INTRACEREBROVENTRICULAR CHOLINE REVERSES HYPOTENSION INDUCED BY ACUTECHEMICAL SYMPATHECTOMY

1 The effect of centrally administered choline on blood pressure was i nvestigated in rats made hypotensive by chemical sympathectomy. Chemic al sympathectomy was produced by intravenous (i.v.) injection of 50 mg kg(-1) of 6-hydroxydopamine (6-OHDA). Intracerebroventricular (i.c.v. ) administration of choline (50-150 mu g) 2 h after 6-OHDA treatment i ncreased blood pressure and reversed the hypotension in a dose-depende nt mariner without affecting heart rate. The presser response was asso ciated with an increase in plasma vasopressin levels. 2 Pretreatment o f rats with the nicotinic receptor antagonist, mecamylamine (50 mu g, i.c.v.), but not the muscarinic receptor antagonist atropine (10 mu g, i.c.v.), blocked both the presser and vasopressin responses to cholin e (150 mu g). Pretreatment of rats with hemicholinium-3 (HC-3), a high affinity choline uptake inhibitor, greatly attenuated the presser res ponse to i.c.v. choline (150 mu g). 3 The vasopressin V1 receptor anta gonist, mercapto-beta,beta-cyclopentamethylenepropionyl-O- Me-Try,Arg) -vasopressin (10 mu g kg(-1); i.v.), given 5 min after i.c.v. choline, decreased the blood pressure but failed to return it to the pre-choli ne levels. Prazosine (0.5 mg kg(-1); i.p.), an antagonist of a-adrenoc eptors, also decreased blood pressure. Administration of both antagoni sts together eliminated the presser response to choline, and the blood pressure was reduced further to below the pre-choline levels. 4 It is concluded that i.c.v. choline can increase blood pressure in rats mad e hypotensive by acute chemical sympathectomy through the activation o f central nicotinic receptors by presynaptic mechanisms. An elevation in plasma levels of both vasopressin and catecholamines (possibly rele ased from the adrenal medulla) is involved in the pressor response to choline.