Effect of Adrenergic Receptor Blockade on the Responses to Isometric Handgrip

Heart rate and blood pressure (BP) responses to a standardized 3 min isometric handgrip (IHG) test were measured in 32 normotensive men and compared with those found in 35 age-matched, drug-free men with established essential hypertension (BP range: 140--170/90--110). IHG testing in the normal subjects induced significant increases in heart rate (mean +/- SE: 7.6 +/- 3.3 beats/min), systolic blood pressure (19.4 +/- 5.3 mm Hg), and diastolic blood pressure (15.6 +/- 4.6 mm Hg). Although beginning from higher resting levels the hypertensive patients had similar degrees of increase in all three parameters. After chronic treatment with propranolol, the heart rate increase with IHG was suppressed in both study groups, but blood pressure responses differed, with a diminished pressor response to IHG seen in normal subjects and augmented pressor effects in the hypertensive group. Intravenous administration of phentolamine and propranolol completely abolished the pressor effects of IHG. These observations suggest that the autonomic control mechanisms mediating the responses to isometric exercise function similarly in drug-free normal and hypertensive patients and that the responses to IHG, mediated largely by endogenous catecholamine release, can be prevented by peripheral sympathetic receptor blockade.