Background:

Bradykinin (BK) is an endogenously produced active peptide that causes vasodilation. However, its effect on the renal microvasculature is not well described when introduced as an exogenous compound. This study evaluated the effects of BK on renal cortical and medullary blood perfusion and investigated whether the effect of BK is similar when given locally into the renal medulla or systematically with the intravenous route (IV).

Materials and Methods:

Four groups (n=7) of male Wistar rats (250-300 g) were anaesthetised with an I.P injection of 1 ml chloralose/urethane, 16.5/250 mg/ml. The right femoral vein was cannulated for infusion of saline (154mM NaCl), BK (50μg/kg/min) at 3ml/h and supplemental doses of anaesthetic. The right femoral artery was cannulated to measure blood pressure (BP). The left kidney was exposed via a flank incision, and a small cannula was inserted 4.5mm into the kidney for intramedullary (i.m) infusion of saline or BK at 0.6-1.0 ml/h. Two Laser-Doppler microprobes (each 0.5 mm diameter) were inserted 1.5 and 4.0 mm into the kidney to measure cortical and medullary blood perfusion, respectively (100 perfusion units (PU) = 1 V). After 90 min, baseline measurements were taken, and then either vehicle or BK were infused i.m or IV for 60 min. At the end of the experiments, the animals were killed with an anaesthetic overdose. Data ± SEM were subjected to the Student's t-test, and significance was taken at P<0.05.

Results:

The baseline levels of BP were 95±8 mmHg, Heart Rates (HR) were 335±10 BPM, CP was 138±7 PU, and MP was 57±5 PU. Administration of bradykinin i.m significantly increased MP and CP (18 ± 6% and 33 ± 9%, respectively, P<0.05.). BK had no effect on BP and HR when given locally. IV Infusion of BK resulted in a significant increase in CP (23 ± 6%, P<0.05.) and a decrease in MAP (15 ± 6%, P<0.05.), but had no effect on MP and HR.

Conclusion:

BK, when given locally, dilates renal blood vessels, mediating an increase in CP and MP. When given systematically, the effect of bradykinin was less on the renal microvasculature and had no impact on the MP. These data indicate that the BK has a more significant effect on the medullary microvasculature when given locally. Further research is suggested to understand the action of BK on renal microvasculature and the involvement of the free radicals such as superoxide anion and nitric oxide.