The rat lipolytic beta-adrenoceptor: studies using novel beta-adrenoceptor agonists.

EC50 and relative intrinsic activity values were obtained for isoprenaline, fenoterol, salbutamol, prenalterol and three new beta-adrenoceptor agonists, BRL 28410, BRL 35113 and BRL 35135 on rat white adipocyte lipolysis, rat atrial rate and tension, rat uterus tension and guinea-pig tracheal tension. Fenoterol and salbutamol were selective for tracheal and uterine responses, prenalterol was selective for atrial responses, but BRL 28410, BRL 35113 and BRL 35135 were selective for the adipocyte lipolytic response. pA2 values for propranolol, practolol, ICI 118,551 and sotalol were obtained on adipocytes, atria and trachea. pA2 values for propranolol and sotalol were much lower on adipocytes than on atria or trachea. The pA2 value for practolol was lower on adipocytes than on atria and the pA2 value for ICI 118,551 was lower on adipocytes than on trachea. Both agonist and antagonist studies therefore suggest that the rat adipocyte lipolytic receptor does not fit into the current beta 1/beta 2-adrenoceptor classification.