Differential regulation of kallikrein, kininogen, and kallikrein- binding protein in arterial hypertensive rats

This study was designed to determine whether the kallikrein-kinin system exerts a protective action in hypertension induced by chronic inhibition of nitric oxide synthase. N(ω)-nitro-L-arginine methyl ester (L-NAME, 40 mg/100 ml water) was given orally to Sprague-Dawley rats, while controls received regular tap water. Hepatic kininogen mRNA levels in the L-NAME-treated group were 2.9- and 2.5-fold higher at 3 and 4 wk, respectively, compared with control rats, whereas kallikrein-binding protein (KBP) mRNA levels were 82% and 45% of the values found in control rats at 3 and 4 wk, respectively. There was no significant change in hepatic α ₁-antitrypsin mRNA levels under the same conditions. At 3 and 4 wk post L-NAME treatment, renal kallikrein mRNA levels were 2.5- and 3.4-fold higher than in controls, whereas renal β- actin mRNA levels were similar between groups. Changes in the transcript levels of renal kallikrein, kininogen, and KBP were consistent with their protein levels. Immunoreactive total kininogen and low-M(r) kininogen levels in sera and tissue kallikrein levels in kidney were significantly higher in the L-NAME-treated group, whereas KBP levels in the circulation were lower compared with controls. Systolic blood pressure was increased by 58 ± 4 mmHg after 4 wk of L-NAME treatment. This effect was enhanced in rats given L- NAME in combination with HOE-140, a bradykinin B ₂-receptor antagonist, at the dose of 100 μg/day ip (79 ± 5 vs. 58 ± 4 mmHg, P <0.05). This difference was confirmed by direct measurement of mean blood pressure (MBP). An intra-arterial bolus injection of 200 ng bradykinin significantly decreased MBP of L-NAME-treated rats, and this effect was blunted in the group treated with the bradykinin antagonist (-29 ± 3 vs. -9 ± 2 mmHg, P <0.01). These results suggest that enhanced kallikrein and kininogen synthesis may have a protective role against the cardiovascular effects induced by chronic inhibition of nitric oxide synthesis.