Circumventricular organs and ANG II-induced salt appetite: blood pressure and connectivity

A lesion of the subfornical organ (SFO) may reduce sodium depletion-induced salt appetite, which is largely dependent on ANG II, and yet ANG II infusi ons directly into SFO do not provoke salt appetite. Two experiments were de signed to address this apparent contradiction. In experiment 1 sustained in fusions of ANG II into SFO did not produce a sustained elevation of blood p ressure, and neither a reduction of blood pressure alone with minoxidil and captopril nor a reduction of both blood pressure and volume with furosemid e and captopril enhanced salt appetite. Infusions of ANG II in the organum vasculosum laminae terminalis (OVLT) did evoke salt appetite without raisin g blood pressure. In experiment 2 knife cuts of the afferent and efferent f ibers of the rostroventral pole of the SFO abolished water intake during an infusion of ANG II into the femoral vein but failed to reduce salt appetit e during an infusion of ANG II into the OVLT. We conclude that 1) hypertens ion does not account for the failure of infusions of ANG II in the SFO to g enerate salt appetite and 2) the OVLT does not depend on its connectivity w ith the SFO to generate salt appetite during ANG II infusions.