ObjectiveA reduced number of nephrons, whether acquired or congenital, as has been observed in certain inbred rat strains, may lead to systemic hypertension. The present study estimated the total number of glomeruli and mean glomerular size in kidneys of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.MethodsUnbiased stereological methods were used on immersion-fixed kidneys from 12-week-old male SHR (n = 9) and age-matched WKY rats (n = 11).ResultsThe total number of glomeruli was significantly reduced in the SHR compared with in the WKY rats. Sclerotic glomeruli were not found in either group. No significant difference in mean glomerular volume was observed, but the total glomerular volume was reduced by 25% in the SHR compared with in the WKY rats.ConclusionSHR have fewer glomeruli than WKY rats, but of similar size, resulting in a reduced total glomerular volume in adult SHR. These findings are consistent with the hypothesis that the kidney plays an important role in the pathogenesis of genetic hypertension.