Antisympathotonic

Antisympathotonics are substances that reduce the activity and affinity of the sympathetic part of the autonomic nervous system. They reduce the concentration of noradrenalin in the peripheral noradrenergic synapses of the sympathetic nervous system (sympathotonic). The sympathotonus can thus be defined as "the total concentration of noradrenalin in the synapses of the (postganglionic) neurons of the sympathetic nervous system".

The sympatholytic, i.e. the sympathotonus-lowering effect of the preparations can be explained on the one hand by:

• an emptying of the noradrenanlin stores in the noradrenergic neurons(Reserpin, an indole alkaloid from the plant group of the snakeroot)
• or on the other hand via
• a reduction in the action potential in the pre- and postganglionic neurons of the sympathetic nervous system and a decrease in the release of noradrenaline from the noradrenergic neurons (alpha2-receptor agonists).0

This group of drugs includes:

• Clonidine
• Moxonidine
• alpha-methyldopa

For alpha-methyldopa an activation of the central alpha2-adrenoreceptors is assumed. These have an inhibitory effect on the release of noradrenaline. Alpha-methyldopa can pass the blood-brain barrier and inhibits enzymes responsible for the formation and release of noradrenalin. Alpha-methyldopa is a pharmaceutical precursor. It is metabolised in the periphery and in the CNS like dopa. This produces a false transmitter (alpha-methylnoradrenaline), which, in contrast to noradrenaline, acts as an alpha-2-selective agonist. Furthermore, alpha-methyldopa also acts as an inhibitor of dopa decarboxylase. It thus also suppresses the synthesis of dopamine, noradrenaline and adrenaline.

Arterial hypertension: Antisympathotonic drugs are hardly used therapeutically nowadays because of their side effects.

However, alpha-methyldopa is the first choice for the treatment of hypertension during pregnancy.

The main indication for clonidine is alcohol and opioid withdrawal. Furthermore it reduces the intraocular pressure when applied topically

1. Cifková R (2000) Hypertension in pregnancy: recommendations for diagnosis and treatment. J. Hypertens 18: 1346-1348
2. Podymow T et al (2008) Update on the Use of Antihypertensive Drugs in Pregnancy. Hypertension 51: 960-969