Effects of Ringer fluid on regional blood flow and filtration rate in the cat kidney

The larger subcapsular veins of the in situ cat kidney were cut open near the hilus and occluded between the slits and the common renal vein, thus permitting separation and direct measurement of venous outflows from the superficial (outer cortex) and deep (inner cortex plus medulla) drainage area. The direct recording of venous outflow in the two areas combined with plasma inulin and protein analyses provided consecutive determinations of the rate of glomerular filtration and arterial inflow of both areas. Our primary result is the demonstration of a regional difference in the renal response to extracellular isotonic volume expansion. Infusion of Ringer fluid at a moderate rate (1.0-2.0 ml X min-1) increased both blood flow (RBF) and glomerular filtration rate (GFR) in both areas; however, the RBF response was proportionately greater in the deep area and the GFR response was proportionately greater in the superficial area. Compared with a noninfused control series, statistically significant differences occurred after about 1 h of infusion. After 80 min, average RBF had increased by 33 and 20%, while average GFR had increased by 31 and 54% in the deep and in the superficial areas, respectively. To reveal direct renal effects of the Ringer fluid, the site of infusion was shifted alternately between the renal artery and the jugular vein. The results suggest that the changes in blood flow are elicited indirectly by neural or humoral mechanisms.