title: Different contractile effects of alpha1- and alpha2-adrenergic agonists on horse isolated common digital artery smooth muscle ring preparations in vitro.
abstract: Despite assays on ring preparations in vitro confirmed that the vasoconstrictor sympathetic control in the horse common digital artery mainly depends on alpha(1)-adrenoceptors stimulation, selective alpha(2)-adrenoceptor agonists were investigated under the same experimental conditions. Both detomidine (DET) and UK 14304 differed from noradrenaline (NA) and phenylephrine (PHE) in provoking contractile effects which were slowly onsetting, concentrations-unrelated and unremovable by repeated washings. While prazosin (PRA) clearly antagonized the effects of NA and PHE, neither pre- nor post-treatments of the preparations with alpha(2)-antagonists succeeded in antagonizing or removing the effects of the two alpha(2)-agonists tested, which moreover were unaffectable either by lowering the organ bath temperature or by depriving the nutritive medium of Ca(2+). To explain this unusual behavior of alpha(2)-adrenoceptors stimulation it has been hypothesized that a Ca(2+) mobilization from the endoplasmic reticulum of the smooth muscle cell occurs which is followed by a hindered reuptake of them.
mesh_terms: D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D065128:Endothelin Receptor Antagonists; D004730:Endothelium, Vascular / Q000502:physiology; D006736:Horses / Q000502:physiology*; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology
chemical_list: D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D065128:Endothelin Receptor Antagonists; D007093:Imidazoles; D009842:Oligopeptides; D010456:Peptides, Cyclic; D010880:Piperidines; D011810:Quinoxalines; D010656:Phenylephrine; C086539:BQ 788; D000068438:Brimonidine Tartrate; C041255:detomidine; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium; D009638:Norepinephrine