Comparison of directly measured and calculated glomerular capillary pressure in the dog kidney at varying perfusion pressure.

To gain access to glomeruli of the dog kidney, an approximately 0.3 mm thick superficial tissue layer was cut off from the convexity of the kidney. The surface was superfused with warm Ringer's. Renal perfusion pressure (PP) was changed by an aortic clamp. The afferent oncotic pressure (pi A) was calculated from arterial plasma protein concentration, the efferent (pi E) from pi A and single nephron filtration fraction. At PP 17 and 13kPa, directly measured GCP was significantly lower than that calculated from stop-flow pressure (SFP + pi A). At PP8kPa, the difference was not significant. Hydraulic pressure differences across the glomerular capillary wall was still significantly different from pi E at PP 17 and 13 kPa. Hence, filtration pressure equilibrium was achieved in the dog kidney only at PP 8kPa.