Failure of An Acute 10-15% Plasma Volume Expansion in the Virgin Female Rat to Mimic the Increased Glomerular Filtration Rate (GFR) and Altered Glomerular Hemodynamics Seen at Midterm Pregnancy

Abstract

Virgin female Munich-Wistar rats were acutely plasma volume expanded (10-15% above control) and were studied by whole kidney and glomerular micropuncture techniques in control and volume expanded state. The magnitude of the plasma volume expansion was similar to that reported earlier in 9 day pregnant rats. With acute plasma volume expansion in the present study, GFR, single nephron (SN)GFR and glomerular plasma flow rate remained unchanged while glomerular blood pressure and tubule hydrostatic pressure rose. These changes are quite different to the marked rise in GFR, SNGFR and glomerular plasma flow rate, and slight fall in glomerular blood pressure that occur in the 9 day pregnant rat. It therefore seems likely that the glomerular hemodynamic changes of pregnancy are not the direct result of the moderate 10-15% plasma volume expansion evident at day 9 of gestation, a time when the GFR increment are maximal. Other renal vasodilator agents must be the functionally important mediators of the gestational rise in GFR.