CLONIDINE AND PHENYLEPHRINE INJECTED INTO THE LATERAL PREOPTIC AREA REDUCE WATER-INTAKE IN DEHYDRATED RATS

In the present study, we investigated the effect of phenylephrine and clonidine (alpha1- and alpha2-adrenoceptor agonists, respectively) inj ected into the lateral preoptic area (LPOA) on the water intake induce d by water deprivation in rats. In addition, the effects of prior inje ctions of prazosin and yohimbine (alpha1- and alpha2-adrenoceptor anta gonists, respectively) into the LPOA on the antidipsogenic action of p henylephrine and clonidine were investigated. After 30 h of water depr ivation, the water intake of rats in a control experiment (saline inje ction) was 10.5 +/- 0.8 ml/h. Injection of clonidine (5, 10, 20, and 4 0 nmol) into the LPOA reduced water intake to 6.3 +/- 0.9, 4.9 +/- 0.8 , 3.6 +/- 1.0, and 2.2 +/- 0.7 ml/h, respectively. Similar reductions occurred after injection of 80 and 160 nmol phenylephrine into the LPO A (6.2 +/- 1.6 and 4.8 +/- 1.3 ml/h, respectively). Pretreatment with prazosin (40 nmol) abolished the antidipsogenic action of an 80-nmol d ose of phenylephrine (11.3 +/- 1.1 ml/h) and reduced the effect of a 2 0-nmol dose of clonidine (7.4 +/- 1.4 ml/h). Yohimbine (20, 40, and 80 nmol), previously injected, produced no significant changes in the ef fects of either phenylephrine or clonidine. The present results show t hat phenylephrine and clonidine injected into the LPOA induce an antid ipsogenic effect in water-deprived rat. They also suggest an involveme nt of alpha1-adrenoceptors in this effect. A possible participation of imidazole receptors in the effect of clonidine should also be taken i nto account.