Characterization of elements of the kallikrein-kinin system in rainbow trout (Salmo gairdneri)

Elements of kallikrein-kinin system (KKS) are found in anamniotic vertebrates, however, research has failed to substantiate the presence of a KKS in these animals. This research was conducted to verify the presence of elements of the KKS in rainbow trout. Trout branchial angiotensin-converting enzyme (ACE, kininase II) was similar to mammalian ACE in many physical, chemical and kinetic parameters. Angiotensin-converting enzyme-like activity (ACELA) was also demonstrated in the most primitive vertebrates. ACELA was consistently found in vertebrate respiratory tissues and was prevalent in salt and water exchanging organs. 3H-bradykinin, perfused through the trout gill was not metabolized, as demonstrated by high voltage paper electrophoresis. However, trout gills extracted and retained approximately 40% of the 3H-bradykinin perfused into the branchial vasculature. Gill tissue homogenates metabolized both 3H-bradykinin and the vasoactive substance produced by incubating trout plasma with glandular kallikrein