Intrarenal Arterial Network Renin Content and Inhibition by EMD 58265

The renin content, expressed as nanograms of angiotensin I/hour/milligram, of a rabbit intrarenal arterial network (IAN) was compared to that of renal cortical samples from the same animal. Tissues from six rabbits were studied. Cortical tissue (RC) and an IAN with some glomeruli and attached arterioles (IAN + glomeruli) were prepared from one kidney, and an IAN freed of glomeruli (IAN − glomeruli) was obtained from the opposite kidney. These tissues were homogenized and the supernatant incubated at pH 7.4 and 37°C for 30 to 60 min or 3 to 6 h. Angiotensin I was generated in a linear fashion, and the values averaged for the two incubation periods were 844 ± 266, 121 ± 39, and 32 ± 11 ng/h/mg for RC, IAN + glomeruli, and IAN − glomeruli, respectively. A specific renin inhibitor, EMD 58265, at 1 × 10−8 mol/L attenuated and at 5 × 10−8 mol/L almost totally abolished angiotensin I production. The results indicate that small arteries comprising the IAN contain renin, and that the enzymatic activity is most likely due to that protein and not another aspartyl protease.