Serum renotropic activity and renal growth in spontaneously hypertensive rats.

Studies performed in the 1950's suggested that a circulating factor controlling renal growth (renotropin) could contribute to hypertension. However, no assay was available to prove its existence. Recently, different assays have been able to demonstrate the presence of a circulating renotropic factor following unilateral nephrectomy in rats. Therefore, we investigated certain aspects of renal growth in SHR, especially serum renotropic activity, and compared these with the same parameters in three strains of normotensive rats (SD, NWR, and WKY). Renal slice and renal DNA synthesis in response to unilateral nephrectomy were not unusual in SHR compared to other strains previously studied. Sera and renal extracts from young SHR following unilateral nephrectomy compared to sera and renal extracts from sham-operated SHR stimulated 3H-thymidine incorporation into the DNA of renal fragments. This pattern was similar to findings when sera and renal extracts from unilaterally nephrectomized SD were investigated, but the sera and extracts from SHR may have shown greater overall stimulation. Interestingly, a relative increase in renotropic activity was found in the serum of untouched SHR (11.1% +/- 1.7 (SEM), P less than 0.001) but not untouched NWR, SD, and WKY. The greatest renotropic activity in SHR was found at 6 to 16 weeks of age (13.5% +/- 2.1 (SEM), P less than 0.001). The previously reported activator found in renal tissue after unilateral nephrectomy was not found to be increased in untouched SHR. No studies were performed on SHR greater than 25 weeks of age. As a first approximation, our investigations are consistent with a previously hypothesis that renotropin may play some role in hypertension.