Propranolol fails to lower the increased blood pressure caused by cold air exposure

Cold air exposure stimulates a rise in mean arterial blood pressure (MAP) and plasma norepinephrine (NE). The specific contribution of the beta-adrenergic receptor to this pressor response is unknown. Therefore, we pretreated 12 normal men with placebo or a bradycardia-inducing amount of propranolol prior to exposing them to either 25 degrees C or 4 degrees C air. At 25 degrees C, propranolol pretreatment lowered heart rate (HR) and MAP. When we compared changes in MAP after their respective 30-min exposure at 25 degrees C and 4 degrees C, the cold elevated MAP by 18.4 +/- 1.5 mm Hg in subjects pretreated with propranolol compared with 13.0 +/- 2.5 mm Hg in subjects pretreated with placebo. Fingertip skin temperature (Tfing) measured at 4 degrees C, 9.5 +/- 0.8 degrees C in propranolol-pretreated subjects was lower than the 11.1 +/- 0.7 degrees C with that of placebo. Plasma NE increased equally during cold exposure with both placebo and propranolol pretreatment. We conclude that the beta receptor plays a minor role in generating the pressor response to cold air. Therefore, the effectiveness of acute administrations of propranolol for maintaining normotension in subjects exposed to cold environments may be attenuated.