Stored Renin Isoforms in the Developing Rat Kidney

Fetal rat kidney contains renin in renal microvasculature, whereas adult rat kidney contains renin predominantly in juxtaglomerular cells. It is hypothesized that renin isoforms stored within these renal tissues may differ chemically and functionally. To test this hypothesis, stored renin isoforms in fetal and adult rat kidney were compared by isolating renin from adult and fetal kidney homogenate with pepstatin agarose. Pepstatin-eluted renin isoforms were separated by relative molecular size using one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE), or by isoelectric point (pI) and size using two-dimensional (2D) gel electrophoresis. Isoforms were identified either by silver staining or immunoblotting. One-dimensional polyacrylamide gel electrophoresis of pepstatin-treated kidney homogenates showed a silver-stained band in the range of approximately 45 kDa, which corresponded to a silver-stained spot consistently seen on 2D gels. In fetal kidney homogenate, the approximately 45 kDa band had a pI of 5.3 +/- 0.1, whereas the corresponding band in adult samples had a basic pI of 6.0 +/- 0.05. Angiotensin I generation was measured to assess renin enzymatic activity. There was significantly more inactive renin in fetal kidney homogenate than in adult kidney homogenate (60.2 +/- 22.4 v 9.6 +/- 4.0 ng AI/mg protein/h, P < .05). There was significantly less active renin in fetal kidney homogenate than in adult kidney homogenate (5.4 +/- 0.4 v 36.5 +/- 14.2 ng AI/mg protein/h, P < .05). The average total renin activity in fetal kidney homogenate was significantly higher than in adult kidney homogenate (65.6 +/- 22.3 v 46.0 +/- 15.2, P < .05). These results demonstrate major differences in the physical and enzymatic forms of stored renin found in fetal and adult kidney. It is speculated that these variations in stored renin isoforms play a role in the developmental differential regulation of the intrarenal renin angiotensin system.