Effects of genetic obesity on renal structure and function in the Zucker rat

Although hyperphagia and obesity in the Zucker rat strain have been reported to be associated with spontaneous focal glomerulosclerosis (FGS), little is known about the age of onset and the natural history of hypertension, albuminuria, renal function, and glomerular injury in this model. We systematically investigated renal structure and function in obese male Zucker rats. Lean male littermates were used as controls. Obese rats developed glomerular mesangial matrix expansion and albuminuria by 14 weeks of age. These changes occurred despite normal inulin clearance (2.2 +/- 0.6 ml/min obese vs. 2.0 +/- 0.4 ml/min lean, P greater than 0.1) and filtration fraction (0.32 +/- 0.08 obese vs. 0.34 +/- 0.06 lean, P greater than 0.1), suggesting that increased glomerular filtration and renal plasma flow were not a prerequisite for the development of FGS. By 28 weeks of age, FGS was evident in seven of eight obese rats, and at 68 weeks of age all obese rats had marked FGS. Mean systolic blood pressure was elevated by 11 to 25 mm Hg in obese rats at all ages. Although the pathogenesis of glomerular injury is unknown, our data demonstrate that microalbuminuria, mild hypertension, and mesangial matrix expansion precede the development of progressive FGS in obese Zucker rats.