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Abnormal Increase of Creatine Kinase Plasma Levels following Muscle Exercise in Nephrotic Patients

Nephrotic syndrome is a protein-wasting disorder affecting total body protein metabolism, often leading to reduction of lean body mass and changes of muscle cell composition. The aim of this study was to investigate the susceptibility to muscle cell damage in nephrotic patients following submaximal physical exercise, by detection of the creatine kinase (CK) plasma level changes. Fourteen patients affected by primary nephrotic syndrome, without chronic renal failure, underwent an exercise test on a cycle ergometer for 20 min at a constant speed (60 rpm). In each subject, the work rate (expressed as watts) was established as 70% of the maximum power theoretically calculated on a sex, age, weight and height basis. CK plasma levels (U/l) were determined before and 1, 3, 6 and 24 h after the exercise. Following exercise, CK plasma levels became higher in nephrotics than in normal controls. That is, the amount of CK increments was greater in nephrotics than in controls from the first hour after the end of exertion. These changes, both as absolute values and as percentage of the basal values, correlate positively to daily urinary protein losses; moreover, an inverse relationship was detected with albumin serum levels. However, no correlation was observed between the amount of plasma CK increases and age, body weight, plasma creatinine, plasma cholesterol or hemoglobin levels. These results demonstrate that a greater than normal increase of CK plasma levels occurs in nephrotics following physical exercise, and that this increment correlates with the severity of urinary protein wasting. This suggests an increased susceptibility to muscle injury in nephrotic patients probably related to protein depletion and/or to modifications of muscle cell metabolism. Further studies are needed to define the pathogenesis of our findings.