Effect of electric charge on the transperitoneal transport of plasma proteins during CAPD.

BACKGROUND Controversy exists as to whether electric charges of plasma proteins influence their transport across the peritoneal membrane during CAPD. Fixed negative charges in the peritoneal membrane are diminished during peritonitis in rats. METHODS Peritoneal clearances of 10 proteins and their isoforms were used to establish the relationship between peritoneal clearance and molecular weight. The observed protein clearances were compared with the predicted clearances based on molecular weight. Clearances of proteins with different charge but identical size were compared. Stable patients and peritonitis patients were compared. Results. Only the peritoneal clearance of lipase, LDH 4/5 and IgG3 were significantly different from the predicted values (P<=0.05). The peritoneal clearance of slightly anionic beta2 microglobulin (1072 microl/min) and cationic lysozyme (572 microl/min) showed no evidence for charge selectivity; neither did the peritoneal clearance of slightly anionic transferrin (86 microl/min) and highly anionic albumin (99 microl/min). The peritoneal clearance of IgG1, IgG2 and IgG4 were identical (32, 31 and 31 microl/min), despite their different charge. The peritoneal clearance of cationic LDH 4/5 was 137 microl/min and higher than the peritoneal clearance of neutral LDH 3 (97 microl/min, P=0.01) and LDH 1 (59 microl/min, P=0. 02). These results suggested charge selectivity; however in five additional patients during peritonitis the peritoneal clearance of LDH 4/5 increased to 10 times the peritoneal clearance of LDH 1. Local LDH isoenzyme release from the cells present in the dialysate was shown to be responsible in stable and peritonitis patients. Likewise, the higher peritoneal clearance of neutral pancreatic amylase (234 microl/min) compared to anionic salivary amylase (142 microl/min, P=0.03) could probably be attributed to local release of the former from the pancreas, as the peritoneal clearance of lipase (highly anionic) was higher than predicted and the difference remained during peritonitis. CONCLUSIONS The peritoneal membrane constitutes a size- but probably not a charge-selective barrier for the transport of macromolecules between blood and dialysate during stable CAPD.