RESTORATION OF BLOOD-PRESSURE BY CHOLINE TREATMENT IN RATS MADE HYPOTENSIVE BY HEMORRHAGE

1 Intracerebroventricular (i.c.v.) injection of choline (25 - 150 mu g ) increased blood pressure in rats made acutely hypotensive by haemorr hage. Intraperitoneal administration of choline (60 mg kg(-1)) also in creased blood pressure, but to a lesser extent. Following i.c.v. injec tion of 25 mu g or 50 mu g of choline, heart rate did not change, whil e 100 mu g or 150 pg i.c.v. choline produced a slight and short lastin g bradycardia. Choline (150 mu g) failed to alter the circulating resi dual volume of blood in haemorrhaged rats. 2 The presser response to i .c.v. choline (50 mu g) in haemorrhaged rats was abolished by pretreat ment with mecamylamine (50 mu g, i.c.v.) but not atropine (10 mu g, i. c.v.). The presser response to choline was blocked by pretreatment wit h hemicholinium-3 (20 mu g, i.c.v.). 3 The presser response to i.c.v. choline (150 mu g) was associated with a several fold increase in plas ma levels of vasopressin and adrenaline but not of noradrenaline and p lasma renin. 4 The presser response to i.c.v. choline (150 mu g) was n ot altered by bilateral adrenalectomy, but was attenuated by systemic administration of either phentolamine (10 mg kg(-1)) or the vasopressi n antagonist rcapto-beta,beta-cyclopenta-methylenepropionyl(1), O-Me-T yr(2),Arg(8)]-vasopressin (10 mu g kg(-1)). 5 It is concluded that the precursor of acetylcholine, choline, can increase and restore blood p ressure in acutely haemorrhaged rats by increasing central cholinergic neurotransmission. Nicotinic receptor activation and an increase in p lasma vasopressin and adrenaline level appear to be involved in this e ffect of choline.