Acute limb ischemia does not facilitate but inhibits norepinephrine release from muscle sympathetic nerve endings in anesthetized rabbit.

Although myocardial ischemia is associated with regional cardiac sympathetic nerve deterioration, it remains unknown whether acute hindlimb ischemia impairs muscle sympathetic nerve function. In the study presented here we implanted dialysis probes in the adductor muscle of anesthetized rabbits and measured dialysate norepinephrine levels as an index of muscle sympathetic nerve activity. Acute hindlimb ischemia was induced by injection of microspheres and occlusion of the common iliac artery. Dialysate norepinephrine levels decreased from 19.3 +/- 3.5 pg/ml at control to 9.4 +/- 3.7 pg/ml at 30 min of ischemia and further to 1.7 +/- 0.2 pg/ml at 75 min of ischemia. During acute hindlimb ischemia, baroreflex (bilateral carotid occlusion) and high potassium level-induced norepinephrine response was inhibited, but tyramine-induced norepinephrine response was preserved. In conclusion, acute hindlimb ischemia caused decreases in dialysate norepinephrine levels. This reduction may be mediated by an impairment of axonal conduction and/or of norepinephrine releasing function at skeletal muscle sympathetic nerve endings.