Comparative effect of propranolol and labetalol on isometric exercise and cold stress induced increase in arterial blood pressure.

The effect of propranolol and labetalol on cold stress and isometric exercise induced rise of blood pressure was studied in 7 patients with essential hypertension and 14 normal volunteers in a controlled, double blind, randomized, cross-over trial design. The subjects received either propranolol (40 mg) or labetalol (100 mg) orally after breakfast. In patients of mild to moderate essential hypertension, labetalol reduced significantly both systolic as well as diastolic rise of blood pressure induced by both types of exercises. Propranolol only reduced the rise of systolic blood pressure significantly. In normotensive subjects, labetalol reduced significantly the rise in systolic as well as diastolic blood pressure induced by cold stress, but not by the isometric exercise, while propranolol only reduced significantly the rise in systolic blood pressure induced by both the tests. The rise in heart rate was more with isometric exercise than with cold stress both in hypertensive patients and control subjects. The heart rate rise was significantly reduced by propranolol in all the experiments except for the rise induced by cold stress in hypertensive patients. The changes in heart rate produced by labetalol were not significant.