1. We have investigated the effects of the non-renin-mediated actions of angiotensin converting enzyme inhibitors on the progression of chronic renal failure accelerated by hypertension. For this purpose, we studied the effects of captopril (a thiol-containing angiotensin converting enzyme inhibitor), enalapril (an angiotensin converting enzyme inhibitor without a thiol group) and cysteine (a thiol-containing amino acid which has no angiotensin converting enzyme-inhibitory action) in adriamycin-treated rats with deoxycorticosterone acetate-salt hypertension, in which the renin-angiotensin system was suppressed.

2. There were no significant differences in blood pressure between these groups and the control group [adriamycin-treated group with deoxycorticosterone acetate-salt loading, 206 ± 7 mmHg (27.4 ± 0.9 kPa) at week 10].

3. Massive proteinuria occurred in all groups. At the end of the experiment (at week 10), urinary protein excretion was significantly reduced in the captopril and cysteine groups compared with the control group. No manifest improvements appeared in the enalapril group.

4. Levels of serum creatinine and blood urea nitrogen increased progressively. At week 10, the increases in the serum levels of creatinine were less in the captopril (87 ± 16 mmol/l) and cysteine (80 ± 19 mmol/l) groups than in the control group (124 ± 27 mmol/l) (P < 0.01). No marked differences were found between the control and enalapril groups.

5. Captopril and cysteine caused more than a threefold reduction in the focal glomerulosclerosis score when compared with that in the control group, but enalapril did not decrease the score. The extent of tubulo-interstitial change was parallel with the focal glomerulosclerosis score.

6. We conclude that the thiol group is possibly involved in the mechanism of the beneficial effects of some angiotensin converting enzyme inhibitors on the progression of chronic renal failure exacerbated by hypertension.

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