Dynamics of glomerular ultrafiltration in the rat. II. Plasma-flow dependence of GFR.

BRENNER, B.M.,J.L. TROY, T.M. DAUGHARTY, W.M. DEEN, distance AND C. R. ROI~ERT~ON. Dynamics of glomerular ultrajltration in the a series rat. I.. Plasma-flow dependence of GFR. Am. J. Physiol. 223(5) : 1184merular 1190. 1972.-Using servo-nulling transducers and microneuver 1 l 1 ’ .1 1 l , 0.1 P 1 1. Y analytical pro tein assay metnoas in rats witn surrace glomerun, we measured glomerular capillary and proximal tubule hydrostatic pressures and estimated afferent and efferent arteriolar oncotic pressures during conditions deliberately designed to increase GFR (acute expansion of plasma and extracellular volume). Single-nephron (SN) GFR and initial glomerular capillary plasma flow (GPF) both increased approximately twofold. Net ultrafiltration pressure at the afferentmost point in the glomerulus was essentially the same prior to and following volume expansion. Similarly, filtration pressure equilibrium was achieved both prior to and following expansion. The roughly proportional changes in SNGFR and GPF provide evidence that glomerular ultrafiltration is a plasma-flow-dependent process. Under these conditions (filtration pressure equilibrium), SNGFR is determined entirely by GPF, transcapillary hydrostatic pressure difference, and initial capillary protein concentration. The possible physical mechanisms underlying the plasma-flow dependence of SNGFR have been examined using a recently developed model. along the glomerular capillary (8). We report here of measurements related to the dynamics of gloultrafiltration during one such experimental mathat of deliberately elevating GFR by means of acute expansion of plasma and extracellular volume. The results of these measurements provide evidence to indicate that glomerular ultrafiltration is a plasma-flow-dependent process. Using these measurements and the relationships derived from the mathematical model (8), it has been possible to examine the relative influences of several factors potentially responsible for this phenomenon of flow dependence.