Adrenaline, also called epinephrine, is a hormone secreted by your adrenal glands, which sit on top of each of your kidneys. Once released by these glands, adrenaline produces a variety of effects on your body, including increases in your heart rate. These effects are triggered through interactions with certain portals on the surfaces of your cells called adrenergic receptors.
When you experience emotional stress or encounter a physically dangerous situation, your body prepares itself for prompt action by triggering your "fight-or-flight" response. This response begins in a region of your brain called the hypothalamus, which sounds the alarm and triggers increased production of adrenaline in your adrenal glands. These glands also increase the production of another hormone called cortisol. While cortisol suppresses nonessential activity and prepares your body for damage repair, adrenaline speeds up your heart rate, increases your energy supplies and raises your blood pressure.
Adrenaline's Heart Effects
Adrenaline in your bloodstream achieves its effects on your heart rate by stimulating the adrenergic receptors on cells throughout your heart tissue. Once stimulated, these receptors pass the fight-or-flight message to a specialized type of protein called a G-protein. In turn, G-proteins stimulate other substances inside your cells that trigger a cascading alert effect. The overall result of this process is an increase in your heart rate, as well as an increase in the force of each individual heart contraction.
Excessive Adrenalin Production
Under normal circumstances, your body will limit your fight-or-flight response to times of genuine emergency and return to normal function when appropriate. However, if your fight-or-flight response is triggered repeatedly or stays active long-term, the resulting increase in your blood levels of adrenaline and cortisol can significantly disrupt normal functional processes throughout your body. In addition to heart disease, potential consequences of this disruption include obesity, depression, sleep disturbances, worsening of existing skin conditions, digestion problems and memory impairment.
Adrenaline in your bloodstream also triggers the relaxation of smooth muscle cells throughout your body. When you experience significant physical or emotional stress, your adrenal gland produces two other hormones, called norepinephrine and dopamine, in addition to adrenaline and cortisol. Along with adrenaline, norepinephrine and dopamine belong to a class of substances called catecholamines. Your doctor may test your blood or urine for the presence of excessive catecholamines if you have high blood pressure or a tumor called a pheochromocytoma, which is known to abnormally increase levels of both adrenaline and norepinephrine.