Reflex responses in plasma catecholamines caused by static contraction of skeletal muscle

To examine a hypothesis of whether static muscle contraction produces a rel ease of catecholamines from the adrenal medulla via reflex stimulation of p reganglionic adrenal sympathetic nerve activity induced by receptors in the contracting muscle, we compared the reflex responses in a concentration of epinephrine (Ep) and norepinephrine (NEp) in arterial plasma during static contraction and during a mechanical stretch of the hindlimb triceps surae muscle in anesthetized cats. Static contraction was evoked by electrically stimulating the peripheral ends of the cut L-7 and S-1 ventral roots at 20 or 40 Hz. Mean arterial pressure (MAP) and heart rate (HR) increased 23 +/- 3.1 mmHg and 19 +/- 4.3 beats/min during static contraction. Ep in arteria l plasma increased 0.18 +/- 0.072 ng/ml over the control of 0.14 +/- 0.051 ng/ml within 1 min from the onset of static contraction, and NEp increased 0.47 +/- 0.087ng/ml over the control of 0.71 +/- 0.108 ng/ml. Following a n euromuscular blockade, although the same ventral root stimulation failed to produce the cardiovascular and plasma catecholamine responses, the mechani cal stretch of the muscle increased MAP, HR, and plasma Ep, but not plasma NEp. With bilateral adrenalectomy, the baseline Ep became negligible (0.012 +/- 0.001 ng/ml) and the baseline NEp was lowered to 0.52 +/- 0.109 ng/ml. Neither static contraction nor mechanical stretch produced significant res ponses in plasma Ep and NEp following the adrenalectomy. These results sugg est that static muscle contraction augments preganglionic adrenal sympathet ic nerve activity, which in turn secretes epinephrine from the adrenal medu lla into plasma. A muscle mechanoreflex from the contracting muscle may pla y a role in stimulation of the adrenal sympathetic nerve activity.