Segmental localization of kallikrein-like pro-phe-arg-naphthylester esterase in the rat nephron

A synthetic substrate for kallikrein, pro-phe-arg-naphthylester, was used in order to identify histochemically kallikrein-like enzyme-containing segments of the nephron in the rat kidney. The localization was technically facilitated by comparing sections histochemically incubated with neighbouring freeze-dried sections and by semiquantitative evaluation of the enzyme activity performed. In the proximal tubules, the enzyme activity increased from the first segment to the third segment which exhibited the most pronounced activity encountered. In the proximal convoluted tubules the enzyme activity was present mainly in the deep half of the cortex. This was generally weaker in the other segments of the nephron where enzyme activity was present. In the descending thin limb of Henle, weak activity was noticed in a few initial segments. However, in the ascending thick limb of Henle, more pronounced enzyme activity was shown. In the macula densa, the distal convoluted tubule and the collecting duct, very weak activity was observed in a few segments. Below the demarcation between the outer stripe and the inner stripe of the medulla, no enzyme activity was noticed. This is the first description of the exact tubular localizations of kallikrein-like enzyme activity in the nephron.