The effect of interdialytic interval on protein metabolism: evidence suggesting dialysis-induced catabolism.

While examining protein metabolism in hemodialysis patients, we noted that lengthening the interdialytic intervals from two to three days reduced the dialysate nitrogen waste excretion (D-N2; mg/min) and lowered the patient's protein catabolic rate (PCR; g/kg/d). D-N2 was measured in the spent dialysate and PCR derived from urea kinetics while patients maintained a constant dietary intake. In the basal state (B), D-N2 decreased from 5.43 to 4.32 mg/min when the interdialytic interval was increased from two to three days (P less than 0.001). Similarly, PCR was reduced from 0.96 to 0.82 g/kg/d when the interdialytic period was extended. The same phenomenon was observed when subjects were taking either thyroid hormone (T3) or ipodate (lp) to increase or decrease body metabolism. In the T3 period, D-N2 was 6.12 and 5.06 mg/min and PCR was 1.08 and 0.92 g/kg/d, respectively, when the interdialytic intervals were two and three days (P less than 0.001). During the lp period, N-D2 was 4.78 and 4.03 mg/min and PCR was 0.88 and 0.76 g/kg/d, respectively, for the two- and three-day intervals (P less than 0.05). These data are consistent with dialysis-related protein catabolism. It appears that the longer interdialytic interval allowed the body to shift to a more anabolic state.