Muscle protein synthesis is impaired in nephrotic rats

Muscle protein synthesis is impaired in nephrotic rats: muscle and hepatic protein synthesis was measured as the incorporation of [3H]phenylalanine [3H]phe) into muscle and liver in male Sprague-Dawley rats with passive Heymann nephritis (HN) in comparison to both normal male (SDM) and female Sprague-Dawley rats (SDF). Incorporation of [3H]phe was significantly less muscle in HN (1.55 +/- 0.08 x 10(4) cpm/g muscle/h) than in SDM (2.55 +/- 0.14 x 10(4), p < 0.01) and no different than in SDF (1.64 +/- 0.23 x 10(4)). Growth rate was also significantly less in SDF and HN compared to SDM. Total [3H]phe incorporation and the % of [3H]phe incorporated into muscle correlated inversely with urinary albumin excretion in HN (p < 0.01) but not with serum albumin. In contrast, [3H]phe incorporation was increased in livers of HN (13.89 +/- 0.99 x 10(3) cpm/g rat/h) compared to either SDM (5.96 +/- 0.38 x 10(3), p < 0.01) or SDF (4.71 +/- 0.35 x 10(3), p < 0.01). Total liver mass, liver protein content, and the ratio of liver weight/body weight were all increased in HN. There were no differences in liver weight, liver protein content, or the ratio of liver weight/body weight between SDM and SDF. We have previously shown that decreased muscle protein accrual in HN cannot be overcome by increasing dietary protein intake. Hepatic protein synthesis and mass are increased in proteinuric rats while muscle protein synthesis is reduced. As a consequence growth rate and muscle protein accrual are diminished in nephrosis. The mechanism responsible for reduced muscle protein synthesis in the nephrotic syndrome is unknown.