Background: Reductions in renal filtration surface area (FSA) have been linked to development of hypertension. This study investigated whether there are direct relationships, in the adult rat, between levels of blood pressure and nephron number or total renal FSA.
Methods: F1 and F2 offspring were generated from a spontaneously hypertensive rat (SHR)/Wistar Kyoto (WKY) rat cross. Tail-cuff systolic blood pressure was measured twice weekly from 5 to 15 weeks of age and mean arterial blood pressure determined prior to sacrifice. At 15 weeks of age, the rats were perfusion-fixed and glomerular (and thereby nephron) number, glomerular size, total length, and surface area of glomerular capillaries and total renal FSA were determined using unbiased stereologic techniques.
Results: In F1 offspring, blood pressure levels were midway between the SHR and WKY rats. Nephron number was significantly higher in the WKY rats compared to the SHR and F1 offspring. However, there was no difference in nephron number between the F1 rats and SHR and no difference in renal FSA between the three groups. In the F2 generation, where there is random segregation of the SHR and WKY genes, there was no significant correlation between either nephron number and adult blood pressure (r2= 0.16, P= 0.11) or total renal FSA and adult blood pressure (r2= 0.02, P= 0.58). There was a significant inverse correlation between nephron number and glomerular size (r2= 0.49, P= 0.0043).
Conclusion: There is not a direct corollary between nephron number or renal FSA and level of blood pressure in this rat model.