Is vascular smooth muscle subject to the sympathetic nervous system?

From the Guidelines

Yes, vascular smooth muscle is subject to the sympathetic nervous system. The sympathetic nervous system directly innervates blood vessels throughout the body, releasing norepinephrine which binds to alpha-1 adrenergic receptors on vascular smooth muscle cells, as noted in the context of cocaine use and its effects on the cardiovascular system 1. This activation causes vasoconstriction in most blood vessels, increasing peripheral resistance and blood pressure. The degree of sympathetic control varies by location - vessels in the skin, splanchnic region, and kidneys are heavily innervated and respond strongly to sympathetic stimulation, while cerebral and coronary vessels have less sympathetic innervation.

Key Points

• The sympathetic nervous system plays a crucial role in maintaining blood pressure during position changes, responding to stress, and redirecting blood flow during exercise.
• Medications that target this system include alpha-blockers like prazosin which reduce sympathetic vasoconstriction, and beta-blockers like metoprolol which primarily affect cardiac output but can also influence vascular tone through beta-2 receptors in some vessels.
• The action of cocaine, for example, blocks presynaptic reuptake of neurotransmitters such as norepinephrine and dopamine, leading to sympathetic activation and potential direct contractile effects on vascular smooth muscle 1.
• The management of conditions like hypertension and ischemic heart disease involves understanding the role of the sympathetic nervous system and its impact on vascular smooth muscle, as well as the use of appropriate medications to manage these conditions 1.

Clinical Implications

• Understanding the sympathetic nervous system's control over vascular smooth muscle is essential for managing various cardiovascular conditions, including hypertension and ischemic heart disease.
• The use of sympatholytic drugs, such as alpha-blockers, can be beneficial in certain conditions, like urinary outflow obstruction, by indirectly dilating prostatic and urinary sphincter smooth muscle and lowering blood pressure 1.
• The recognition of the sympathetic nervous system's role in cocaine-induced cardiovascular effects is critical for the appropriate management of patients with cocaine-associated acute coronary syndromes, including the cautious use of beta blockers and the preference for combination alpha and beta blockade along with vasodilators 1.

From the Research

Vascular Smooth Muscle and the Sympathetic Nervous System

• Vascular smooth muscle is indeed subject to the sympathetic nervous system, as evidenced by various studies 2, 3, 4, 5, 6.
• The sympathetic nervous system plays a key role in vascular smooth muscle function, with epinephrine and norepinephrine stimulating vascular smooth muscle cells via delta and beta adrenergic receptors 3.
• The trophic influence of the sympathetic nervous system on vascular smooth muscle is essential for the integrity of the muscle and is pertinent to renal hypertension in the rabbit 2.
• Sympathetic innervation promotes vascular smooth muscle differentiation, as shown by increased expression of smooth muscle myosin and alpha-actin in innervated rat femoral and tail arteries 5.
• The sympathetic nervous system also stimulates vascular smooth muscle cells to retain their contractile phenotype, with studies suggesting that it promotes VSMCs' contractile gene expression and maintains VSMCs' functional phenotype 6.
• Alpha 1-receptor antagonists, such as urapidil and prazosin, have been shown to inhibit neointima formation in rat carotid arteries, highlighting the role of the sympathetic nervous system in vascular smooth muscle cell proliferation 4.