Chronic femoral arterial ligation augments group III muscle afferent responses to static contraction

The exercise pressor reflex is evoked in part by stimulation of group III afferents in freely perfused hindlimb muscles. In addition, the reflex is augmented by ligation of the femoral artery 72 hours before the start of the experiment. We, therefore, hypothesized that femoral arterial ligation augmented the responses of group III muscle afferents to static contraction. In barbiturate anesthetized rats, we recorded the impulse activity of group III afferents with endings in the triceps surae muscles. The responses to static contraction of group III afferents in rats whose hindlimb muscles were freely perfused (n=5) were compared with those from rats whose femoral arteries were ligated 72 hours before the start of the experiment (n=4). We found that static contraction for 60 seconds increased the firing rate of 2 of the 5 group III afferents tested from freely perfused muscles, whereas static contraction increased the firing rate of 4 of the 4 group III afferents tested from the 72 hour ligated muscles (P<0.05). Tension time indices between groups were not different (P=0.39). Our findings suggest that the augmented pressor response to static contraction in rats whose femoral arteries were ligated 72 hours before the start of the experiment is in part due to an augmented group III muscle afferent response to static contraction.