Effects of propranolol on baroreflex sensitivity in borderline hypertension

Patients with borderline hypertension have reduced baroreflex sensitivity, but the mechanism is not known. These patients reportedly have increased beta-adrenergic activity. Since beta-adrenergic activity has been reported to antagonise baroreflex sensitivity, this study was undertaken, first to determine if propranolol increases baroreflex sensitivity in borderline hypertension, and secondly to test the hypothesis that increased beta-adrenergic activity might contribute to reduced baroreflex sensitivity in these patients. The effect of beta-adrenergic blockade on baroreflex sensitivity was studied in 11 patients with borderline hypertension and was compared with that of six age-matched control subjects. Baroreflex sensitivity was significantly increased by propranolol, 0.2 mg.kg-1 intravenously, in patients with borderline hypertension. However, after propranolol baroreflex sensitivity was still lower in the patients with borderline hypertension than it was in control subjects (P less than 0.01). The results suggest, first that increased beta-adrenergic activity is not a major factor contributing to decreased baroreflex sensitivity in borderline hypertension and, second that increased baroreflex sensitivity produced by propranolol might contribute to the anti-hypertensive effect of this drug.