Blood flow limitation in vivo of small solute transfer during peritoneal dialysis in rats

The aim of this study was to determine whether or to what extent transperitoneal flux of small solutes is reduced at low blood flows during peritoneal dialysis (PD) in rats. Peritoneal blood flow reductions were achieved by bleeding anesthetized (300 g) rats by 25% of their blood volume. After bleeding, a 2 h PD dwell was started using standard PD fluid. The permeability-surface area product (PS) for (51)Cr-EDTA and glucose were assessed, as well as the transperitoneal clearance (Cl) of albumin. Control animals were not bled. After bleeding, peritoneal blood flow declined from 145 +/- 17 perfusion units (PU) to 59 +/- 12 PU (P = 0.001). Concomitant with this reduction, PS for (51)Cr-EDTA fell from 0.284 +/- 0.01 ml/min to 0.216 +/- 0.01 ml/min (P = 0.006) and PS for glucose from 0.338 +/- 0.02 ml/min to 0.294 +/- 0.01 ml/min (P = 0.046). Mean arterial BP (MAP) dropped from 133 +/- 4 mmHg to 61 +/- 5 mmHg (P = 0.008). Cl of albumin fell largely in proportion to the estimated capillary hydrostatic pressure drop, i.e., from 6.1 +/- 0.7 microl/min to 2.3 +/- 0.3 microl/min (P = 0.001). The results demonstrate that the transperitoneal clearances of small solutes are blood flow limited during PD, when peritoneal perfusion is markedly reduced. The level of flow limitation was, however, much lower than expected and observed in other tissues. Albumin transport, which is not blood flow limited, was reduced largely in proportion to the calculated capillary hydrostatic pressure decrease.