Nephron number and individual glomerular volumes in male Caucasian and African American subjects.

Background: Glomerular hypertrophy has been described in several populations at high risk of chronic kidney disease. Total nephron (and thereby glomerular) number (N(glom)) varies widely in normal adult human kidneys and is generally inversely correlated with mean glomerular volume (V(glom)). However, little is known about the range of individual glomerular volumes (IV(glom)) within single human kidneys and the association with N(glom). The aim of the present study was to estimate IV(glom) in Caucasian and African Americans and identify any associations between heterogeneity in IV(glom) and nephron number.

Methods: Using unbiased stereological techniques, IV(glom) was determined for 30 glomeruli in each of 24 adult male kidneys from Jackson, MS, USA (12 Caucasian and 12 African American). Half of each group had 'high' N(glom) (>1.2 million nephrons per kidney) and the other half had 'low' N(glom) (<600 000).

Results: Caucasians with high N(glom) had a relatively homogeneous distribution of IV(glom) as well as a relatively low mean value, while those with low N(glom) had much greater heterogeneity of IV(glom), as well as a larger IV(glom) (P < 0.0001) compared with those with high N(glom). This disparity was not apparent in African Americans, however, where subjects with both high and low N(glom) showed substantial heterogeneity in IV(glom) and larger mean values (P = 0.95).

Conclusions: High N(glom) appeared to protect against glomerular enlargement and volume heterogeneity in Caucasians. However, substantial variation in IV(glom) and net enlargement in glomerular size in African Americans with high nephron numbers suggest that additional forces, independent of low N(glom), are driving glomerular enlargement and heterogeneity.