OF ELECTRIC CHARGE ON THE TRANSPERITONEAL TRANSPORT OF PLASMA-PROTEINS DURING CAPD

Background. Controversy exists as to whether electric charges of plasm a proteins influence their transport across the peritoneal membrane du ring CAPD. Fixed negative charges in the peritoneal membrane are dimin ished during peritonitis in rats. Methods. Peritoneal clearances of 10 proteins and their isoforms were assessed in CAPD patients. The most neutral proteins were used to establish the relationship between perit oneal 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. Resu lts. Only the peritoneal clearance of lipase, LDH 4/5 and IgG3 were si gnificantly different from the predicted values (P less than or equal to 0.05). The peritoneal clearance of slightly anionic beta(2) microgl obulin (1072 mu l/min) and cationic lysozyme (572 mu l/min) showed no evidence for charge selectivity; neither did the peritoneal clearance of slightly anionic transferrin (86 mu l/min) and highly anionic album in (99 mu l/min). The peritoneal clearance of IgG1, IgG2 and IgG4 were identical (32, 31 and 31 mu l/min), despite their different charge. T he peritoneal clearance of cationic LDH 4/5 was 137 mu l/min and highe r than the peritoneal clearance of neutral LDH 3 (97 mu l/min, P=0.01) and anionic LDH 2 (65 mu l/min, P=0.01) and LDH 1 (59 mu l/min, P=0.0 2). These results suggested charge selectivity; however in five additi onal patients during peritonitis the peritoneal clearance of LDH 4/5 i ncreased to 10 times the peritoneal clearance of LDH 1. Local LDH isoe nzyme release from the cells present in the dialysate was shown to be responsible in stable and peritonitis patients. Likewise, the higher p eritoneal clearance of neutral pancreatic amylase (234 mu l/min) compa red to anionic salivary amylase (142 mu l/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 predi cted and the difference remained during peritonitis. Conclusions. The peritoneal membrane constitutes a size- but probably not a charge-sele ctive barrier for the transport of macromolecules between blood and di alysate during stable CAPD.