Small-solute transport across specific peritoneal tissue surfaces in the rat

On the basis of a theoretical analysis of peritoneal transport, the tissue-specific mass transfer coefficients (MTC) for sucrose were calculated, and the MTCliver was found to be five times the magnitude of other tissue MTC. It was hypothesized that the liver was potentially the most significant single transport organ for small solutes during peritoneal dialysis. To test this hypothesis, diffusion chambers were affixed to the peritoneal surface of the rat cecum, liver, stomach, or abdominal wall to measure the in vivo bidirectional mass transfer rates of 14C-mannitol between the plasma and the fluid contained in the diffusion chambers. It was determined that the rate of mannitol transport in either direction of transport was similar for all four tissues. The MTC for plasma-to-chamber transport varied between 1.59 x 10(-3) and 2.36 x 10(-3) cm/min with MTCliver = 1.87 +/- 0.24 x 10(-3) cm/min. MTC in the opposite direction ranged between 1.73 x 10(-3) and 2.68 x 10(-3) cm/min with the MTCliver = 2.34 +/- 0.06 x 10(-3) cm/min. The authors' hypothesis concerning the MTCliver was therefore disproved. Peritoneal dialysis was also carried out in a separate series of rats, in which the area of the dissected peritoneal tissues was measured and the mass transfer-area coefficient (MTAC) for 14C-mannitol was determined to be 0.364 +/- 0.068 cm3/min (cavity to plasma) and 0.240 +/- 0.039 cm3/min (plasma to cavity). The tissue-specific MTC were then multiplied by the corresponding tissue areas and summed to estimate an MTAC of 1.0 cm3/min, which is 3 to 4 times the measured MTAC. It was concluded that the importance of a particular tissue to plasma-peritoneal transport is primarily dependent on the surface area exposed to the dialysis solution. However, only 25 to 30% of the dissected-organ tissue area may be in contact with the dialysate fluid.