Comparative effects of beta-, alpha- and combined beta- plus alpha-adrenoceptor blocking agents in stress-induced increase in arterial blood pressure.

Comparative efficacy of cardioselective beta-adrenoceptor blocker (atenolol), non cardioselective beta-adrenoceptor blocker (propranolol), alpha-adrenoceptor blocker (prazosin) and combined alpha plus beta-adrenoceptor blocking agent (labetalol) on cold stress and hand grip exercise-induced increase in arterial blood pressure and heart rate was studied in 7 healthy volunteers. The design of the trial was controlled, randomized, double blind and crossover. All the 4 drugs produced a fall in both supine and sitting systolic as well as diastolic blood pressure. Basal heart rate was reduced by propranolol and atenolol whereas prazosin and labetalol did not produce any change. The increase in both systolic and diastolic blood pressure induced by cold stress was significantly (p less than 0.01) reduced by labetalol, prazosin and atenolol in the decreasing order of efficacy. The increase in systolic blood pressure due to hand grip exercise was reduced significantly (p less than 0.05) by all the 4 drugs and the most effective drug was labetalol. However, the increase in diastolic blood pressure due to hand grip exercise was not reduced significantly by any of the drugs. Therefore, combined alpha and beta-receptor antagonist is more effective in reducing the spikes of blood pressure rise due to these stressful conditions as compared to pure alpha or beta-adrenoceptor antagonists.