Effects of alpha(1)-adrenoceptors and muscarinic cholinoceptors on water intake in rats

The present study investigated the effects of alpha(1)-adrenoceptors and muscarinic cholinoceptors on water intake in adult male rats. Intracerebroventricular (i.c.v.) injections were carried out in all experiments after 24-h deprivation of water. After deprivation, the volume of consumed water was measured for 1 h. Administration of pilocarpine, a muscarinic cholinoceptor agonist (0.5-1 microg/rat), and prazosin, the alpha(1)-adrenoceptors antagonist (2 microg/rat), increased, while scopolamine, a muscarinic cholinoceptor antagonist (5-10 microg/rat), and phenylephrine, an alpha(1)-adrenoceptor agonist (30 microg/rat), decreased water intake in rats. The activation of muscarinic cholinoceptors by pilocarpine attenuated the inhibitory effect induced by phenylephrine. Blockade of muscarinic cholinoceptors did not change the phenylephrine-induced response. Pretreatment with prazosin decreased the pilocarpine-induced response. However, pharmacological blockade of muscarinic cholinoceptors by scopolamine decreased the prazosin-induced effect on water intake. It is concluded that muscarinic cholinoceptors and alpha(1)-adrenoceptors may interact on water intake.