Sympatholytic

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Sympatholytic

 

a pharmacological substance that opposes the effects of the stimulation of sympathetic nerves, that is, the transmission of excitation from sympathetic nerves to effectors.

The action of sympatholytics corresponds to the physiological phenomena that arise with the relaxation of the tonus of the sympathetic nerves: the blood vessels dilate, systoles decelerate and arterial pressure decreases. Blockage of the transmission of excitation from sympathetic nerves to effectors is produced by the intervention of sympatholytics into the basic processes that occur in the presynaptic parts of adrenergic neurons. Sympatholytics are divided into groups according to the predominant effect they have on one of these processes, although as a rule several mechanisms can be distinguished in the action of every sympatholytic.

The first group of sympatholytics includes agents that cause the emptying of the depots of adrenergic mediators (norepinephrine and adrenaline) in the endings of sympathetic nerves. This group includes reserpine and oktadin, also called guaneth-idine, isobarin, or Ismelin. Initially, these sympatholytics may cause a short-term increase in arterial pressure resulting from the ejection of the mediators from the depots.

The second group of sympatholytics obstruct the release of mediators from depots located in the endings of sympathetic nerves. This group includes ornid, which is also called brety-lium tosylate. Many scientists also distinguish a group of sympatholytics that disrupt the biosynthesis of mediators (forming a false mediator) in the endings of sympathetic nerves. These agents include alpha-methyldopa, also called Aldomet.

In their influence on the functions of effectors innervated by sympathetic nerves, sympatholytics are similar to adrenolytic agents, including such adrenal blocking agents as phentola-mine, propionic acid, dihydroergotamine, and propanolol. These agents block adrenergic receptors and obstruct the action of mediators on them. Sympatholytics are used to lower arterial pressure in the treatment of hypertension.

REFERENCES

Zakusov, V. V. Farmakologiia, 2nd ed. Moscow, 1966.
Kaverina, N. V., and G. G. Chichkanov. “Simpatoliticheskie veshchestva.” In Itogi nauki: Seriia Biologiia, vol. 3. Moscow, 1972.
Anichkov, S. V. Izbiratel’noe deistvie mediatornykh sredstv. Leningrad, 1974.

V. V. ZAKUSOV