Our objective was to investigate the influence of molecular charge on transperitoneal solute movement in continuous ambulatory peritoneal dialysis (CAPD). Tests of peritoneal equilibration were performed. Two liters of 2.27% or 2.5% glucose CAPD dialysate were infused and the dialysate samples were taken after 2 hr and 4 hr, and blood samples were obtained after 4-hr dwell time. Dialysate-to-plasma concentrations ratios (D/P) were calculated for creatinine (Cr) and three amino acids with almost the same molecular weight but quite different charges: glutamic acids (Glu: negatively charged), glutamine (Gln: near neutrally charged), and lysine (Lys: positively charged). The setting was a university hospital. There were 23 stable CAPD patients with a mean age of 56.6 +/- 9.5 years and a mean CAPD duration of 15.2 +/- 19.4 months. D/P ratio of Glu was much lower than those of Gln, Lys and Cr at both 2 hr and 4 hr (p < 0.01), and D/P of Lys was significantly lower than that of Gln (p < 0.01). There was no significant difference of D/P between Gln and Cr. The order of transperitoneal mobility among the three amino acids was Gln > Lys > Glu. Transperitoneal movement of solutes in CAPD is influenced by molecular charge, the movement of negatively charged solutes is most remarkably retarded in cases of amino acids.

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