Cyclooxygenase products sensitize group III and IV muscle afferents to dynamic exercise

Abstract

Cyclooxygenase products accumulate in statically contracting muscles to stimulate group III and IV afferents. The role played by these products in stimulating muscle afferents during dynamic exercise is unknown. Therefore, in decerebrate cats, we recorded the responses of 15 group III and 10 group IV triceps surae muscle afferents to dynamic exercise, evoked by stimulation of the mesencephalic locomotor region. Each afferent was tested while the muscles were freely-perfused and while the circulation to the muscles was occluded. The increases in group III and IV afferent activity during dynamic exercise while the circulation to the muscles was occluded were greater than those during exercise while the muscles were freely perfused. Indomethacin (5 mg/kg; i.v.) reduced the responses to exercise of group III afferents by 42% during circulatory occlusion and by 29% while the muscles were freely perfused. Likewise, indomethacin reduced the responses to exercise of group IV afferents by 34% during circulatory occlusion and by 18% while the muscles were freely perfused. Before indomethacin, group IV, but not group III activity, was significantly higher during post exercise circulatory occlusion than the activity during rest. After indomethacin, however, group IV activity during post exercise circulatory occlusion was not significantly different than the activity during rest. These data suggest that cyclooxygenase products play a role both in sensitizing group III and IV afferents during exercise and in stimulating group IV afferents during post exercise circulatory occlusion. Supported by NIH HL 30710