How does vascular smooth muscle differ from other smooth muscle in terms of innervation?

From the Guidelines

Vascular smooth muscle differs from other smooth muscle in its unique dual innervation by both sympathetic and parasympathetic divisions of the autonomic nervous system, allowing for precise control of blood vessel diameter and blood flow. This is in contrast to other smooth muscle tissues, such as those in the gastrointestinal tract, which receive predominant innervation from one autonomic division, with parasympathetic innervation being both excitatory and inhibitory, and sympathetic input being generally inhibitory 1. The dual innervation of vascular smooth muscle enables the cardiovascular system to rapidly adjust blood flow to different organs based on physiological demands. Sympathetic stimulation typically causes vasoconstriction through norepinephrine release acting on alpha-adrenergic receptors, while parasympathetic stimulation generally promotes vasodilation through acetylcholine release.

Some key features of vascular smooth muscle innervation include:

• Dual innervation by sympathetic and parasympathetic divisions of the autonomic nervous system
• Regional specialization, with different blood vessels showing varying sensitivities to neural and hormonal control
• Response to local metabolic factors and endothelium-derived substances like nitric oxide, creating a complex regulatory system that integrates neural, hormonal, and local control mechanisms to maintain appropriate blood pressure and tissue perfusion throughout the body.

It's worth noting that the study by 1 focuses on the management strategies for gastrointestinal, erectile, bladder, and sudomotor dysfunction in patients with diabetes, and while it provides insight into the autonomic nervous system's role in modulating smooth muscle function, it does not directly address vascular smooth muscle innervation. However, the principles of autonomic nervous system control of smooth muscle function can be applied to understand the unique characteristics of vascular smooth muscle innervation.

From the Research

Vascular Smooth Muscle Innervation

• Vascular smooth muscle differs from other smooth muscle in terms of innervation, with a unique interaction between sympathetic nerve innervation and vascular smooth muscle cells (VSMCs) playing a major role in regulating arteriolar vasoconstriction, vascular resistance, and blood pressure 2.
• The sympathetic nervous system has a trophic influence on vascular smooth muscle, and its absence can lead to a decrease in response to noradrenaline in renal hypertensive rabbits 3.
• Vascular smooth muscle is activated through two major systems: one involving the influx of calcium through potential-sensitive channels, and the other involving the entry of calcium through agonist-controlled channels and its mobilization from within the cell 4.
• The tone of resistance vessels depends on a balance between the potential-sensitive and agonist-controlled systems, with an increased contribution to resistance vessel tone from the potential-sensitive system observed in primary hypertension 4.

Mechanisms of Vascular Smooth Muscle Contraction

• Vascular smooth muscle contraction is triggered by an increase in intracellular free calcium concentration ([Ca2+]i), promoting actin-myosin cross-bridge formation 5.
• Contraction is also regulated by calcium-independent mechanisms involving RhoA-Rho kinase, protein Kinase C, and mitogen-activated protein kinase signalling, reactive oxygen species, and reorganization of the actin cytoskeleton 5.
• The interaction between pannexin 1 and caveolin-1 in smooth muscle can regulate blood pressure, with genetic deletion of caveolin-1 significantly blunting adrenergic-stimulated ATP release and vasoconstriction 2.

Comparison to Other Smooth Muscle

• Vascular smooth muscle differs from other smooth muscle in its response to agents that selectively inhibit the two activation systems, with human veins, muscular arteries, and resistance vessels showing differing patterns of response 4.
• The unique interaction between sympathetic nerve innervation and VSMCs in vascular smooth muscle is not observed in other types of smooth muscle, highlighting the distinct characteristics of vascular smooth muscle innervation 2.