Thirst and sodium appetite after colloid treatment in rats: role of the renin-angiotensin-aldosterone system.

Recent experiments indicated that rats usually develop sodium appetite 5 hr after subcutaneous injection of polyethylene glycol (PEG) solution. However, sodium appetite appeared within 30 to 60 min if the rats had been maintained on sodium-deficient diet instead of Purina chow for 2-4 days previously. Elevated levels of aldosterone paralleled the appearance of NaCl consumption in both circumstances. In the present experiments, sodium appetite was no longer potentiated by pretreatment maintenance on sodium-deficient diet when the hypersecretion of aldosterone after PEG administration was prevented by prior hypophysectomy. Conversely, sodium appetite was enhanced in PEG-treated rats when angiotensin II (AII) was produced in unusually large amounts in the brain, owing to the systemic administration of captopril. This latter effect occurred even when drinking water was withheld and plasma sodium concentrations were markedly elevated. These and other findings raise the possibility that the normal secretion of aldosterone in rats after PEG treatment might permit physiological amounts of AII to be effective in stimulating sodium appetite. Such actions would complement the accepted physiological role of the renin-angiotension-aldosterone system in the maintenance of blood pressure and sodium balance.