Tissue kallikrein-binding protein reduces blood pressure in transgenic mice

The kallikrein-kinin system participates in blood pressure regulation. One of the kallikrein-kinin system components, kallikrein-binding protein, binds to tissue kallikrein and inhibits its activity in vitro. To investigate potential roles of rat kallikrein-binding protein (RKBP) in vivo, we have developed transgenic mice that express an RKBP gene under the control of the mouse metallothionein metal-responsive promoter. Expression of the transgene, RKBP, was detected in the liver, kidney, lung, heart, pancreas, salivary glands, spleen, brain, testis, and adrenal gland at the mRNA and protein levels. Systolic blood pressures of homozygous transgenic mice were 88.5 +/- 0.8 mm Hg (mean +/- S.E., n = 19, P < 0.001) for one line and 88.8 +/- 1.6 mm Hg (mean +/- S.E., n = 19, P < 0.001) for another, as compared with 100.5 +/- 0.8 mm Hg (mean +/- S.E., n = 18) for control mice. Direct blood pressure measurements of these transgenic mice through an arterial cannula showed similar reductions of blood pressure. Intravenous injection of purified RKBP into mice via a catheter produced a dose-dependent reduction of the mean arterial blood pressure. Our findings suggest that RKBP may function as a vasodilator in vivo, independent of regulating the activity of tissue kallikrein.