Intrarenal infusion of bradykinin elicits a pressor response in conscious rats via a B2-receptor mechanism

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Abstract
Bradykinin (BK) is a peptide known to activate afferent nerve fibers from the kidney and elicit reflex changes in the cardiovascular system. The present study was specifically designed to test the hypothesis that bradykinin B2 receptors mediated the pressor responses elicited during intrarenal bradykinin administration. Pulsed Doppler flow probes were positioned around the left renal artery to measure renal blood flow (RBF). A catheter, to permit selective intrarenal administration of BK, was advanced into the proximal left renal artery. The femoral artery was cannulated to measure mean arterial pressure (MAP). MAP, heart rate (HR), and RBF were recorded from conscious unrestrained rats while five-point cumulative dose-response curves during an intrarenal infusion of BK (5-80 µg·kg-1·min-1) were constructed. Intrarenal infusion of BK elicited dose-dependent increases in MAP (maximum pressor response, 26 ± 3 mmHg), accompanied by a significant tachycardia (130 ± 18 beats/min) and a 28% increase in RBF. Ganglionic blockade abolished the BK-induced increases in MAP (maximum response, -6 ± 5 mmHg), HR (maximum response 31 ± 14 beats/min), and RBF (maximum response, 7 ± 2%). Selective intrarenal B2-receptor blockade with HOE-140 (50 µg/kg intrarenal bolus) abolished the increases in MAP and HR observed during intrarenal infusion of BK (maximum MAP response, -2 ± 3 mmHg; maximum HR response, 15 ± 11 beats/min). Similarly, the increases in RBF were prevented after HOE-140 treatment. In fact, after HOE-140, intrarenal BK produced a significant decrease in RBF (22%) at the highest dose of BK. Results from this study show that the cardiovascular responses elicited by intrarenal BK are mediated predominantly via a B2-receptor mechanism.Key words: bradykinin, blood pressure, renal hemodynamics, B2 receptors, autonomic nervous system.