High level of plasma inactive renin in Bartter's syndrome

In 10 cases of Bartter's syndrome, plasma active and inactive renin (AR and IR) were measured by two different methods. First, plasma renin activity (PRA), and total renin activity (TRA) after activating IR with trypsin, were measured by radioimmunoassay (RIA) of angiotensin I (AI) generated from endogenous substrate. And secondly, plasma active renin concentration (ARC) and total renin concentration (TRC) were measured by RIA of AI generated in the presence of an excess of exogenous substrate. The difference between TRA and PRA, and between TRC and ARC were designated as inactive renin activity (IRA) and inactive renin concentration (IRC), respectively. Small amounts of IRA were found only in 2 cases and no IRA in 8 cases. However, the existence of large amounts of IR in Bartter's syndrome was revealed by the IRC determination. This suggests that the shortage of endogenous renin substrate, consumed by the markedly increased AR, may have interfered with the detection of IRA in Bartter's syndrome, though the IR is markedly increased as well. The molecular weights of AR and IR were determined by Sephadex G-100 gel filtration in 3 cases. Both AR and IR seemed to be smaller than those of normal subjects.