Separation of captopril effects on salt and water intake by subfornical organ lesions

Several experiments tested whether the subfornical organ (SFO) is necessary for water or NaCl intake arising from angiotensin-converting enzyme (CE) blockade with captopril (CAP) in the drinking fluids (0.1 mg/ml). Peripheral CAP was given to rats acutely following 24-h water deprivation or chronically over several days, either with water alone available for drinking or with 0.3 M NaCl in choice with water. Control rats drank more water, and NaCl when it was available, during CAP treatment, whereas rats with SFO damage increased NaCl intake only. CAP decreased urinary volume (UV) and increased urinary potassium excretion (UKV) during rehydration with only water available and increased urinary sodium excretion (UNaV) with NaCl present. Regardless of CAP treatment, rats with SFO damage had increased electrolyte concentrations and excretions during rehydration with only water available and increased UK with NaCl present, compared with controls. Oral CAP did not have an aversive taste at the dose used here. We conclude that the SFO is necessary for CAP-enhanced water, but not NaCl, intake and suggest that different neurological mechanisms control ingestion of each fluid during CAP.