STORED RENIN ISOFORMS IN THE DEVELOPING RAT-KIDNEY

Fetal rat kidney contains renin in renal microvasculature, whereas adu lt rat kidney contains renin predominantly in juxtaglomerular cells. I t is hypothesized that renin isoforms stored within these renal tissue s may differ chemically and functionally. To test this hypothesis, sto red renin isoforms in fetal and adult rat kidney were compared by isol ating renin from adult and fetal kidney homogenate with pepstatin agar ose. Pepstatin-eluted renin isoforms were separated by relative molecu lar size using one-dimensional polyacrylamide gel electrophoresis (SDS -PAGE), or by isoelectric point (pi) and size using two-dimensional (2 D) gel electrophoresis. Isoforms were identified either by silver stai ning or immunoblotting. One-dimensional polyacrylamide gel electrophor esis of pepstatin-treated kidney homogenates showed a silver-stained b and in the range of similar to 45 kDa, which corresponded to a silver- stained spot consistently seen on 2D gels. In fetal kidney homogenate, the similar to 45 kDa band had a pi of 5.3 +/- 0.1, whereas the corre sponding band in adult samples had a basic pi of 6.0 +/- 0.05. Angiote nsin I generation was measured to assess renin enzymatic activity. The re was significantly more inactive renin in fetal kidney homogenate th an in adult kidney homogenate (60.2 +/- 22.4 v 9.6 +/- 4.0 ng AI/mg pr otein/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 activit y in fetal kidney homogenate was significantly higher than in adult ki dney 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 th ese variations in stored renin isoforms play a role in the development al differential regulation of the intrarenal renin angiotensin system. (C) 1998 American Journal of Hypertension, Ltd.