Antiadrenergic

A sympatholytic (or sympathoplegic) drug is a medication that opposes the downstream effects of postganglionic nerve firing in effector organs innervated by the sympathetic nervous system (SNS). They are indicated for various functions; for example, they may be used as antihypertensives. They are also used to treat anxiety, such as Generalized Anxiety Disorder, Panic Disorder and PTSD.

Antiadrenergic agents inhibit the signals of epinephrine and norepinephrine. They are primarily postsynaptic adrenergic receptor antagonists (alpha and beta adrenergic receptor antagonists, or "blockers"), inhibiting the downstream cellular signaling pathways of adrenergic receptors. However, there are exceptions: clonidine is an adrenergic agonist at the α2 receptor; since this receptor is located presynaptically, agonism at this receptor inhibits the presynaptic release of adrenaline and noradrenaline, preventing postsynaptic adrenergic receptor activation and downstream signaling.

Another way to inhibit adrenergic receptor signaling is by blocking the synthesis of catecholamines. Methyltyrosine, for example, inhibits one of the key enzymes in the pathway: tyrosine hydroxylase.

For neurotransmitters to be released, they first must be stored in synaptic vesicles. Reserpine works by inhibiting VMAT, preventing the storage of neurotransmitters into synaptic vesicles. If VMAT is inhibited, neurotransmitters won't be released into the synaptic cleft, thereby inhibiting their downstream effect.

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