ALBUTEROL HAS A PREFERENTIAL EFFECT ON BETA-2 ADRENERGIC RECEPTOR COMPARED WITH ISOPROTERENOL. THE PHARMACOLOGIC EFFECTS OF BETA-ADRENERGIC AGONIST DRUGS, INCLUDING ALBUTEROL,ARE AT LEAST IN PART ATTRIBUTABLE TO STIMULATION THROUGH BETA- ADRENERGICRECEPTORS OF INTRACELLULAR ADENYL CYCLASE, THE ENZYME THAT CATALYZES THE CONVERSION OF ADENOSINE TRIPHOSPHATE (ATP) TO CYCLIC- 3',5'-ADENOSINE MONOPHOSPHATE (CYCLIC AMP). INCREASED CYCLIC AMP LEVELS ARE ASSOCIATED WITH RELAXATION OF BRONCHIAL SMOOTH MUSCLE AND INHIBITION OF RELEASE OF MEDIATORS OF IMMEDIATE HYPERSENSITIVITY FROM CELLS, ESPECIALLY FROM MAST CELLS.