Bradykinin receptor blockade reduces sympathetic nerve response to muscle contraction in rats with ischemic heart failure

Previous animal and human studies have suggested that a muscle reflex engaged during contraction leads to heightened levels of sympathetic activity in congestive heart failure (CHF). The present experiment was designed to test the role for bradykinin, which is produced within contracting skeletal muscle and contributes to the muscle reflex through its action on kinin B2 receptors located on the endings of thin fiber muscle afferents. CHF was induced in rats by myocardial infarction (MI) after coronary artery ligation. Echocardiography was performed to determine fractional shortening (FS), an index of the left ventricular function. In the decerebrate rats, we examined renal sympathetic nerve activity (RSNA) during 1 min intermittent (1 to 4 s stimulation to relaxation) contraction of left triceps surae muscles. RSNA responded synchronously as tension was developed, and the response was significantly (P < 0.05) greater in MI rats [+39 ± 9% s^-1 (integrated RSNA over time); n = 16] with 20 ± 2% of FS than that in control healthy rats (+19 ± 2% s^-1; n = 16) with 49 ± 2% of FS. Tension development did not differ significantly between the two groups of rats. Thirty minutes after intra-arterial injection into the hindlimb circulation of the kinin B2 receptor antagonist, HOE-140 (2 μg/kg), the RSNA response to contraction was significantly reduced in the MI rats (+26 ± 7% s ^-1) but not in the control rats (+17 ± 2% s^-1). These data suggest that bradykinin within contracting muscle is part of the exaggerated muscle reflex seen in CHF.