Permeability of Different Parts of the Peritoneal Mesothelium to Solutes: An in Vitro Study

The authors studied the in vitro permeability of different fragments of the rabbit's peritoneum to urea, inulin, horseradish peroxidase, and ferritin. Parietal peritoneum has a lower permeability to middle and large molecules than visceral peritoneum. In addition the local anesthetic, bupivacaine had a different effect on the mesothelial permeability of visceral peritoneum than on that of parietal peritoneum.

Endogenous Sympathetic Activity in CAPD Patients: Its Relationship to Peritoneal Diffusion Capacity

Endogenous agents, as catecholamines, may influence peritoneal mass transport by modifying peritoneal blood flow. Such endogenous mechanisms could explain certain functional peculiarities of the peritoneum in CAPD patients. In 27 randomly selected patients on CAPD we calculated peritoneal mass-transfer coefficient (MTC) for urea, creatinine, uric acid and parathormone (PTH) using mathematical modelling techniques. Also we measured simultaneously the renin-angiotensin and catecholamine levels in blood and dialysate.

The dialysate level of catecholamines and especially noradrenaline was significantly higher than the blood levels. Most of these patients had higher renin and aldosterone blood levels than the controls; we found no renin activity in the dialysate of any of these patients; (Plasma) aldosterone values correlated directly with renin activity. Multivariant analysis provided no evidence that the MTCs values were affected by two or more variables. Linear regression analysis of all variables studied showed direct correlation between dialysate noradrenaline and MTCs, and negative relationship between noradrenaline and ultrafiltration capacity. The catecholamine plasma levels, which were within the normal range, did not correlate with MTCs or with ultrafiltration.

Our findings suggest that, in some cases, noradrenaline produced in the peritoneum may influence peritoneal mass transport through a vasoactive effect. Dialysate catecholamine levels correlate with that of plasma, but the latter does not influence peritoneal transport.

Animal Models of Peritoneal Dialysis: Thirty Years of Our Own Experience

Experimental animal models improve our understanding of technical problems in peritoneal dialysis PD, and such studies contribute to solving crucial clinical problems. We established an acute and chronic PD model in nonuremic and uremic rats. We observed that kinetics of PD in rats change as the animals are aging, and this effect is due not only to an increasing peritoneal surface area, but also to changes in the permeability of the peritoneum. Changes of the peritoneal permeability seen during chronic PD in rats are comparable to results obtained in humans treated with PD. Effluent dialysate can be drained repeatedly to measure concentration of various bioactive molecules and to correlate the results with the peritoneal permeability. Additionally we can study in in vitro conditions properties of the effluent dialysate on cultured peritoneal mesothelial cells or fibroblasts. We can evaluate acute and chronic effect of various additives to the dialysis fluid on function and permeability of the peritoneum. Results from such study are even more relevant to the clinical scenario when experiments are performed in uremic rats. Our experimental animal PD model not only helps to understand the pathophysiology of PD but also can be used for testing biocompatibility of new PD fluids.

Drug therapy in continuous ambulatory peritoneal dialysis patients

Transport of solutes across the peritoneal membrane in continuous ambulatory peritoneal dialysis (CAPD) is determined by patient-related factors (concentration gradient, membrane surface area, blood flow and membrane permeability) and by drug-related factors (charge on the molecule, protein binding, molecular weight, lipophilicity). On the basis of the chemical properties of a drug a prediction of the peritoneal clearance rate in CAPD patients is given, by the formula CLCAPD = 75 square root free fraction/molecular weight. The implications of this formula are discussed. It is concluded that usually it is not necessary to change the dose as compared with end-stage renal disease patients who are not treated with CAPD.