Albuminuria causes lysozymuria in rats with Heymann nephritis

F. N. Hutchison, G. A. Kaysen

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To determine if changes in dietary protein intake alter renal excretion of small molecular weight proteins in passive Heymann nephritis, 21 rats with passive Heymann nephritis were fed 8.5% protein for 12 days after injection with antiserum. Dietary protein intake was then increased to 40% in 10 rats (LP-HP) while 11 rats remained on 8.5% protein (LP-LP). Lysozymuria (U(lys)V) increased from 66.5 ± 31.0 mcg/day to 457.5 ± 98.0 mcg/day (P < 0.001) after five days in LP-HP, but was unchanged in LP-LP. Albuminuria (U(alb)V) increased only in LP-HP, from 168 ± 23 mg/day to 447 ± 45 mg/day (P < 0.001). Urinary lysozyme excretion correlated with U(alb)V (r = 0.737, P < 0.001), and changes in U(lys)V correlated with changes in U(alb)V (r = 0.657, P < 0.01). To determine whether the increase in U(lys)V was the direct effect of the change in diet, enalapril 40 mg/kg/day was administered to prevent the increase in U(alb)V that occurs when these rats are fed a high protein diet. Twelve rats were fed 8.5% (LP) and 10 were fed 40% protein (HP) from the time of injection with antiserum. Six LP (LPE) and five HP (HPE) received enalapril. U(lys)V was 873 ± 391 mcg/day in HP and nearly undetectable in the other three groups. U(alb)V was signifithecantly greater in HP (368 ± 60 mg/day) compared to the other three groups (114 ± 16 in LP, 136 ± 44 in HPE, 95 ± 21 in LPE). A third group of nephrotic rats, maintained on a constant diet of 21% protein had enalapril added to their drinking water. U(lys)V decreased from 49 ± 9 mcg/day to less than 2 mcg/day (P < 0.001) and U(alb)V decreased from 516 ± 67 to 183 ± 32 mg/day (P < 0.001). Both U(lys)V and U(alb)V remained unchanged in untreated rats. Lysozyme, an enzyme normally entirely reabsorbed by the kidney, is found in the urine of rats with passive Heymann nephritis, and increases when dietary protein intake is increased. High protein diets increase U(lys)V only in as much as U(alb)V is increased, and when U(alb)V is reduced by use of an angiotensin converting enzyme inhibitor in the presence of a high protein diet U(lys)V is reduced in a parallel fashion, suggesting that albuminuria itself decreases the capacity of the renal tubule to reabsorb lysozyme.

Original languageEnglish (US)
Pages (from-to)787-791
Number of pages5
JournalKidney International
Issue number4
StatePublished - 1988

ASJC Scopus subject areas

  • Nephrology


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