EFFECTS OF CLENBUTEROL TREATMENT ON THE RESPONSES TO VASODILATORS IN URETHANE-ANESTHETIZED RATS

Abstract— Seven or 14 days of treatment with the β2‐adrenoceptor agonist clenbuterol, 0.3 mg kg−1, s.c., twice daily, increased the basal mean blood pressure in normotensive urethane‐anaesthetized rats. The elevated pressure values were maintained until 48 h after the end of the 14 day treatment. Clenbuterol treatment decreased the vasodilatory responses to the β‐adrenoceptor agonist isoprenaline and adenosine, agents which act through an increase in intracellular cyclic AMP. Decreased responses were maintained until 48 h after a 14 day treatment with clenbuterol. On the other hand, its administration to rats for 14 days did not modify the vasodilator responses to acetylcholine or sodium nitroprusside, two agents that exert their effects by enhancing cyclic GMP. The increase in mean blood pressure in urethane‐anaesthetized rats after clenbuterol treatment may be a consequence of a reduced vasodilator β2‐adrenoceptor‐mediated response to circulating catecholamines. 1990 Royal Pharmaceutical Society of Great Britain