How does sympathetic activation affect blood vessel diameter, leading to either vasodilation or vasoconstriction?

Sympathetic activation can cause blood vessels to either dilate (vasodilation) or constrict (vasoconstriction) by releasing neurotransmitters that bind to receptors on the blood vessel walls. When the sympathetic nervous system is activated, it releases norepinephrine, which can bind to alpha-adrenergic receptors on blood vessels, causing them to constrict and decrease blood flow. Alternatively, the release of epinephrine can bind to beta-adrenergic receptors, leading to vasodilation and an increase in blood flow.