Vasodilators of central action

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Description of the pharmacological group

Vasodilators of the predominantly central action

The medicines, which realize their vaso-dilating action at the level of central nervous system, include the preparations of clonidine, methyldopa, guanfacine and moclobemide.

Clonidine realizes its action in essence at the level of the alpha₂- presynaptic adrenergic receptors, localized on the presynaptic membranes of the noradrenergic synapses of the medulla oblongata. Alpha₂- presynaptic adrenoreceptors relate to the group of brake autoreceptor, i.e., their excitation it is accompanied by the curtailment of the isolation of neuromediator, in this case - noradrenaline, into the synaptic slot.

As a result is suppressed the activity of vasomotor center, situated on the bottom IV of the ventricle of the brain in the region of the reticular formation of the medulla oblongata; vasomotor center coordinates the activity of the neurons of the sympathetic division of peripheral nervous system, localized in the breast and lumbar divisions of spinal cord and which send on the periphery vasomotor pulses) and, therefore, decreases sympathetic tone. At the level of organism this effect realizes in a decrease in arterial pressure, the retarding heart rate and decreasing the level of catecholamines (noradrenaline, adrenaline) in the circulating blood. Simultaneously reduction in the impact volume of heart occurs with this. The decrease of the tone of the sympathetic division of peripheral nervous system entails an increase in the tonic activity of its parasympathetic division, which also introduces its contribution to reduction in the total resistance of vessels, decrease of frequency and force of the heart contractions.

In the clinical practice of clonidine they use for treating of arterial hypertonia and stopping of hypertonic crises. Preparation is usually transferred well by patients, but one should remember that against the background its application is possible the development of orthostatic hypotension (sin.: postural hypotension - sharp decrease in arterial pressure, which appears as a result of the passage of body from horizontal to vertical position). Orthostatic hypotension against the background of the application of clonidine is caused by the fact that does not occur the activation of sympathetic tone, within the standard observed upon transfer from horizontal to vertical position.

Guanfacine (sin.: estulic) and methyldopa (sin.: aldometh), just as clonidine, cause a decrease AD as a result of the activation of a2- presynaptic adrenoreceptors, localized in the medulla oblongata. To methyldopa can be considered as prodrug, since after overcoming blood-brain barrier, it is metabolized in the cloths of CNS to alpha-methylnorepinephrine, which interacts with the presynaptic α2- adrenoreceptors.

Apparently, methyldopa and clonidine interact with different subtypes of the α2- adrenoreceptors, located in the vasomotor center of the medulla oblongata, since methyldopa to a lesser degree decreases the heart emission and the frequency of the heart contractions.

At the end of 1980's in the medulla oblongata were isolated imidazoline receptors, which, as was explained somewhat later, takes active part in the regulation of the tone of cardiovascular system.

Later were synthesized and inculcated in the wide clinical practice the agonists of central imidazoline receptors, which possess the expressed hypotensive activity. The medicines of this group include the preparations of moxonidine and rilmenidine. Against the background the application of these preparations, as a result of the suppression of the tonic activity of vasomotor center, stably is reduced level AD, is reduced the general peripheral resistance of vessels (total peripheral vascular resistance) and decreases heart rate. Besides this in the nephrons of kidneys decreases the reabsorption of water and ions of Na⁺, the liberation of catecholamines from the chromaffin cells of the medullary layer of the adrenal glands is impeded.

Means of central are used to treat diseases of the vessels of the brain and peripheral vessels