AJP - Renal Physiology, Vol 248, Issue 2 247-F253, Copyright © 1985 by American Physiological Society
Plasma volume expansion is necessary for edema formation in the rate with Heymann nephritis
G. A. Kaysen, T. T. Paukert, D. J. Menke, W. G. Couser and M. H. Humphreys
Edema formation in nephrotic syndrome has been attributed to intravascular
volume depletion resulting from leakage of plasma water into the
interstitial space and activating secondary renal sodium retention.
However, clinical studies indicate that edematous patients with nephrotic
syndrome may have normal or expanded plasma volumes. We evaluated the
relationship between plasma volume and edema formation in control rats and
rats with chronic renal failure (CRF) produced by 7/8 nephrectomy. In each
group, plasma volume and 22Na space were measured during the control period
and after induction of hypoalbuminemia from passive Heymann nephritis. Rats
with CRF had expanded plasma volume during the initial period (4.23 +/-
0.46 vs. 3.32 +/- 0.68 ml/100 g body wt) that became significantly more
expanded (to 5.44 +/- 1.16 ml/100 g body wt) when they became nephrotic as
22Na space also increased. Plasma volume and 22Na space did not change in
the sham-operated rats when nephrosis was produced. Plasma renin activity
was lower in the CRF rats during the control period than in the
sham-operated rats and fell significantly during the nephrotic period when
edema developed. Nonnephrotic rats had a plasma colloid osmotic pressure
(COP) of 17.8 +/- 4.3 mmHg compared with 8.5 +/- 2.9 mmHg when nephrotic.
Despite this large difference in COP, both nephrotic and nonnephrotic rats
exhibited the same relationship between plasma volume and extravascular
sodium space, a measure of edema formation. Hypoproteinemia is not
sufficient for edema formation in the rat with passive Heymann nephritis;
concomitant plasma volume expansion resulting from CRF is a necessary
additional component.
