Sympatholytic

A sympatholytic is a medication which inhibits the functioning of the sympathetic nervous system (SNS). They are used as antihypertensives.

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They mainly comprise antiadrenergic agents, but also anticholinergics in the case of the nicotinic antagonist, since nicotinic receptors relay the signals of the SNS across the ganglia.

Antiadrenergic

Antiadrenergic agents inhibit the signals of adrenaline and noradrenaline. They are mainly adrenergic antagonists, inhibiting adrenergic receptors, but there are exceptions: clonidine is an adrenergic agonist on the α2 receptor, since this receptor is located presynaptically to inhibit further release of adrenaline and noradrenaline.

Other ways of inhibiting adrenergic signaling is by catecholamine synthesis blocking, e.g. by methyltyrosine. Reserpine works by inhibiting transport into synaptic vesicles of noradrenaline by inhibiting the VMAT transporter.

In hypotension

Many antiadrenergic agents used as antihypertensives include:

• centrally acting:
  • Clonidine (α2 agonist)
  • Guanfacine (α2 agonist)
  • Methyldopa (α2 agonist)
  • Moxonidine (imidazoline receptor agonist)
  • Rescinnamine (ACE inhibitor)
  • Reserpine (VMAT inhibitor)
  • Rilmenidine (imidazoline receptor agonist)
• ganglion-blocking
  • Mecamylamine (α3β4 nicotinic receptor inhibitor)
  • Trimethaphan (ganglion type receptor inhibitor)
• peripherally acting
  • Prazosin (α1 antagonist)
  • Guanethidine (Magnesium-ATPase inhibitor)
  • Indoramin (α1 antagonist)
  • Doxazosin (alpha blocker)