Λεξικό .. (alpha)-adrenoceptors

(alpha)-adrenoceptors

The adrenergic inhibitory system function by activating one or a combination of the following five receptors: Receptors stimulated by noradrenaline, adrenaline and sympathomimetic substances (See Adrenoceptors, Receptors).

The α1- receptors; the α2-receptors; the β1-receptors; the β2-receptors; the β3- receptors. Recent evidence indicates that there is additional heterogeneity of both α1- and α2- adrenergic receptors (α1Α, α1Β, α2Α, α2Β, etc.

α-receptors mediate the contraction of airway smooth muscle. They have been demonstrated in many species, including man, although it may only be possible to demonstrate their presence under certain conditions. Autoradiographic studies have confirmed a very low density of α1-receptors in smooth muscle of large airways, but have released a surprisingly high density in small airways [1]. α-Αgonists stimulate mucus secretion and α1-receptors have been demonstrated autoradiographically on serous cells of submucosal glands. Two subtypes of α-receptor have now been recognized with the development of selective α-agonists. α1 receptors are mediating the conractile effect and are selectively blocked by prazosin. The presynaptic α-receptors mediating negative feedback of norepinephrine release and selectively blocked by yohimbine and are termed α2-receptors. α2 receptors have also been found postsynaptically [2].

References

Barnes P.J., Basbaum C.B.: Mapping of adrenergic receptors in mammalian trachea using an autoradiographic method, Exp. Lung Res. 1983;5:183-92.

Barnes, P.J. et al: Autoradiographic localization of autonomic receptors in airway smooth muscle: marked differences between large and small airways. Am. Rev. Respir. Dis 1983;127:758-62.