CHOLINE ADMINISTRATION REVERSES HYPOTENSION IN SPINAL-CORD TRANSECTEDRATS - THE INVOLVEMENT OF VASOPRESSIN

Intracerebroventricular (i.c.v.) choline (50-150 mu g) increased blood pressure and decreased heart rate in spinal cord transected, hypotens ive rats. Choline administered intraperitoneally (60 mg/kg), also, inc reased blood pressure, but to a lesser extent. The presser response to i.c.v. choline was associated with an increase in plasma vasopressin. Mecamylamine pretreatment (50 mu g; i.c.v.) blocked the presser, brad ycardic and vasopressin responses to choline (150 mu g). Atropine pret reatment (10 mu g; i.c.v.) abolished the bradycardia but failed to alt er presser and vasopressin responses. Hemicholinium-3 [HC-3 (20 mu g; i.c.v.)] pretreatment attenuated both bradycardia and presser response s to choline. The vasopressin V1 receptor antagonist, rcapto-beta,beta -cyclopenta-methylenepropionyl(1), O-Me-Tyr(2), Arg(8))-vasopressin (1 0 mu g/kg) administered intravenously 5 min after choline abolished th e presser response and attenuated the bradycardia-induced by choline. These data show that choline restores hypotension effectively by activ ating central nicotinic receptors via presynaptic mechanisms, in spina l shock. Choline-induced bradycardia is mediated by central nicotinic and muscarinic receptors. Increase in plasma vasopressin is involved i n cardiovascular effects of choline.