[Biological regulation by the kallikrein-kinin system: a study with a kininogen-deficient rat strain]

It is well known that the kallikrein-kinin system expresses potent biological activities through its final product, bradykinin. However, bradykinin has an extremely short half life in biological fluids, so that it is difficult to quantitate the amount of bradykinin released in relevant pathological samples. Therefore investigators have attempted to prove its involvement or importance by measuring the precursor proteins, such as prekallikrein, kininogens, and glandular kallikreins. In this review, I would like to focus the discussion on a study of the kallikrein-kinin system in B/N Katholiek rats, a strain that has a congenital deficiency in plasma high molecular weight and low molecular weight kininogens. When experimental inflammation induced in the mutant deficient rats are compared to that induced in the normal rats (B/N-Kitasato), there was a significant difference; i.e., the deficient rats showed less swelling in the carrageenin-induced paw edema and less exudate accumulation in carrageenin-induced rat pleurisy. These results indicate that bradykinin may be released from kininogens and it may cause exudate formation in above inflammation. Furthermore, when experimental hypertension was induced by DOCA-salt loading, the blood pressure of the deficient rats rose faster than that of the normal rats. From the above findings, it is concluded that the plasma kallikrein-kinin system could be an important regulatory system in body defense mechanisms such as inflammation and blood pressure control.