Rilmenidine activates postjunctional alpha 1- and alpha 2-adrenoceptors in the canine saphenous vein.
Experiments were performed to determine the subtypes of alpha-adrenoceptors involved in the contraction induced by rilmenidine in isolated canine cutaneous veins. Rings of saphenous vein (without endothelium) were suspended for the recording of isometric force in physiological salt solution. All experiments were performed in the presence of propranolol (to antagonize beta-adrenoceptors), cocaine (to inhibit neuronal uptake) and hydrocortisone (to inhibit extraneuronal uptake). In the presence of rauwolscine (an alpha 2-adrenergic blocker), rilmenidine caused concentration-dependent contractions which were inhibited by prazosin (nonselective alpha 1-antagonist) and by (+)niguldipine (selective alpha 1A-adrenergic antagonist), but not by (-)niguldipine. After treatment with phenoxybenzamine (to alkylate alpha 1-adrenoceptors), rilmenidine evoked contractions of the canine saphenous vein which were antagonized competitively by rauwolscine. The combination of rauwolscine and prazosin did not abolish contractions evoked by the highest concentrations of rilmenidine. Although binding experiments using 3H-idazoxan suggested the existence of a nonadrenergic binding site (around 20% of the total binding), contractile studies failed to demonstrate their involvement in the increases in tension evoked by rilmenidine. These experiments suggest that the contractions evoked by rilmenidine in isolated canine veins are mediated by both alpha 1A- and alpha 2-adrenoceptors.
Marsault
R
R
University of Padova, Department of Biomedical Sciences, Italy.
Taddei
S
S
Boulanger
C M
CM
Illiano
S
S
Vanhoutte
P M
PM
D058646:Adrenergic alpha-1 Receptor Agonists; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology; D004285:Dogs; D005260:Female; D019329:Idazoxan / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D054755:Imidazoline Receptors; D066298:In Vitro Techniques; D007553:Isotope Labeling; D008297:Male; D020926:Medetomidine; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D009994:Osmolar Concentration; D010080:Oxazoles / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D011869:Radioligand Assay; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D011955:Receptors, Drug / Q000187:drug effects; D000077769:Rilmenidine; D012501:Saphenous Vein / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium; D015016:Yohimbine / Q000494:pharmacology
D058646:Adrenergic alpha-1 Receptor Agonists; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D007093:Imidazoles; D054755:Imidazoline Receptors; D010080:Oxazoles; D011810:Quinoxalines; D018340:Receptors, Adrenergic, alpha-1; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; D010643:Phenoxybenzamine; D014316:Tritium; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D003000:Clonidine; D020926:Medetomidine; D000077769:Rilmenidine; D011224:Prazosin; D019329:Idazoxan; C054074:niguldipine