Postjunctional alpha-adrenoceptors and the regulation of arteriolar tone in humans.
The highly selective alpha-adrenoceptor agonists methoxamine (alpha 1) and azepexole (alpha 2), the less selective alpha-adrenoceptor agonists clonidine (alpha 2 greater than alpha 1) and guanfacine (alpha 2 greater than alpha 1), and the highly selective antagonists doxazosin (alpha 1) and yohimbine (alpha 2) were used to study post-junctional alpha-adrenoceptor subtypes in human blood vessels. Studies were done in healthy volunteers. All drugs were given intraarterially, and changes in forearm blood flow were measured by plethysmography. All agonists produced a significant and dose-dependent vasoconstriction. The effect of azepexole was abolished by yohimbine but hardly influenced by doxazosin. The reverse was found for methoxamine. The clonidine and guanfacine-induced vasoconstriction was partly prevented by both antagonists. Single infusions of doxazosin and yohimbine gave significant vasodilation. It is concluded that post-junctional alpha 1-and alpha 2-adrenoceptors are present in human blood vessels and contribute to basal vascular tone. In a second study, it was shown that both alpha-adrenoceptor subtypes are involved in the vasoconstrictor effect of exogenous adrenaline and noradrenaline. No preference was found of either catecholamine for the postjunctional alpha 1-and alpha 2-adrenoceptor.
P
P
van Brummelen
K
K
Jie
P B
PB
Timmermans
P A
PA
van Zwieten
D001132:Arm / Q000098:blood supply; D001158:Arteries / Q000502:physiology*; D001160:Arterioles / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D009638:Norepinephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D017981:Receptors, Neurotransmitter / Q000502:physiology; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction; D014666:Vasomotor System / Q000502:physiology
D011942:Receptors, Adrenergic, alpha; D017981:Receptors, Neurotransmitter; D009638:Norepinephrine; D004837:Epinephrine