Effects of subfornical organ lesions on acutely induced thirst and salt appetite

We examined the role of the subfornical organ (SFO) in stimulating thirst a nd salt appetite using two procedures that initiate water and sodium ingest ion within 1-2 h of extracellular fluid depletion. The first procedure used injections of a diuretic (furosemide, 10 mg/kg sc) and a vasodilator (mino xidil, 1-3 mg/kg ia) to produce hypotension concurrently with hypovolemia. The resulting water and sodium intakes were inhibited by intravenous admini stration of ANG II receptor antagonist (sarthran, 8 mu g.kg(-1).min(-1)) or angiotensin-converting enzyme inhibitor (captopril, 2.5 mg/h). The second procedure used injections of furosemide (10 mg/kg sc) and a low dose of cap topril (5 mg/kg sc) to initiate water and sodium ingestion upon formation o f ANG II in the brain. Electrolytic lesions of the SFO greatly reduced the water intakes, and nearly abolished the sodium intakes, produced by these r elatively acute treatments. These results contrast with earlier findings sh owing little effect of SFO lesions on sodium ingestion after longer-term ex tracellular fluid depletion.