In case I forgot, better post something that worth to memorize
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Adrenergic Receptors
Adrenergic responses are those activated by "adrenaline"-like compounds. Within the body, Epinephrine
(the generic name for adrenaline), and Norepinephrine are the primary adrenergic transmitters. Isoproterenol is an example of an extrinsic drug which stimulates some adrenergic responses. When the target responses of adrenergic stimulation are examined in various body systems, they fit into several categories of response, as summarized in the following table:
These diverse responses to adrenergic stimulation results from the activity of two different classes of adrenergic receptor, named Alpha and Beta by Ahlquist in 1948 on the basis of their pharmacology. Each of these classes is further subdivided into subclasses. Their properties are outlined below.
Alpha Receptors
- Epinephrine (E) and norepinephrine stimulate about equally well, and both are much more effective than isoproterenol (I). E >= NE >> I.
- Selectively stimulated by Phenylephrine.
- Selectively blocked by Phentolamine and Phenoxybenzamine.
- Two subclasses of alpha receptor have since been identified:
Alpha1
- Predominant form of alpha receptor in the body.
- Found primarily in the smooth muscles of arterioles, eye, gut, skin, veins, etc., as well as in some other cell types (like salivary glands).
- Usually causes contraction of smooth muscle cells.
Alpha2
- Found at pre-synaptic terminals of adrenergic nerves.
- Functions as an autoreceptor. If stimulated, it decreases the subsequent release of transmitter.
Beta Receptors
- Isoproterenol stimulates best, epinephrine is also effective, and norepinephrine is often weaker. I > E >= NE.
- Blocked by propranalol.
- Several subclasses of beta receptor have been identified on the basis of their detailed pharmacology:
Beta1
- Found in heart muscle, and in the kidney.
- Causes increased heart rate and contractility.
- Promotes release of renin from the kidney.
- EPI and NE are about equally effective in their ability to stimulate beta1 receptors.
Beta2
Found in smooth muscle that relaxes upon stimulation, and in metabolic tissues.
Causes:
- Decrease in gastrointestinal motility.
- Bronchodilation.
- Vasodilation in skeletal and cardiac muscle.
- Glycogenolysis in the liver.
EPI is much more effective than NE. EPI can also stimulate beta2 receptors at lower concentrations than required to stimulate alpha receptors.
Beta-3
- Found in adipose tissue (fat cells).
- Stimulates lipolysis, increasing fatty acids in the blood.
- EPI and NE are about equally effective in their ability to stimulate beta3 receptor
Alpha 1 adrenergic drugs1. Agonist
- Noradenaline
- Phenylephrine
- Methoxamine
- Cirazoline
- Xylometazoline
2. Antagonist (Alpha 1 blockers)
- Alfuzoxine
- Doxazosin
- Phenoxybenzamine
- Prazosin
- Tamsulosine
- Terazosin
Alpha 2 adrenergic drugs1. Agonist
- Medetomidine
- Romifidine
- Clonidine
- Detomidine
- Xylazine
- Tizanidine
2. Antagonist
- Phentolamine
- Yohimbine
- Idazoxan
- Atipamizole
Beta 1-adrenergic drugs1. Agonist
- Noradrenaline
- Isoproline
- Dobutamine
2. Antagonist
- Metoprolol
- Atenolol
Beta 2 adrenergic drugs1. Agonist
- Bitolterol mesylate
- Levalbuterol
- Metaproterenol
- Terbutaline
- Ritodine
- Salbutamol
2. Antagonist
- Propanolol
- Butoxamine
Ps: I really need to refresh all this!
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