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The effects of subfornical organ (SFO) lesions on salt and water intakes after sodium depletion were studied. Water and salt intakes were measured over 45 hr during a regimen that combined furosemide diuresis and access to low-sodium diet. Water was solely available for 23 hr after diuresis, and water and 0.3 M NaCl solution were available in choice for the next 22 hr. After diuresis, rats with SFO lesions drank significantly less water in 2 hr than controls but achieved equivalent water and sodium balances before salt access 20 hr later. After salt access, rats with SFO lesions drank significantly less saline and water in 2 hr than controls but had similar saline and water intakes over the next 20 hr. Thus, SFO lesions blunted acutely, but not chronically, saline and water intakes to sodium depletion, and the blunted intakes are not explainable by hydrational status.

Three experiments tested whether the subfornical organ (SFO) could be a site of action for the antidipsogenic effects of atrial natriuretic peptide (ANP) in rats. Pretreatment with 100, 230, or 500 pmol ANP in the SFO reduced drinking induced by 10 pmol angiotensin II in the SFO. Drinking in response to water deprivation was reduced by ANP in rats having cannulas in or near the SFO, but not in rats having cannulas distant from the SFO or in the ventricles. Finally, ANP had no effect on eating or drinking after food deprivation, suggesting that the rats in the other experiments were not acutely incapacitated. The SFO may mediate the central effects of ANP on drinking induced by angiotensin or in response to water deprivation and could play a similar role in the central effects of aNP on salt appetite, diuresis, vasopressin secretion, and blood pressure.