Investigation of some effects of levamisole on dog blood pressure

The effects of levamisole were investigated on the blood pressure of anaesthetized dog. Levamisole (0.5 to 4.0 mg/kg) elicited a biphasic effect, an initial brief depressor response followed by a pressor response. The pressor response was dose-related and was blocked by phenoxybenzamine. The residual depressor response was blocked by propranolol. Repeated administration of a high dose of levamisole produced tachyphylaxis. The pressor response to levamisole was not modified by either reserpinization, acute bilateral adrenalectomy or pretreatment with cocaine, whereas pretreatment with dexamethasone, nialamide or pyroaallol shifted the dose-response curve to the right. Levamisole potentiated the pressor responses to noradrenaline, angiotensin and acetylcholine. The effects of levamisole are ascribed to inhibition of monoamine oxidase, catechol-O-methyl transferase, catecholamine uptake2 mechanism and cholinesterase.