ENHANCED PERITONEAL DIFFUSION CAPACITY OF CR-51-EDTA DURING THE INITIAL PHASE OF PERITONEAL-DIALYSIS DWELLS - ROLE OF VASODILATATION, DIALYSATE STIRRING, AND OF INTERSTITIAL FACTORS

Mass transfer area coefficients (PS) to small solutes are usually mark edly increased during the first 0-15 min of peritoneal dialysis (PD) d wells. This phenomenon may be due to, for example, initial arteriolar vasodilatation and, hence, recruitment of capillary surface area. Othe r possibilities are an initial discharge (or saturation) of solutes fr om (in) the interstitium or an increased mixing, i.e., 'macrostirring' caused by the exchange procedure per se. We have investigated these p ossibilities during acute PD in rats, by assessing PS for Cr-51-EDTA a s a function of time [PS(t)]. The discharge effect was studied by satu rating the peritoneal interstitium with Cr-51-EDTA by intravenous trac er infusion prior to each dwell and the results compared to those obta ined in rats when tracer infusion and dwells were started simultaneous ly. The potential effect of initial vasodilatation was studied by addi ng isoproterenol to the dialysis fluid. Finally, the potential influen ce of an increased interstitial 'microstirring', induced by high gluco se concentrations, was investigated by comparison of results for 1.36% Dianeal(R) with those for 3.86% Dianeal. In nonvasodilated rats there was a significant drop in PS(t) between 2.5 and 15 min regardless of whether the rats were preloaded with tracer or not. However, there wer e no significant changes in PS(t) within the isoproterenol-treated gro up, indicating that vasodilatation plays a crucial role for the high P S initially. Furthermore, there was no difference in overall PS for Cr -51-EDTA among 1.36 and 3.86% Dianeal dwells. In conclusion, we have f ound that vasodilatation, but not interstitial discharge (or loading), may explain the inflation of PS occurring during the initial part of PD dwells. In addition, 'macrostirring', induced by the exchange proce dure per se, may also be important.