Adrenomimetics are a group of medications, the result of which is associated with the stimulation of adrenoreceptors located in the internal organs and vascular walls. All adrenoreceptors are divided into several groups depending on localization, mediated effect and ability to form complexes with active substances. Excitatory alpha-adrenergic agonists act on alpha-adrenergic receptors, causing a specific response from the body.
What are alpha adrenergic receptors?
A1-adrenergic receptors are located on the surface membranes of cells, in the region of synapses, react to norepinephrine, which is secreted by the nerve endings of the postganglionic neurons of the sympathetic nervous system. They are localized in the arteries of small caliber. Excitation of receptors causes vascular spasm, hypertension, decreased permeability of the arterial wall, a decrease in the manifestations of inflammatory reactions in the body.
A2-adrenergic receptors are located outside the synapses and on the presynaptic cell membrane. React to the effects of norepinephrine and epinephrine. Excitation of receptors causes a reverse reaction, which is manifested by hypotension and relaxation of blood vessels.
General information on adrenergic agonists
Alpha and beta-adrenergic agonists, which independently bind to receptors sensitive to them and cause the effect of adrenaline or norepinephrine, are called direct-acting agents.
The result of the influence of drugs can also occur through indirect action, which is manifested by stimulation of the development of their own mediators, prevents their destruction, and contributes to an increase in concentration on nerve endings.
Adrenomimetics are prescribed in the following conditions:
- heart failure, severe hypotension, collapse, shock, cardiac arrest;
- bronchial asthma, bronchospasm;
- increased intraocular pressure;
- inflammatory diseases of the mucous membranes of the eyes and nose;
- hypoglycemic coma;
- local anesthesia.
Alpha adrenomimetics
The group of drugs includes selective (act on one type of receptor) and non-selective (excitation of A1 and A2 receptors) drugs. Non-selective alpha-adrenergic agonist is represented directly by norepinephrine, which stimulates beta-receptors.
Alpha-adrenergic agonists affecting the A1 receptors are anti-shock medications used for a sharp decrease in blood pressure. They can be used topically, causing narrowing of the arterioles, which is effective for glaucoma or allergic rhinitis. Famous drugs of the group:
- Midodrin
- Mesaton
- Ethylephrine.
Alpha-adrenergic agonists affecting a2 receptors are better known to the general public due to their widespread use. Popular representatives are Xylometazoline, Nazol, Sanorin, and Vizin. They are used in the treatment of inflammatory diseases of the eyes and nose (conjunctivitis, rhinitis, sinusitis).
The drugs are known for their vasoconstrictor effect, which eliminates nasal congestion. The use of funds should occur only under the supervision of a specialist, since prolonged uncontrolled administration can cause the development of drug resistance and atrophy of the mucous membrane.
Young children are also prescribed drugs containing alpha-adrenergic agonists. Drugs in this case have a lower concentration of the active substance. The same forms are used in the treatment of people suffering from diabetes mellitus and hypertension.
Alpha-adrenergic agonists that stimulate a2-receptors include centrally acting drugs (Methyldopa, Clonidine, Catapresan). Their action is as follows:
- antihypertensive effect;
- decreased heart rate;
- sedative effect;
- minor anesthesia;
- decrease in secretion of the lacrimal and salivary glands;
- decreased secretion of water in the small intestine.
Mesaton
Phenylephrine hydrochloride- based drug that causes high blood pressure. Its use requires precise dosage, since a reflex reduction in heart rate is possible. "Mesatone" increases the pressure gently compared to other drugs, but the effect is more lasting.
Indications for use of the product:
- arterial hypotension, collapse;
- preparation for surgery;
- vasomotor rhinitis ;
- local anesthesia;
- poisoning of various etiologies.
The need for immediate results requires intravenous administration. The drug is also injected into the muscle, subcutaneously, intranasally.
"Xylometazoline"
A drug having the active substance of the same name, which is part of "Galazolin", "Otrivin", "Xymelin", "For carrying". It is used in local therapy of acute infectious rhinitis, sinusitis, pollinosis, otitis media, in preparation for surgical or diagnostic interventions of the nasal cavity.
Available in the form of a spray, drops and gel for intranasal applications. The spray is allowed for use by children from the age of 12. It is prescribed with caution in the following conditions:
- angina pectoris;
- lactation period;
- thyroid disease;
- prostatic hyperplasia;
- diabetes;
- pregnancy.
"Clonidine"
The drug is an alpha-adrenergic agonist. The mechanism of action of Klofelin is based on the excitation of a2-adrenergic receptors, resulting in a decrease in pressure, the development of a slight analgesic and sedative effect.
It is widely used in various forms of hypertension, hypertensive crisis, to relieve an attack of glaucoma, in combination with other drugs for the treatment of drug and alcohol addiction.
"Clonidine" is contraindicated during pregnancy, but in case of severe gestosis in the later stages, when the benefit to the mother outweighs the risk of harm to the fetus, it is possible to use small doses of the drug in combination with other drugs.
"Vizin"
Tetrisoline-based vasoconstrictor drug used in ophthalmology. Under its influence, the pupil dilates, decreases conjunctival edema, and decreases intraocular fluid production. It is used in the treatment of allergic conjunctivitis, with the mechanical, physical or chemical effects of foreign agents on the mucous membrane of the eyelids.
Overdose of alpha-adrenergic agonists
Overdose is manifested by persistent changes characterizing the effects of alpha-adrenergic agonists. The patient is concerned about high blood pressure, an increased heart rate with rhythm disturbances. During this period, the development of a stroke or pulmonary edema is possible.
Overdose therapy consists in the use of the following groups of drugs:
- Peripheral sympatholytics disrupt the transmission of nerve impulses on the periphery and in the nervous system. Thus, pressure decreases, heart rate and peripheral resistance decrease.
- Calcium antagonists are aimed at blocking the flow of calcium ions into cells. The cardiac muscle reduces the need for oxygen, its contractility decreases, relaxation during the diastole period improves, and all groups of arteries expand.
- Myotropic drugs contribute to the relaxation of smooth muscles, including the muscle wall of blood vessels.
Alpha-adrenergic agonists, the use of which has a large group of indications, require careful selection of dosage, monitoring of electrocardiogram, blood pressure, peripheral blood.