title: An increase in cardiac alpha 1-adrenoceptors following chronic clonidine treatment.
abstract: Chronic treatment (22 days) of rats with clonidine (0.5 mg/kg s.c. twice a day followed by 20 h of withdrawal) resulted in a significant increase in the specific [3H]WB4101 binding to ventricular and intraventricular septal alpha 1-adrenoceptors but no alteration of the atrial alpha 1-adrenoceptors. Scatchard analysis indicated that the increase in the [3H]WB4101 binding to the clonidine-treated cardiac tissue was due to an enhancement of the alpha 1-adrenoceptor density since there was a significant increase in the Bmax value for the [3H]WB4101 binding to the treated ventricles without a change in the Kd value. The specific [3H]WB4101 binding to cardiac alpha 1-adrenoceptors was not altered by the acute (1 day) or 7 days treatment with clonidine. Chronic treatment with clonidine had no significant effect on the specific [3H](-)DHA binding to the atrial and ventricular beta-adrenoceptor. The noradrenaline (NA) concentrations in the clonidine-treated ventricles and intraventricular septae were decreased by 16-20%. These data provide biochemical evidence compatible with a significant reduction of sympathetic outflow to the ventricular myocardium by clonidine.
mesh_terms: D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D004082:Dihydroalprenolol / Q000378:metabolism; D004146:Dioxanes / Q000378:metabolism; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects
chemical_list: D004146:Dioxanes; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D003000:Clonidine; D009638:Norepinephrine