Role of brain acetylcholine in vasopressin release during osmotic stimulation and hemorrhage

There is considerable evidence to suggest that there is a cholinergic link in the neural control of vasopressin release, but the precise role for this link has not been adequately demonstrated in the intact animal. We have, therefore, examined in conscious unrestrained rats the effects of central cholinergic blockade on the stimulation of vasopressin release by increased plasma osmotality (iv infusion of 2.5 M NaCl at 0.1 mg/kg body weight.min for 30 min) and by decreased blood volume (2 successive hemorrhages of 10% of blood volume each). The vasopressin responses to these stimuli were unaffected by either intracerebroventricular (icv) atropine (10 micrograms; muscarinic blockade) or icv hexamethonium (10 micrograms; nicotinic blockade) in doses which block the vasopressin responses to icv cholinergic agonists. The implications of these findings are discussed.