Adrenergic antagonists in animals
Adrenergic antagonists or Antiadrenergic drugs in animals are drugs that interfere with the functions of the sympathetic nervous system either by blocking the adrenergic receptors or by interfering the synthesis, storage or release of nor adrenaline in sympathetic nerve terminals.
- Accordingly these drugs are divided into two groups-
- Adrenergic receptor antagonists
- Adrenergic neuron blocking drugs
Differences between adrenergic receptor antagonists and adrenergic neuron blocking drugs
| Adrenergic receptor antagonists | Adrenergic neuron blocking drugs |
| Act on post junctional or pre junctional Receptors | Act on adrenergic neuron membrane (pre junctional) |
| Act by blocking adrenoceptors (alpha and beta) | Act by inhibiting synthesis, storage or release of nor adrenaline |
| Effects of exogenous adrenergic drugs is blocked | Not blocked |
1. Adrenergic receptor antagonists
Adrenergic receptor antagonist drugs interact with adrenergic receptors (α and / or β) on effector cells (post junctional) or on adrenergic neurons ( pre junctional) and prevent their access to either endogenous catecholamines or exogenous adrenergic drugs, except phenoxybenzamine, almost all these drugs act as competitive antagonists.
- These are further divided into three groups, based on the type of receptors they antagonize-
2. Adrenergic neuron blocking drugs
Adrenergic neuron blocking drugs act on pre junctional adrenergic neurons to interfere with or adrenaline synthesis, storage or release.
- Some drugs also affect the reuptake of the released nor adrenaline from synaptic cleft. Accordingly these are divided into-
- Drugs that affect noradrenaline synthesis– α-methyl-p-tyrosine, Carbidopa, α- methyldopa
- Drugs that affect noradrenaline storage– Reserpine.
- Drugs that affect noradrenaline release– Guanethedine, Guanadral, Reserpine, Bretylium
- Drugs that inhibit noradrenaline reuptake– Tricyclic antidepressants like imipramine, amitriptyline, cocaine