Charge-affected transperitoneal movement of amino acids in CAPD

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.