Effects of intracerebroventricular injected choline on cardiovascular functions and sympathoadrenal activity

Intracerebroventricular (i.c.v.) injection of choline (50-150 micrograms) increased blood pressure (SP) and decreased heart rate (HR) in freely moving rats. Intracerebroventricular pretreatment of rats with mecamylamine (50 micrograms) blocked the reduction in HR and reduced the increase in SP induced by i.c.v. choline (150 micrograms). Central muscarinic blockade with atropine (10 micrograms, i.c.v.) reduced the pressor response to i.c.v. choline (150 micrograms) by about 70%, without influencing the decrease in HR. The decrease in HR induced by i.c.v. choline was prevented by intraarterial (i.a.) treatment of atropine methylnitrate (2 mg/kg). Intracerebroventricular choline (150 micrograms) produced a fivefold increase in catecholamine concentrations in adrenal venous plasma. Bilateral adrenalectomy reduced, but did not block, choline's effect on SP. Intracerebroventricular choline (150 micrograms) showed an ability to increase and restore SP in rats subjected to spinal cord transection or pretreatment with hexamethonium (15 mg/kg, i.a.) or with phentolamine (10 mg/kg, i.a.). Intracerebroventricular choline (150 micrograms) increased plasma vasopressin (VP) levels from 2.2 +/- 0.4 to 25.6 +/- 2.5 pg/ml. Pretreatment of rats with a VP antagonist reduced the pressor response to i.c.v. choline. It is concluded that (a) the reduction in HR results from a central nicotinic receptor-mediated increase in vagal tone, (b) the increase in SP appears to be due to activation of both nicotinic and muscarinic central cholinergic receptors, and that (c) the central activation of the adrenal medulla and the increase in plasma levels of VP are involved in the pressor response to i.c.v. choline.