The kallikrein-kinin system in the kidney.

To understand the role of the kallikrein-kinin system in the kidney all components of the system and their localization need to be considered. About half the kallikrein in urine occurs as the proenzyme which arises in the distal tubule. Kinins are formed in the distal tubule and collecting duct from urokinnogen which is found throughout the tubule. Urine contains about twice as much lysyl-brandykinin as bradykinin. A third kinin, methionyl-lysyl-bradykinin, also can occur in urine. It is probably produced by uropepsin as the kinin is largely formed in acidified urine and its formation is inhibited by pepstatin. The significance of the three kinins is unknown. Kinins are normally slowly (few hours) destroyed in urine. The importance of kallikrein, urokinogen and kininases in regulating the level of kinins needs to be determined.