Blockade of β2-adrenoceptor, rather than β1-adrenoceptor, deteriorates cardiac anaphylaxis in isolated blood-perfused rat hearts.

Background: Cardiac anaphylaxis is one of the features of anaphylactic hypotension. Patients treated with propranolol, a nonselective β-adrenoceptor (AR) antagonist, develop severe anaphylaxis, but the mechanism remains unknown. Under examination were the effects of β1- and β2-AR antagonist on anaphylaxis-induced coronary vasoconstriction and cardiac dysfunction in isolated blood-perfused rat hearts.
Methods: Isolated hearts from ovalbumin-sensitized Wistar rats were subjected to coronary perfusion with blood at a constant pressure and measurements were made of coronary blood flow and left ventricu-lar (LV) pressure. Following pretreatment with selective β2-AR antagonist ICI118,551 or selective β1-AR antagonist atenolol, cardiac anaphylaxis was induced by intracoronary injections of ovalbumin antigen. LV contractility was evaluated by the maximum increasing rate of systolic LV pressure (dP/dtmax).
Results: In response to antigen administrations, ICI118,551 pretreated hearts showed a greater de-crease in coronary blood flow and consequently a greater increase in coronary vascular resistance than the atenolol pretreated hearts. Pretreatment with ICI118,551 caused a greater decrease in dP/dtmax than those with atenolol.
Conclusions: Cardiac anaphylaxis-induced contractile dysfunction and coronary spasm are severe in b2-, rather than β1-AR antagonist, pretreated isolated blood-perfused rat hearts.