The effect of captopril or enalaprilic acid on the Na appetite of Na-deplete rats.

1. The converting enzyme inhibitors, captopril (SQ14 225, Squibb) or enalaprilic acid (MK 422, Merck Sharp and Dohme), were used to evaluate the role of angiotensin II in sodium (Na) appetite of Na-deplete rats given a choice of water and 0.5 mol/l NaCl to drink. Also, the effect of these drugs on taste was evaluated in water-deprived Na-replete rats and in Na-deplete rats given a choice of NaCl, sucrose and water. 2. Intraperitoneal (i.p.) injection of furosemide (20 mg/kg) increased urinary Na loss by 1.3-1.4 mmol and subsequent Na intake by 1.5-1.8 mmol. This increase in Na intake was abolished by a high dose of captopril (50 mg/kg, i.p.) or enalaprilic acid (80 mg/kg, i.p.), but was enhanced by a low dose of captopril (50 micrograms/kg, i.p.). 3. There was no clear evidence that either captopril or enalapril affected taste for NaCl, sucrose or water in water-deprived Na-replete rats. However, the high dose of captopril or enalapril decreased the intake of NaCl and sucrose in Na-deplete rats. 4. Thus, while the results are consistent with the possibility that angiotensin II is involved in Na appetite induced by Na depletion and that the difference between the high and low doses of converting enzyme inhibitors on Na appetite may be related to their relative effectiveness in blocking angiotensin I conversion at central sites, the observation that sucrose intake is decreased by high dose converting enzyme inhibitor in Na-deplete rats suggests that other actions of the converting enzyme inhibitors may be involved.