Selective and nonselective beta-adrenoceptor blockade in hypertension: responses to changes in posture, cold and exercise.

Abstract

The hypertensive response to the infusion of epinephrine is exaggerated in subjects treated with noncardioselective .beta.-adrenergic antagonists, but not in subjects given cardioselective agents. Whether the same holds true when hypertensive patients treated with these drugs are subjected to acute physiologic stress was determined. According to a randomized crossover protocol, 13 hypertensive men received oral metoprolol and propranolol for 5 wk each. The dosage was adjusted to maintain diastolic resting blood pressure at 80-90 mm Hg. During the last week of each treatment period, measurements were made of responses to a change in posture (lying to erect), isometric hand grip, hand immersion in cold water and progressive incremental and steady-state exercise on a cycle ergometer. In addition to within-patient comparison of the 2 drugs, the responses were also compared with those in 6 healthy untreated controls. The increases in blood pressure associated with the pressor tests were similar during treatment with the 2 drugs. The heart rate increased less in controls and was similar in the 2 treatments. During incremental exercise, ventilation was significantly lower during propranolol treatment than during metoprolol. This effect was not found during steady-state exercise, probably owing to a reduced rate of adaptation to exercise with propranolol. During steady-state exercise, cardiac output was similar with the 2 treatments. The extent of pressor responses to cold stimulus and to isometric and dynamic exercise was similar during selective and nonselective .beta.-blockade, so such increases in blood pressure are largely mediated by neural sympathetic pathways rather than by circulating epinephrine. In hypertensive patients, selective .beta.-antagonists confer no benefits over nonselective antagonists in the presence of blood pressure surges associated with hand immersion in cold water and isometric and dynamic activity.