Action of pilocarpine on the rat blood pressure
Singh, G.
Indian Journal of Physiology and Pharmacology 19(4): 227-228
1975
ISSN/ISBN: 0019-5499 PMID: 1223004 Document Number: 86450
The mechanism of action of pilocarpine on rat blood pressure was studied. Pilocarpine nitrate (0.1 mg/kg) decreased, then increased blood pressure. Injection of 0.1 mg/kg of pilocarpine into 6 rats 10-30 min after haxamethonium (10 mg/kg) left the pilocarpine response unaffected. Hemicholinium (4 mg/kg) converted pilocarpine's biphasic action into a pressor response by blocking the depressor phase. Reserpine pretreatment (2.5 mg/kg i.p. for 2 days) abolished the pressor phase. Depressor response to pilocarpine in reserpine-pretreated rats was blocked by hemicholinium. Bretylium tosylate, an adrenergic neuron blocking agent, given 10 min before pilocarpine blocked the pressor phase of pilocarpine action. Pressor and depressor phases of the pilocarpine response were blocked by phenoxybenzamine (10 mg/kg) and atropine (1 mg/kg in divided doses)(Atropine was injected 10 min and phenoxybenzamine injected 30 min before pilocarpine). Presumably the depressor response to pilocarpine is due acetylcholine release, as it is blocked by atropine and by hemicholinium, an inhibitor of acetylcholine synthesis. Blockade of depressor phase by phenoxybenzamine may be due to a lowering of basal blood pressure or to a specific action. Pilocarpine's pressor action in the rat is presumably due to catecholamines liberation, as it is blocked by phenoxybenzamine, bretylium and reserpine. Atropine blocks the pressor response to pilocarpine in the rat. In the rat pilocarpine may be releasing catecholamines by acting on atropine-sensitive receptors on the sympathetic ganglion and adrenal medulla.