Elsevier

Life Sciences

Volume 21, Issue 5, 1 September 1977, Pages 595-606
Life Sciences

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A functional basis for classification of α-adrenergic receptors

https://doi.org/10.1016/0024-3205(77)90066-2Get rights and content

Abstract

The division of adrenergic receptors into alpha and beta types led to the development of selective and highly useful agents such as phentolamine, phenoxybenzamine, and propranolol. More recently, subdivision of beta receptors into β1 and β2 has resulted in the development of agents more selective for bronchodilation which are relatively free of cardiac stimulating properties. Response characteristics of alpha-adrenergic agonists are reviewed here which suggest the existence of at least two types of alpha-adrenergic receptors. Ag Agonists such as methoxamine and phenylephrine are relatively selective for postsynaptic alpha receptors mediating vasoconstriction. Agonists such as methylnorepinephrine, clonidine, and tramazoline are relatively selective for alpha-receptors mediating inhibition of neurotransmitter release from sympathetic neuron terminals. Members of this latter group are also relatively selective for alpha-receptors inhibitory to renin release from the kidney, alpha-receptors in the brain which lower blood pressure, alpha-receptors inhibitory to melanocyte stimulating hormone (MSH)-induced dispersion of melanocyte granules, and alpha-receptors in other systems. We propose a classification in which receptors of the vascular smooth muscle type are called α1 and those receptors of the type found on the sympathetic neuron terminal inhibitory to norepinephrine release, in the central nervous system inhibitory to the sympathetic nervous system, and on melanocytes inhibitory to dispersion of granules are called α2. Such a subclassification has been very useful in experimental design in our laboratories and in teaching. Also, this division could conceivably lead to the development of powerful agents even more selective for inhibition of renin release, control of blood pressure by a central site of action, reduction of fever, and possible other scientific or therapeutic applications.

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