Central cholinergic control of vasopressin release in conscious rats

Intracerebroventricular (icv) administration of carbachol into conscious rats evoked a substantial increase in vasopressin secretion and blood pressure in a dose-dependent manner. These effects were blocked by pretreatment with the muscarinic blocker, atropine (10 micrograms icv), but not by the nicotinic blocker, hexamethonium (10 micrograms icv). Hexamethonium did, however, block the increase in blood pressure, the decrease in heart rate, and the very small elevation in the plasma vasopressin concentration induced by nicotine (10 micrograms icv). These results indicate that stimulation of either central nicotinic or muscarinic receptors can affect the cardiovascular system and suggest that the cholinergic stimulation of vasopressin secretion may involve primarily muscarinic receptors in the conscious rat.