Elevation of plasma angiotensinogen in rats with experimentally induced nephrosis

In order to determine the activity of the renin-angiotensin system in the nephrotic syndrome, the plasma concentration of angiotensinogen was measured in rats with puromycin aminonucleoside (PA)-induced nephrosis using two different methods: a direct radioimmunoassay, which measures both angiotensinogen and des-angiotensin I-angiotensinogen, and an indirect assay, which measures angiotensin I liberated from angiotensinogen by excess renin. The plasma concentration of angiotensinogen as measured by the direct assay increased before the appearance of PA-induced hypoproteinemia or proteinuria and subsequently decreased to normal levels simultaneously with the appearance of proteinuria. The indirect assay of angiotensinogen also demonstrated an increased concentration of plasma angiotensinogen before the development of nephrosis, but the level decreased to below normal after the appearance of proteinuria. Both plasma renin concentration and renin activity also increased simultaneously with the increase in plasma angiotensinogen. The difference between the concentrations of plasma angiotensinogen determined by these methods increased before and during the early phase of PA-induced nephrosis, suggesting the increased consumption of angiotensinogen by renin during this period. Measurement of plasma corticosterone and serum interleukin-6 revealed that these circulating factors were not involved in the elevation of plasma angiotensinogen in rats with PA-induced nephrosis. These results indicate that the renin-angiotensin system is activated before the appearance of PA-induced nephrotic syndrome.