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Hyperlipidemic Imai rats spontaneously develop proteinuria and glomemlosclerosis, especially in males. We investigated the effect of castration on spontaneous proteinuria and progressive renal injury in male Imai ats. Male Imai rats (n = 16) were castrated at 5 weeks of age. Body weight, blood pressure, urinary protein excretion and semm constituents were checked and compared with sham-operated control rats (n = 16) up to 24 weeks. Sham-operated group 1 (n = 5) and castrated group 2 (n = 6) underwent morphological study after 16 weeks of observation and sham-operated group 3 (n = 11) and castrated group 4 (n = 10) were followed for an additional 8 weeks and used for morphological study. Growth rate was significantly stunted in castrated rats as compared with the controls. Castration significantly reduced proteinuria almost throughout the experiment (167 ± 84 vs. 46 ± 24 mg/kg/day, p < 0.001, at 8 weeks and 688 ± 211 vs. 458 ± 97, p < 0.01, at 20 weeks. The glomemlosclerosis index was significantly higher in sham-operated control rats than in castrated rats (28.8 ± 18.0 vs. 7.3 ± 3.1, p < 0.01, at 16 weeks, and 92.1 ± 35.5 vs. 39.5 ± 8.9, p < 0.001, at 24 weeks). There were no significant differences in blood pressure, semm cholesterol, plasma renin activity, plasma somatomedin C levels between the two groups. These results raise the possibility that sex hormones may partly contribute to spontaneous proteinuria and progressive renal injury in male Imai rats.

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Hyperlipidemic Imai rats spontaneously develop hypercholesterolemia, proteinuria and glomerulosclerosis. We investigated the effect of enalapril, an angiotensin-converting enzyme (ACE) inhibitor, on spontaneous hypercholesterolemia and the progressive renal injury in this rat strain. Male Imai rats (n = 7) were treated with enalapril at a dose of 50 mg/l in drinking water starting at 6 weeks of age. Body weight, blood pressure, urinary protein excretion and serum constituents were checked and compared with untreated controls (n = 5) up to 38 weeks of age. Enalapril treatment significantly reduced hypercholesterolemia (247 ± 41 vs. 102 ± 13 mg/d1, p < 0.01, at 38 weeks) and proteinuria (766 ± 290 vs. 206 ± 119 mg/kg/day, p < 0.01, at 38 weeks). The glomerulosclerosis index (SI) was significantly higher in untreated control rats than in the enalapril-treated group (227 ± 57 vs. 27 ± 9, p < 0.01). Although we could not clarify whether hypercholesterolemia is a primary event or secondary to the nephrotic syndrome, these results indicate that the ACE inhibitor has the property to protect remnant glomeruli from glomerulosclerosis in male Imai rats as well as in other animal models in which focal and segmental glomerulosclerosis is believed to represent a common pathologic pattern. This rat strain represents a unique model of a spontaneous proteinuria which can provide an important information on the pathogenesis of human focal and segmental glomerulosclerosis.