Dialysis-induced catabolism

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Abstract
In a recent study, using both variable-volume and fixed-volume single-pool models for urea kinetics, we found that glucose in the dialysate at a level of 11 mmole/liter did not have any effect on dialysis-induced catabolism. We have now extended the investigation to determine 1) if a higher dialysate glucose level (26 mmole/liter) is any more effective in limiting intradialytic protein catabolism, and 2) by analysis of urea collected in dialysate, if the mathematical models provide accurate data on intradialytic catabolism. Cross-over studies were done on three patients between a glucose-free control and dialysates containing 11 and 26 mmole/liter glucose. Total dialyzed urea was determined from dialysate collection and 14C-urea spaces were determined on each patient at the end of the study. In 15 dialyses performed on each patient, pre/post/pre-blood samples were obtained to estimate urea generation, both intradialytically and over the dialysis cycle. Glucose was again found to be ineffective in reducing dialysis-induced catabolism. Average intradialytic urea generation was increased by 28% with glucose-free dialysis compared with 24% and 25% respectively with 11 and 26 mmole/liter glucose. There was good internal agreement between intradialytic catabolism assessed both mathematically and by dialysate urea collection. Urea spaces as measured by 14C-urea injection appeared to underestimate actual urea spaces. Normalized intradialytic catabolism was also found to be significantly correlated with predialysis serum urea levels. This strongly suggests that enzymes in the urea cycle may be inhibited by high urea levels. As the urea concentration falls during dialysis, enzyme inhibition may be reduced allowing various intermediates to enter the urea cycle at increased rates.