VENTROMEDIAL HYPOTHALAMUS LESIONS INCREASE THE DIPSOGENIC RESPONSES AND REDUCE THE PRESSOR-RESPONSES TO MEDIAN PREOPTIC AREA ACTIVATION

In this study, we investigated the participation of adrenergic recepto rs of the median preoptic area (MnPO) and the participation of ventrom edial hypothalamus (VMH) in angiotensin II- (ANG II)-induced water int ake and presser responses. Male rats with sham or electrolytic VMH les ions and a stainless steel cannula implanted into the MnPO were used. Noradrenaline, clonidine (an alpha(2)-adrenergic receptor agonist), or phenylephrine (an alpha(1)-adrenergic receptor agonist) injected into the MnPO of sham-lesioned rats reduced water ingestion induced by ANG II injected into the same area. In VMH-lesioned rats ANG II-induced w ater intake increased with a previous injection of noradrenaline, phen ylephrine, or isoproterenol. The presser response induced by ANG II in jected into the MnPO was reduced in VMH-lesioned rats, whereas the pre sser response induced by clonidine was abolished. Previous treatment w ith noradrenaline and phenylephrine into the MnPO of sham-lesioned rat s produced a presser response, and a hypotensive response was obtained with the previous administration of noradrenaline, phenylephrine or i soproterenol into the MnPO of VMH-lesioned rats. These results show th at VMH is essential for the dipsogenic and presser responses induced b y adrenergic and angiotensinergic activation of the MnPO in rats. (C) 1997 Elsevier Science Inc.