The effects of dietary protein and converting enzyme inhibition (CEI) on chronic puromycin aminonucleoside nephropathy (PAN) were studied. PAN was induced with seven SQ injections of puromycin aminonucleoside 20 mg/kg over 10 weeks in male Sprague-Dawley rats. The rats were divided into a 22.5% protein diet group (Gr 1), a 6% protein diet group (Gr 2), and an enalapril-treated group on 22.5% protein diet (Gr 3). Group 4 animals served as age-matched controls. Both diets were isocaloric and had the same phosphorus content. Rats from groups 1, 2, and 4 were sacrificed at 12, 18 and 24 weeks. Five rats of group 3 were sacrificed at 12 weeks, and the others were divided in subgroups 3A (diet changed to 6% protein) and 3B (no changes); half of each subgroup was sacrificed at 18 and 24 weeks, respectively. Group 2 had significantly less proteinuria than group 1 at all times. Group 3 had the same proteinuria as group 1 until 12 weeks and then began to decrease. In group 3A proteinuria decreased to group 2 levels, while in group 3B the decrease was slower but still prominent. Early lesions of focal and segmental glomerular sclerosis/hyalinosis (FSH) were present in groups 1, 2, 3 at 12 weeks (16 +/- 1.2%, 15 +/- 1.3%, 7 +/- 1.3%, respectively, versus 1.3 +/- 0.4% in controls), but by 18 weeks a reversal in FSH was seen in groups 2 and 3A/B (3 +/- 1.6%, 2 +/- 0.4%, and 3 +/- 0.9%, respectively, vs. 14 +/- 1.5% in group 1).(ABSTRACT TRUNCATED AT 250 WORDS)