Norepinephrine in the bloodstream

Norepinephrine [NE], although it can be classified under the broad umbrella of hormones, has a greater role to play as a neurotransmitter - so, as far as muscle is concerned, it is released from the adrenergic [sympathetic] nerve supply to the smooth muscle in the arterioles. When an impulse travels down the postganglionic neurone [this would start off after a synapse in the paravertebtral sympathetic chain either side of the spinal column, where the neurotransmitter is acetylcholine] and reaches the end of this [second] neurone, at this synapse, which lies on the arteriolar smooth muscle, NE is released and acts on the alpha adrenergic receptors to cause contraction of this [circular] smooth muscle, so that the arterioles constrict.

Action of NE on beta-2 receptors on the smooth muscle on muscular arterioles [i.e. arterioles that supply skeletal [striated] muscle], causes this smooth muscle to relax, causing dilatation, in order to increase blood flow [e.g. if a lion jumps in through your window, and you need to quickly make a move lol - it has been known to happen where I was brought up = Kenya!]

Having said that, depending what level you are studying at [not necessary to know at A level], beta-1 receptors are found mainly in the heart [mediate increased heart rate and force of contraction] and other important beta-2 receptors in the bronchiolar smooth muscle in the lungs [stimulation leads to bronchodilatation]

Hope this helps!
M.