title: Heterogeneity of vascular alpha-adrenoceptors in man.
abstract: The knowledge on alpha-adrenoceptors has expanded enormously in the last decade, mostly as a result of in vitro and in vivo animal experiments. In the face of considerable species differences we have tested several of the newly developed concepts on alpha-adrenoceptors in the circulation of the human forearm. In this model we were able to show the presence of postsynaptic alpha 1- and alpha 2-adrenoceptors, both contributing to resting vascular tone. Although adrenaline and noradrenaline were shown to have affinity for each alpha-adrenoceptor subtype, noradrenaline seems to be the natural agonist for both receptors. Evidence is presented for an intrasynaptic location of the alpha 1-adrenoceptor and an extrasynaptic location of the alpha 2-adrenoceptor and also for a functional presynaptic alpha 2-adrenoceptor in the human forearm circulation. Selective hyperresponsiveness to alpha 1- or alpha 2-adrenoceptor stimulation in hypertensive patients could not be established. Calcium entry blockers were shown to attenuate the vasoconstriction induced by selective alpha 2-adrenoceptor stimulation but not by selective alpha 1-adrenoceptor stimulation. These data support the physiological and pharmacological relevance of the new concepts on alpha-adrenoceptors for the situation in man.
authors.affiliation: Department of Nephrology, University Hospital, Leiden, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: van Brummelen
authors.forename: K
authors.initials: K
authors.lastname: Jie
authors.forename: P B
authors.initials: PB
authors.lastname: Timmermans
authors.forename: P A
authors.initials: PA
authors.lastname: van Zwieten
mesh_terms: D001158:Arteries / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology; D005542:Forearm / Q000098:blood supply; D006801:Humans; D009638:Norepinephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction; D014680:Veins / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009638:Norepinephrine; D004837:Epinephrine