The effect of alpha and beta adrenergic blocking drugs upon the aversive threshold of rats

Abstract

An attempt was made to assay the analgesic potency of several adrenergic agents which included: reserpine (.62, 1.25, 2.50 mg/kg), phenoxybenzamine, an α-adrenergic blocking agent (5.0, 10.0, 20.0 mg/kg), and propranolol, a β-adrenergic blocking agent (1.0, 2.0, 3.0, 4.0, 6.0, 8.0 mg/kg) in the rat using the spatial preference technique. Only the β-adrenergic blocking agent, propranolol, consistently elevated the aversive threshold over a wide range of doses without affecting motor activity. Reserpine augmented the aversive threshold only under the highest dose tested, while phenoxybenzamine produced no reliable effects on pain sensitivity. These results were interpreted to suggest that the high dose of reserpine may have elevated the aversive threshold indirectly through its toxic effects on motor activity. Propranolol, on the other hand, may have produced a mild analgesia through the drug’s local anesthetic properties. It was suggested that reductions in central adrenergic tone via the administration of high doses of various drugs may elevate the aversive threshold indirectly by producing debilitating motor deficits.