Long-acting alpha 1-adrenoceptive sympathomimetic agent suppresses sympathetic outflow to muscles in humans

To clarify the effect of a long-acting selective α 1 -adrenoceptive sympathomimetic agent on sympathetic outflow to muscles (muscle sympathetic activity, MSA) in humans, 5 mg of midodrine hydrochloride was injected intravenously in ten healthy male subjects aged 19–25. Spontaneous MSA was significantly suppressed as well as plasma norepinephrine level without changing heart rate, or systemic blood pressure. The suppression continued for more than 90 min. and this is supposed to be due to negative feedback action on the baroreflex loop. The absence of significant changes in heart rate or systemic blood pressure in healthy subjects suggests that hemodynamic homeostasis is maintained by reducing the MSA in response to a long-acting sympathomimetic agent, like midodrine hydrochloride, which constricts peripheral vessels directly.