Effect of Mannitol on Glomerular Ultrafiltration in the Hydropenic Rat

Abstract

A B S T R A C T The effect of mannitol upon glomerular ultrafiltration was examined in hydropenic MunichWistar rats. Superficial nephron filtration rate (sngfr) rose from 32.0±:0.9 nl/min/g kidney wt to 42.0±1.6 (P < 0.001) in eight rats. Hydrostatic pressure gradients acting across the glomerular capillary (AP) were measured in glomerular capillaries and Bowman's space with a servo-nulling device, systemic (IrA) and efferent arteriolar oncotic pressures (7rE) were determined by microprotein analysis. These data were applied to a computer-based mathematical model of glomerular ultrafiltration to determine the profile of effective filtration pressure (EFP = AP -7r) and total glomerular permeability (LpA) in both states. Filtration equilibrium obtained in hydropenia (LpA ) 0.099± 0.006 nl/s/g kidney wt/mm Hg) and sngfr rose because EFP increased from a maximum value of 4.2±t1.1 to 12.8±0.5mm Hgaftermannitol (P <0.01). This increase was due to both increased nephron plasma flow and decreased 7rA. Computer analysis of these data revealed that more than half (> 58%) of this increase was due to decreased WA, consequent to dilution of protein. Since EFP was disequilibrated after mannitol, LpA could be calculated accurately (0.065 ± 0.003 nl/s/g kidney wt/mm Hg) and was significantly lower than the minimum estimate in hydropenia.Therefore, sngfr does increase with mannitol and this increase is not wholly dependent upon an increase in nephron plasma flow since the major factor increasing EFP was decreased 7rA INTRODUCTION There is evidence from both the reijal physiology laboratory (1-4) and the clinical experience (5,6)

Acute effects of antiglomerular basement membrane antibody on the process of glomerular filtration in the rat.

“…Surgical preparation for micropuncture was as previously described in recent studies from this laboratory (11)(12)(13)(14)(15). All micropuncture studies were paired.…”

“…Methods for pressure measurement and the mechanics of the pressure monitoring device were as described previously from this laboratory (11,15). At least three samples of efferent peritubular blood were obtained from "star" vessels on the kidney surface (11)(12)(13)(14).…”

“…At least three samples of efferent peritubular blood were obtained from "star" vessels on the kidney surface (11)(12)(13)(14). Samples of femoral artery blood were also obtained concurrently in triplicate for protein determinations.…”

“…Details of the micro-adaptation of the Lowry protein method (16) have been described in previous publications from this laboratory (11)(12)(13)(14).…”

“…Protein electrophoresis of plasma samples were performed as previously described (11,12,17). Urine protein concentration was determined by the microadaptation of the Lowry protein method (16,(11)(12)(13)(14).…”