EFFECTS OF RENAL-FAILURE ON SKELETAL-MUSCLE

In this cross-sectional study, we examined biopsies from the vastus lateralis muscle of 13 predialytic uremic men (mean age 46 +/- 8 years). Their average glomerular filtration rate was 14 +/- 7 ml/min x 1.73 m2 and their maximal exercise capacity, measured by standardized exercise test on a bicycle ergometer, was 184 +/- 45 W (94% of the expected norm). The proportion of type I fibers (type I%) in the uremic group was similar to that of the reference group (42 +/- 11 vs. 41 +/- 8% NS). The proportion of type IIA fibers (type IIA%) in the uremic group was higher than in the reference group (44 +/- 10 compared to 35 +/- 9%, p < 0.05). The proportion of type IIB fibers (type IIB%) was lower than in the reference group (13 +/- 8 vs. 21 +/- 8%, p < 0.05). Type I fiber area was similar to that of the reference group (4,768 +/- 1,033 vs. 4,627 +/- 1,112 mum2, NS). Type IIA and type IIB fiber areas tended to be smaller than those of the reference group (type IIA fiber area: 4,515 +/- 929 vs. 5,213 +/- 1,288 mum2, NS; type IIB fiber area: 3,953 +/- 1,066 vs. 4,406 +/- 1,582 mum2, NS) with a type IIA area/type I area ratio which was significantly lower than in the reference group. Citrate synthase activity was 0.48 +/- 0.08 mukat/g in the uremic group and 0.50 +/- 0.08 mukat/g in the reference group, NS. Phosphofructokinase activity was 1.2 +/- 0.5 mukat/g in the uremic group and 1.1 +/- 0.3 mukat/g in the reference group, NS. Maximal exercise capacity showed a positive correlation to type 1% (r = 0.71, p < 0.01) and a negative correlation to type IIA% (r = -0.73, p < 0.01). In multiple regression analysis, type 1% showed a negative correlation to GFR, when maximal working capacity had been accounted for (r = -0.83, p < 0.005). The observed increase in type IIA% at the expense of type IIB% in conjunction with the negative correlation between type 1% and GFR may indicate a relationship between progressive uremia and muscle fiber composition, which may lead to a reduced exercise capacity.