Renal transplantation in the rat. IV. Cortical pressure gradients measured in vivo and during isolated perfusion with reference to renal function after transplantation.

Pressure characteristics within the renal cortex of rats were studied with a micropuncture technique in vivo and during isolated hypothermic perfusion. Use of a colloid-free perfusate resulted in an interstitial pressure of 30 cm H2O (normally 1-2 cm H2O), thereby producing a high outflow resistance and perfusion pressure. Interstitial pressures only slightly above normal were found when colloids such as Dextran 40 or albumin were added. The main resistance within the renal vascular bed both in vivo and during isolated perfusion was localized to the afferent and efferent arterioles. The increased pressures were most likely due to extravasation of fluid. With regard to the colloid-containing perfusates, the small but significant increase in interstitial pressure could be explained by increased passage of colloids over the capillary membranes. In conclusion, colloid-free perfusion produced a pronounced but transient elevation of the postoperative serum creatinine level in renal transplant recipients.