Adrenaline and norepinephrine in the blood

Reference concentrations in blood plasma: adrenaline - 112-658 pg / ml;norepinephrine - less than 10 pg / ml.

Adrenaline is the hormone of the adrenal medulla. From the adrenal medulla it enters the bloodstream and acts on the cells of distant organs. Its content in the blood depends on the tone of the sympathetic system. In hepatocytes, epinephrine stimulates the breakdown of glycogen and thereby increases the glucose level in the blood. In adipose tissue adrenaline activates lipase and the process of cleavage of TG.Adrenaline also activates glycogenolysis in muscle cells. It increases cardiac contractions and increases their frequency, increases blood pressure mainly due to systolic. Adrenaline expands the vessels of the muscles and heart and narrows the vessels of the skin, mucous membranes and abdominal cavity organs. He plays a big role in the reaction of the body to stressful situations. Under its influence, the production of ACTH increases, and consequently, of corticosteroids. It increases the sensitivity of the thyroid gland to the action of TSH.The

concentration of epinephrine in the blood characterizes the humoral part of the sympathetic nervous system.

In contrast to adrenaline, norepinephrine enters the blood plasma mainly from sympathetic nerve endings( most of it is again absorbed by neurons, and 10-20% gets into the blood).Only a very small part of norepinephrine of blood is formed in the adrenal medulla. The action of norepinephrine is associated with a predominant effect on a-adrenergic receptors, while adrenaline acts on a-and p-adrenergic receptors. The concentration of norepinephrine in the blood characterizes the activity of neurons in the sympathetic nervous system.

The definition of epinephrine and norepinephrine is used in clinical practice mainly for the diagnosis of pheochromocytoma and differential diagnosis of arterial hypertension.

In patients with pheochromocytoma, the concentration of catecholamines in the blood increases by 10-100 times. The correspondence between the size of the tumor, the concentration of catecholamines in the blood and the clinical picture does not exist. Small tumors can synthesize and secrete large amounts of catecholamines into the blood, whereas large tumors metabolize catecholamines into their own tissue and secrete only a small fraction of them. Most pheochromocytomas secrete norepinephrine in the blood first. With hypertension, the concentrations of catecholamine in the blood are at the upper limit of the norm or increased by a factor of 1.5-2.If in a state of rest the concentration of catecholamines in the blood plasma exceeds 2000 μg / l, then the presence of pheochromocytoma should be suspected. Concentrations of 550-2000 μg / l should raise doubts about the presence of the tumor, in such cases additional studies, in particular clonidine test, are necessary. The test is based on the ability of clonidine to reduce the tone of the sympathetic nervous system and thus reduce the concentration of norepinephrine in the blood. Blood is taken twice: on an empty stomach and 3 hours after oral intake of 0.3 mg clonidine. In patients with pheochromocytoma, the concentration of norepinephrine after taking the drug does not change significantly or decreases by less than 50% of the baseline, in patients with arterial hypertension of a different origin and in healthy people, the concentration of noradrenaline decreases by more than 50%.

It should be remembered that with adrenal pheochromocytoma, the concentration of adrenaline and norepinephrine in the blood increases, whereas the intravenous pheochromocytomas usually cause an increase in the content of only norepinephrine.

The study of the concentration of catecholamines in the blood and their excretion in urine is important not only for the diagnosis of pheochromocytoma, but also for monitoring the effectiveness of treatment. Radical tumor removal is accompanied by normalization of excretion of these substances, and tumor recurrence leads to its repeated increase.

The sensitivity of the methods for determining the concentration of adrenaline and norepinephrine in the blood for the diagnosis of pheochromocytoma is lower than for their determination in urine.