Demonstration of high-molecular-weight kininogen in kininogen-deficient rat kidneys

Brown Norway Katholiek (B/N-Ka) is a mutant rat strain deficient in plasma high-molecular-weight (HK) and low-molecular-weight kininogen (LK). It has been reported that the deficiency, caused by defective secretion of HK and LK by the liver, is associated with a point mutation of alanine (163) to threonine in the common heavy chain. In this report we demonstrate by specific radioimmunoassay that the amount of immunoreactive HK antigen in the B/N-Ka kidney was almost the same as that found in the normal Brown Norway rat (Brown Norway Kitasato, B/N-Ki). HK antigen in the kidneys of both strains was immunohistochemically localized at distal tubules with similar intensity in both strains. Among the subcellular fractions of the kidney homogenates, HK antigen was predominantly found in the microsomal fraction of both strains. To see whether this HK antigen is derived from plasma HK or is synthesized in the kidneys, we examined uptake of HK by the tubular cells after incubation with 125I-HK. Only 0.6% of the radioactivity of added 125I-HK was found in the tubular cells of both strains after a 60-min incubation. Messages of HK mRNA from both strains of rats were visualized by PCR at almost the same intensity. These results suggest that HK antigen found in the kidney may be derived mainly from biosynthesis in the kidney itself and partly from uptake of HK from blood. There was no difference in these features of HK between the kidneys of the deficient and the normal B/N rats.