Progressive glomerular injury in the MWF rat is predicted by inborn nephron deficit.

It has been suggested that a reduced number of nephrons may predispose to systemic hypertension and glomerular injury. Compensatory hemodynamic changes, due to a low number of glomeruli, might be responsible for glomerular functional and structural changes. It is difficult to evaluate this hypothesis in humans because of limitations in estimating the number of nephrons in the living kidney. The aim of the present study was to estimate nephron number, single glomerular hemodynamics, and glomerular volume in male and female MWF rats, a strain that spontaneously develops systemic hypertension, proteinuria, and glomerulosclerosis. Male and female Wistar rats were used as controls. At 12 to 14 wk of age, male MWF rats developed proteinuria, whereas female MWF and Wistar rats showed normal urinary protein excretion rate. Glomerular number was significantly reduced in male and female MWF rats (13,690+/-1,489 and 12,855+/-1,781 gl/ kidney, respectively) compared with Wistar rats (26,955+/-2,171 and 27,166+/-1,754 gl/kidney, respectively). The mean number of nephrons per unit of body weight was also lower in MWF males (88+/-10) compared with MWF females (139+/-20) and compared with male and female Wistar animals (142+/-14 and 221+/-22 gl/g body wt). Whole-kidney hemodynamic parameters and the number of nephrons were used to calculate single-nephron filtration rate and plasma flow. Both measures were markedly elevated in male MWF rats relative to values obtained in the other three groups. Similarly, glomerular volume was significantly greater in MWF males than in other animals. These results suggest that an inborn deficit of nephrons may be responsible for spontaneous development of later-in-life hypertension and renal dysfunction. The data also indicate the need to investigate the role of this potential pathogenetic factor for human hypertension and kidney disease in humans.