Effects of clenbuterol as a repartitioning agent on beta-adrenoceptor concentrations in heart, bronchi and brain of veal calves.
The effects induced by dietary clenbuterol (20 micrograms kg-1 body weight day-1 for 40 days) on beta-adrenergic receptor (beta-AR) subtypes in the heart, bronchial smooth muscles and the CNS of veal calves were investigated using a binding method. Clenbuterol exposure caused a significant (P < 0.05, P < 0.01, P < 0.001) decrease in beta 1-AR and beta 2-AR in both cardiac atria and ventricles of treated animals (excluding the beta 2-AR of the right atrium). Similarly, a significant (P < 0.01, P < 0.001) down-regulation of beta-AR subtypes in bronchial smooth muscles of treated calves was observed. In the CNS (cerebral cortex, hippocampus, hypothalamus and cerebellum) the down-regulation was limited to beta 2-AR, with the exception of the hippocampus in which both beta 1-AR and beta 2-AR concentrations were significantly (P < 0.05; P < 0.01) reduced. Scatchard analysis of the binding of the beta-AR antagonist, (-) [3H]CGP 12177, revealed that the down-regulation of beta-AR was not associated with any modification in binding affinity, as Kd values were unaffected by clenbuterol treatment. Data obtained indicated that prolonged clenbuterol exposure induced a remarkable beta-AR down-regulation in the heart, bronchi and brain of veal calves.
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Department of Animal Pathology, University of Turin, Italy.
Badino
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Novelli
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Girardi
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D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D002976:Clenbuterol / Q000494:pharmacology*; D015536:Down-Regulation / Q000502:physiology; D006321:Heart / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000032:analysis / Q000187:drug effects* / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D002976:Clenbuterol