Dynamics of Glomerular Ultrafiltration in the Rat V. RESPONSE TO ISCHEMIC INJURY

Abstract

A B S T R A C T An experimental model of postischemic, acute renal failure has been developed in Wistar rats with surface glomeruli, thereby making possible a direct assessment of the mechanisms responsible for the fall in glomerular filtration rate that characterizes this disorder. Whole kidney and cortical single nephron filtration rates were reduced proportionately, on average by approximately 40%, after 3 h of nearly complete occlusion of the ipsilateral renal artery. The possibility of a significant transtubular leak of inulin was excluded. This decline in filtration rate occurred in the absence of measured changes in mean arterial pressure, mean glomerular transcapillary hydrostatic pressure, or net ultrafiltration pressure at afferent and efferent ends of the glomerular capillary. Net ultrafiltration pressure at the efferent end of the capillary approached zero both before and after ischemic injury, demonstrating that filtration pressure equilibrium was achieved throughout this study. Single nephron filtration fraction remained unchanged, indicating that the fall in filtration rate was accompanied by a proportional decline in glomerular plasma flow. The results indicate that the fall in filtration rate was solely the consequence of this fall in glomerular plasma flow. Since filtration rate per nephron is equal to the product of the ultrafiltration coefficient and mean ultrafiltration pressure, this product must also have fallen in proportion to the decline in glomerular plasma flow. Evidence is presented to indicate that a change in ultrafiltration coefficient is not required to This work has been published in abstract form. 1973. Clin. Res.

Permselectivity of of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using neutral dextran.

“…This evidence that fractional dextran clearances for the kidney as a whole provide an accurate measure of dextran permeation across capillaries of a single glomerulus makes it possible to characterize the glomerular transport of dextrans of widely varying (24)(25)(26)(27)(28)(29). SNFF in NSN rats was reduced despite the fact that glomerular capillary hydraulic pressure, PGC (Table II), and the mean transcapillary hydraulic pressure difference, AP, (19,31).…”

Effect of increased peritubule protein concentration on proximal tubule reabsorption in the presence and absence of extracellular volume expansion.

“…Blantz, Rector, and Seldin (29) have shown, by direct measurement of superficial glomerular pressures, that an infusion of hyperoncotic albumin resulted in an increase in glomerular capillary permeability, thereby offsetting the increased glomerular capillary oncotic pressure. Changes in both efferent and afferent arteriole resistances have been demonstrated as determinants of single nephron filtration rate (30). Thus afferent dilatation and efferent constriction may have increased glomerular capillary pressure sufficient to offset the increased glomerular capillary oncotic pressure and hence autoregulated both sniff and single nephron plasma flow.…”

Determinants of glomerular filtration in experimental glomerulonephritis in the rat.

“…To obtain estimates of colloid osmotic pressure (7r) of plasma entering and leaving glomerular capillaries, protein concentrations (C) in femoral arterial and efferent arteriolar blood plasma were measured as described previously (1)(2)(3)(4)(5)(6). C measured in femoral arterial plasma was taken as representative of C for the afferent arteriole.…”

“…This shortcoming is due in large part to the fact that glomeruli are rarely encountered as surface structures in the mammalian kidney and are therefore inaccessible to direct study in vivo. This restriction has been overcome, however, in that a unique strain of Wistar rats with surface glomeruli has recently been discovered, allowing direct assessment of the determinants of ultrafiltration (1)(2)(3)(4)(5). Accordingly, the present study was undertaken in an effort to examine, by using previously described micropuncture techniques (1)(2)(3)(4)(5)(6), the …”