Indirect assessment of glomerular capillary pressure from pressure-natriuresis relationship: comparison with direct measurements reported in rats.

Abstract

It is examined whether glomerular hemodynamics can be indirectly estimated from the pressure-natriuresis relationship. There are only two animal studies reported, one in normal and the other in 5/6 nephrectomized Munick-Wistar rats, which permits plotting the pressure-natriuresis relationship and comparison of indirect estimations with directly measured glomerular hemodynamic data. Normal and extensive renal ablation rats were placed on relatively high and low sodium diets. Plotting mean arterial pressure (MAP) on the x-axis and 24 h urinary sodium excretion rate on the y-axis, the pressure-natriuresis relationship was drawn. As the difference between MAP (121 +/- 1 and 169 +/- 12 mmHg) on relatively high sodium diet and the extrapolated x-intercept (122 and 138 mmHg) of the pressure-natriuresis relationship, based on previous proposal, the effective filtration pressure across the glomerular capillary walls was estimated to be-1 and 31 mmHg for normal and 5/6 nephrectomized rats. Then, the glomerular capillary hydraulic pressure (PGC) was calculated to be 33 and 64 mmHg. Micropuncture studies showed that directly measured PGC of 47 +/- 1 and 65 +/- 2 mmHg was close agreement with those estimated indirectly. Therefore, an approach from the pressure-natriuresis relationship provides a noninvasive means to predict an approximation of PGC. This approach to estimating glomerular hemodynamics may have invaluable implications for clinical practice; in the early detection of loss of filtration capacity and in the assessment of an important risk factor for the development of chronic renal failure.