A Proposed Differentiated Neuro-Effector Organization in Muscle Resistance Vessels

Abstract

The extent of vasodilatation in skeletal muscle, produced by standardized activations of the sympathetic cholinergic vasodilator fibers from the hypothalamic "defence area", has been studied during various levels of concomitant vasoconstrictor fiber activity and compared with the effects of standardized close arterial injections of acetylcholine. It was found that the dilator response to hypothalamic stimulation, which was pronounced when the vasoconstrictor fiber activity was inhibited, was more or less completely suppressed when the constrictor activity was enhanced, despite the fact that acetylcholine produced essentially the same degree of vasodilatation in the 2 situations. Based on these data and recent observations of other authors concerning the distribution of adrenergic fiber terminals to the smooth muscles of the resistance vessels, a hypothesis is advanced implying that the sympathetic nerve fibers and vascular smooth muscles are differentiated into a dual neuro-effector system in skeletal muscles. According to this hypothesis the smooth muscles in the resistance vessels are arranged in 2 principal, functionally different sheaths, one inner, myogenically active layer, receiving the main part of the cholinergic vasodilator fibers, surrounded by an outer sheath, where the smooth muscles essentially lack myogenic activity but are subordinated to a strict adrenergic vasoconstrictor fiber control. Some implications of the data presented and the hypothesis advanced are discussed.