Activation of peripheral mu‐opioid receptor attenuates the augmented exercise pressor reflex seen in rats with chronic femoral artery occlusion

Abstract

The sensory arm of the exercise pressor reflex arc is comprised of group III and IV afferents. Recently, opioid receptors have been shown to be expressed on them. Although the stimulation of opioid receptors in the central nervous system has been shown to attenuate the exercise pressor reflex, the effect of stimulation of peripheral opioid receptors on the reflex is unknown. We therefore tested the hypothesis that activation of peripheral μ‐opioid receptors attenuates the reflex pressor response to static contraction in decerebrated rats. The pressor responses to static contraction were compared before and after injection of the μ‐opioid receptor agonist DAMGO into the abdominal aorta of rats in which one femoral artery was occluded 72 hours previously (n=8) and in other rats whose femoral arteries were freely perfused (n=8). The pressor response to contraction in rats whose femoral artery was ligated was attenuated by DAMGO (1 μg) from Δ 37 ± 4 mmHg to Δ 20 ± 4 mmHg (P<0.001). This inhibitory effect was antagonized by pretreatment with 100 μg of naloxone (Δ 29 ± 5 mmHg before and Δ29 ± 5 mmHg after, P = 0.9). In contrast, DAMGO had no effect on the pressor response to contraction in rats whose femoral arteries were freely perfused (Δ19 ± 4 mmHg before and Δ 21 ± 3 mmHg after, P = 0.9). We conclude that stimulation of peripheral μ‐opioid receptors attenuates the exercise pressor reflex in rats with “chronic” femoral arterial ligation.