Glomerular filtration and fluid balance in genetically hypertensive mice

The Schlager genetically hypertensive mouse has been shown to be a valuable animal model with which to study human essential hypertension. Previous studies have characterized renal morphology, juxtaglomerular index, hematocrit, prostaglandin levels, brain catecholamines, social behavior, and patterns of inheritance. The present study continues the phenotypic characterization of this animal model. Using desiccation, isotope dilution, and clearance, the total body water, extracellular fluid volume, and glomerular filtration rate (GFR) in hypertensive and normotensive animals during normal postnatal development were measured. Additionally, using an electron microscopic tracer, the relative permeabilities of the glomerular filter in these animals were assessed. The data indicate a volume expansion in the young hypertensive animals along with a reduction in GFR. As the animals mature the volume expansion in the hypertensives subsides and is eventually reversed resulting in a lower than normal fluid volume level. The significance of the reduced GFR in the hypertensives is also diminished with age although not to the same degree as that of the fluid volume. The indication of a reduced glomerular permeability may account for the above in light of Guyton's cascade hypothesis.