Activation of inactive kallikrein in the rat kidney during low sodium intake

A method was developed to measure the protease responsible for activation of inactive kallikrein in the rat kidney. The renal protease was evaluated by incubating the purified rat urinary inactive kallikrein with the renal cortical extract in the presence of cysteine at pH 5.0. The renal cortical extract produced a dose- and time-dependent activation of the inactive kallikrein. Levels of the renal protease responsible for activation of inactive kallikrein remained unchanged with dietary sodium restriction. On the other hand, urinary excretion of total, active, and inactive kallikrein increased significantly during low sodium intake, with no change in the ratio of active to total kallikrein. These results suggest that low sodium intake stimulates the biosynthesis of inactive kallikrein but not the activation of this kallikrein precursor in the kidney.