Background: Patients treated with propranolol, a nonselective -adrenoceptor antagonist, have increased incidence and severity of anaphylaxis. We determined whether  1 -or  2 -adrenoceptor antagonist modulated pulmonary vasoconstriction and bronchoconstriction in rat anaphylactic hypotension. Methods: Anesthetized ovalbumin-sensitized male SpragueDawley rats were randomly allocated to the following pretreatment groups (n ϭ 7/group): (1) sensitized control (nonpretreatment), (2) propranolol, (3) the selective  2 -adrenoceptor antagonist ICI 118,551, (4) the selective  1 -adrenoceptor antagonist atenolol, and (5) adrenalectomy. Shock was induced by an intravenous injection of the antigen. Mean arterial pressure, pulmonary arterial pressure, left atrial pressure, central venous pressure, portal venous pressure, airway pressure, and aortic blood flow were continuously measured. Results: In either sensitized control or atenolol-pretreated rats, mean arterial pressure and aortic blood flow decreased substantially, whereas pulmonary arterial pressure and airway pressure did not increase soon after antigen injection. In contrast, in rats pretreated with either propranolol, ICI 118,551, or adrenalectomy, airway pressure significantly increased by 14 cm H 2 O, and pulmonary arterial pressure by