Bradykinin B2 receptor contributes to the exaggerated muscle mechanoreflex in rats with femoral artery occlusion

Static muscle contraction activates the exercise pressor reflex, which in turn increases sympathetic nerve activity (SNA) and blood pressure (BP). Bradykinin (BK) is considered as a muscle metabolite responsible for modulation of the sympathetic and cardiovascular responses to muscle contraction. Prior studies have suggested that kinin B2 receptor mediates the effects of BK on the reflex SNA and BP responses during stimulation of skeletal muscle afferents. In patients with peripheral artery disease and a rat model with femoral artery ligation, amplified SNA and BP responses to static exercise were observed. This dysfunction of the exercise pressor reflex has previously been shown to be mediated, in part, by muscle mechanoreflex overactivity. Thus, in this report, we determined whether kinin B2 receptor contributes to the augmented mechanoreflex activity in rats with 24 h of femoral artery occlusion. First, Western blot analysis was used to examine protein expression of B2 receptors in dorsal root ganglion tissues of control limbs and ligated limbs. Our data show that B2 receptor displays significant overexpression in ligated limbs as compared with control limbs (optical density: 0.94 ± 0.02 in control and 1.87 ± 0.08 after ligation, P < 0.05 vs. control; n = 6 in each group). Second, mechanoreflex was evoked by muscle stretch and the reflex renal SNA (RSNA) and mean arterial pressure (MAP) responses to muscle stretch were examined after HOE-140, a B2 receptors blocker, was injected into the arterial blood supply of the hindlimb muscles. The results demonstrate that the stretch-evoked reflex responses were attenuated by administration of HOE-140 in control rats and ligated rats; however, the attenuating effects of HOE-140 were significantly greater in ligated rats, i.e., after 5 μg/kg of HOE-140 RSNA and MAP responses evoked by 0.5 kg of muscle tension were attenuated by 43% and 25% in control vs. 54% and 34% in ligation ( P < 0.05 vs. control group; n = 11 in each group). In contrast, there was no significant difference in B1 receptor expression in both experimental groups, and arterial injection of R-715, a B1 receptors blocker, had no significant effects on RSNA and MAP responses evoked by muscle stretch. Accordingly, results obtained from this study support our hypothesis that heightened kinin B2 receptor expression in the sensory nerves contributes to the exaggerated muscle mechanoreflex in rats with femoral artery occlusion.