Noradrenaline receptors
The specific receptors for norepinephrine and adrenaline are called adrenoceptors. The two messenger substances act at two different receptor subtypes. On the one hand, the alpha receptors are stimulated and on the other hand the beta receptors are activated.
Alpha-1-receptors are mostly located on the walls of the blood vessels, which ensure the supply of the kidneys and the gastrointestinal tract. If these receptors are stimulated, this causes a narrowing of the blood vessels (vasoconstriction), which results in an increase in arterial blood pressure. Beta-1 receptors are located in the heart; their activation leads to an increase in heart strength and heart rate.
It also improves the transmission of electrical excitation within the heart, which leads to the contraction of muscle cells. These effects together result in more efficient cardiac activity. The blood vessels in the gastrointestinal tract mainly express beta-2 receptors, which, when activated, leads to a dilation of the vessels (vasodilation) and thus improves the blood supply to the organs. The receptors are also found in the bronchi, where they cause an increase in diameter (bronchodilation).
Elevated norepinephrine levels
To evaluate individual norepinephrine levels, the amount of norepinephrine in the patient’s urine is determined. For this purpose, the patient first collects his excreted urine over a period of 24 hours, which is used completely for measurement. The results are interpreted in relation to the known reference values.
For a healthy adult, these are in the range of 23-105 μg or 135-620 nmol per day. An increased excretion of norepinephrine indicates an increase of the norepinephrine level in the blood, which can be caused by various factors. On the one hand, this can be the result of a hormone-producing tumor of the adrenal medulla, a pheochromocytoma.These are benign in 85% of cases and produce mostly uncontrolled noradrenaline and adrenaline, and rarely dopamine.
Furthermore, a neuroblastoma, a malignant tumor of the nerve cells of the adrenergic system, can lead to an increased production of catecholamines. Among the more common causes of elevated norepinephrine levels are high blood pressure and prolonged stress, although no difference can be found between psychological stress and excessive physical exertion. However, this stress-related increase in catecholamines is not permanently tolerated by the body, which results in a feeling of physical exhaustion.
