Hypothalamic angiotensin release in response to AII or glutamic acid stimulation of the SFO in rats

Recent evidence from our laboratory suggests that angiotensin II (AII) is synthesized, stored within cells in the paraventricular nucleus (PVN) of the hypothalamus, and upon appropriate stimulation, released and rapidly converted to angiotensin III (AIII). The present investigation extends these observations by first employing a retrograde tracer to confirm a direct connection from the subfornical organ (SFO) to the PVN, and then showing that microinfusion of AII or glutamic acid into the SFO provokes release of endogenous angiotensin within the PVN. Potentially it is this release that contributes to the elevations in blood pressure and drinking that have been reported to occur with electrical and chemical stimulation of the SFO. These results represent the first evidence of releasable angiotensin provoked by the chemical activation of a neural pathway that has been histochemically demonstrated to link the SFO with the PVN and brain stem structures concerned with cardiovascular functioning.