Noradrenaline, or norepinephrine, is a hormone made in the adrenal gland. It is used as a chemical signal between cells of the sympathetic nervous system, a branch of the nervous system in charge of alertness, hyperactivity and quick responses. Noradrenaline exhibits effects on the heart by binding to certain receptors in the heart and in the blood vessels.
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Increase in Heart Rate
Noradrenaline interacts with beta receptors found on pacemaker cells in the heart; it stimulates the pacemaker cells, thereby increasing the rate at which they generate electrical charges. Each charge released from pacemaker cells cause the heart to contract. Noradrenaline increases heart rate initially but this effect is minimized by its effect on blood vessel.
Decrease in Heart Rate
Heart rate is also decreased with noradrenaline release but is a delayed effect; noradrenaline interacts with alpha receptors in the arteries, thereby causing constriction of blood vessel. Blood vessel constriction, triggers a reflex pathway that causes the heart rate to slow down.
The effect of noradrenaline on heart rate is minimized by beta blockers. A person may need beta blockers for the treatment of hypertension, rapid heart rater or heart failure. Alpha receptor blockers reduce the constrictive effects of noradrenaline on blood vessels but allows the increase in heart rate.