Propranolol effects on autonomic function in hypertensive men

Beta blocker antihypertensive effects are incompletely understood, and may involve alterations in the autonomic nervous system. We studied autonomic function in 12 essential hypertensive men during treatment with placebo and chronic oral propranolol. Propranolol reduced blood pressure and heart rate (both p less than 0.01) with an associated increase in baroreflex sensitivity during phenylephrine testing (p less than 0.02), though amyl nitrite-tested baroreflex sensitivity was unchanged; blood pressure decrement did not correlate with baroreflex enhancement. Response to the cold pressor test and the blood pressure decrement to phentolamine alpha blockade were unaltered by propranolol, suggesting unchanged efferent sympathetic function; nor were several biochemical indices of sympathetic nervous activity influenced by propranolol. Propranolol does perturb autonomic function in man, but the perturbations do not correlate with blood pressure decrement; nor are physiologic or biochemical indices of efferent sympathetic activity reduced by propranolol.