Blockade of B2 receptors attenuates the responses of group III afferents to static contraction.

Recent evidence has been presented demonstrating that group III mechanoreceptors comprise an important part of the sensory arm of the exercise pressor reflex, which in turn functions to increase arterial blood flow to contracting skeletal muscles. Although group III afferents are stimulated by mechanical distortion of their receptive fields, they are also stimulated by bradykinin, which is produced by skeletal muscle when it contracts. Moreover, blockade of B (bradykinin)2 receptors has been shown to decrease the magnitude of the exercise pressor reflex. Nevertheless, the effect of blockade of B2 receptors on responses of group III afferents to contraction is not known. We therefore determined the effect of B2 receptor blockade with HOE 140 (40µg/kg) on the responses to both static and intermittent contraction of group III afferents with endings in the triceps surae muscle of decerebrated unanesthetized cats. We found that HOE 140 significantly attenuated (P=0.04) the responses of 14 group III afferents to static contraction, but did not significantly attenuate (P=0.16) the responses of 16 group III afferents to intermittent contraction. The attenuation induced by HOE 140 was present throughout the static contraction period, and led us to speculate that blockade of B2 receptors on the endings of group III afferents decreased their sensitivity to mechanical events occurring in the working muscles.