Angiotensinergic and noradrenergic mechanisms in the hypothalamic paraventricular nucleus participate in the drinking response induced by activation of the subfornical organ in rats.

The present study was done to investigate the contribution of the hypothalamic paraventricular nucleus (PVN) to the drinking response caused by activation of the subfornical organ (SFO) following angiotensin II (ANG II) injections in the awake rat. Microinjection of ANG II into the SFO elicited the drinking response. Previous injections of either saralasin, an ANG II antagonist, or phentolamine, an alpha-adrenoceptor antagonist, bilaterally into the PVN resulted in the significant attenuation of the drinking response to ANG II. Similar injections of any of the beta-adrenoceptor antagonist timolol, the muscarinic antagonist atropine, or saline vehicle into the PVN had no significant effect on the drinking response. In an attempt to clarify the neural mechanisms in the PVN involved in the drinking response to ANG II injected into the SFO, the effect of microinjection of ANG II into the SFO on noradrenaline (NA) release in the PVN was examined using intracerebral microdialysis techniques. The injection of the ANG II, but not saline vehicle, significantly enhanced the NA release in the region of the PVN. These results indicate the involvement of both the angiotensinergic and alpha-adrenergic systems in the PVN in the drinking response caused by angiotensinergic activation of the SFO, and imply that the angiotensinergic projections from the SFO to the PVN may serve to increase NA release which results in mediating water intake.