Alpha-adrenergic control of ANG II-induced drinking in the rat median preoptic nucleus

The present study was carried out to investigate the contribution of angiotensinergic and catecholaminergic systems in the median preoptic nucleus (MnPO) to the drinking response elicited by activation of the subfornical organ (SFO) following injections of angiotensin II (ANG II) in the awake unrestrained rat. Microinjection of ANG II into the SFO caused the drinking response. The water intake caused by ANG II injected into the SFO was significantly enhanced by previous injections of phenylephrine, an alpha-adrenoceptor agonist, but not by isoprenaline, a beta-adrenoceptor agonist. Previous injections of either saralasin, a specific ANG II antagonist, or phentolamine, an alpha-adrenoceptor antagonist, into the MnPO significantly attenuated the water intake caused by the ANG II injection into the SFO. Similar injections of timolol, a beta-adrenoceptor antagonist, or the vehicle into the MnPO had no significant effect on the drinking response. These results show the involvement of both angiotensinergic and alpha-adrenergic systems in the MnPO in the drinking response induced by ANG II acting at the SFO, and imply that the alpha-adrenergic system may serve to enhance the neural inputs including the angiotensinergic inputs from the SFO, thereby causing increased dipsogenic response.