamoxane and the beta receptor blocking agent pronethalol were examined for their individual effects on spinal reflexes, and their ability to antagonize the actions of l-3,4-dihydroxphenylalanine (dopa). Phenoxybenzamine selectively increased the polysynaptic reflex area, ethobutamoxane depressed the monosynaptic spike height, pronethalol increased the dorsal root reflex and chlorpromazine had no significant action in the doses used. The different spectrum of activity shown by each antagonist suggests that these actions are unique to each compound and not the result of adrenergic blockade. All three alpha receptor blocking agents antagonized the dopa-induced increase in the monosynaptic reflex, decrease in the stimulus-response latency and depressed dorsal root reflex area. The direct effect of the agents on spinal reflexes made it difficult to establish their ability to antagonize the dopa-induced depression of polysynaptic reflexes. Pronethalol failed to show any significant antagonism to dopa. It is thus concluded that the action of dopa on the monosynaptic and dorsal root reflexes is mediated by the activation of alpha receptors.