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Nathan
New member
I was doing some reading on beta-receptors and I thought I might share some info (everyone's always mentioning 'em):
All cell surfaces bear receptors of many types and receptors for catecholamines form one group. They are part of a larger family of receptors which bind small molecules, peptide hormones or
neuro-transmitters, coupling through guanine-nucleotide-binding regulatory proteins (G proteins) to modulate the cellular level of a second-messenger molecule. The adrenergic receptors are part of the sympathetic nervous system and are characterised by their interaction with the endogenous catecholamines adrenaline
and, the neurotransmitters, noradrenaline. There are two major sub-groups, the alpha-receptors and the beta-receptors. Stimulation of the alpha-receptor is associated with intestinal relaxation,
vasoconstriction and the stimulation of the uterus, nictitating membrane, ureter and pupil dilation. Stimulation of the beta-receptor is associated with myocardial stimulation, vasodilation and inhibition of the
uterine and bronchial musculature. The two groups are distinguished by their differing responsiveness to a series of ligands closely related to adrenaline.
Beta-Adrenergic receptors are associated with all tissues involved in growth including skeletal muscle and adipose tissue. It was shown initially that receptors could be differentiated into two subtypes, beta1
and beta2. This was accomplished by monitoring the receptor's affinity for a range of ligands. The beta1 receptor was associated with cardiac stimulation and the beta2 receptor with
bronchial smooth muscle relaxation. However, recently it has been shown that the beta-receptor on brown adipose tissue was not a mixed population of the two types but unique,
the beta3. This receptor is associated with lipolysis. The beta3 stimulates lipolysis within adipose tissue and increases blood flow and thermogenesis in the brown adipose tissue, all
of which are implicated in fat decretion.
Skeletal muscles, mainly type II muscle fibres, are thought to carry beta1-receptors while smooth muscle contains beta2-receptors. Most of the side effects of beta-agonist growth promoters are caused by cross stimulation of the beta-receptor subtypes. Generally, ligands specific for
either alpha-or beta-adrenergic receptors have only about one hundred fold affinity between types, and only about ten fold within subtypes. For instance clenbuterol has only a six fold affinity for the beta2
subtype over the beta1.
All cell surfaces bear receptors of many types and receptors for catecholamines form one group. They are part of a larger family of receptors which bind small molecules, peptide hormones or
neuro-transmitters, coupling through guanine-nucleotide-binding regulatory proteins (G proteins) to modulate the cellular level of a second-messenger molecule. The adrenergic receptors are part of the sympathetic nervous system and are characterised by their interaction with the endogenous catecholamines adrenaline
and, the neurotransmitters, noradrenaline. There are two major sub-groups, the alpha-receptors and the beta-receptors. Stimulation of the alpha-receptor is associated with intestinal relaxation,
vasoconstriction and the stimulation of the uterus, nictitating membrane, ureter and pupil dilation. Stimulation of the beta-receptor is associated with myocardial stimulation, vasodilation and inhibition of the
uterine and bronchial musculature. The two groups are distinguished by their differing responsiveness to a series of ligands closely related to adrenaline.
Beta-Adrenergic receptors are associated with all tissues involved in growth including skeletal muscle and adipose tissue. It was shown initially that receptors could be differentiated into two subtypes, beta1
and beta2. This was accomplished by monitoring the receptor's affinity for a range of ligands. The beta1 receptor was associated with cardiac stimulation and the beta2 receptor with
bronchial smooth muscle relaxation. However, recently it has been shown that the beta-receptor on brown adipose tissue was not a mixed population of the two types but unique,
the beta3. This receptor is associated with lipolysis. The beta3 stimulates lipolysis within adipose tissue and increases blood flow and thermogenesis in the brown adipose tissue, all
of which are implicated in fat decretion.
Skeletal muscles, mainly type II muscle fibres, are thought to carry beta1-receptors while smooth muscle contains beta2-receptors. Most of the side effects of beta-agonist growth promoters are caused by cross stimulation of the beta-receptor subtypes. Generally, ligands specific for
either alpha-or beta-adrenergic receptors have only about one hundred fold affinity between types, and only about ten fold within subtypes. For instance clenbuterol has only a six fold affinity for the beta2
subtype over the beta1.
