Sympathetic nervous system response to graded exercise: effect of beta-blockade.
This study compares the sympathetic nervous system response to graded exercise in normotensive and essential hypertensive subjects with and without beta-adrenergic blockade. Blood pressure (BP), heart rate, and plasma norepinephrine (NE), epinephrine (E), and dopamine (DA) were measured just before starting the exercise (Pre-Ex), in the submaximal exercise (Sub-max),and after 8 minutes rest (Post-Ex). On placebo, Sub-max induced in both normotensives and hypertensives a similar increase in NE and E plasma levels. Plasma DA remained unchanged. Propranolol in controls and propranolol or mepindolol in hypertensives didn't modify significantly: 1) Pre-Ex plasma levels of E, NE, and DA; 2) response at Sub-max in controls; 3) plasma E and DA in hypertensive patients. In hypertensives on beta-blockade, submaximal exercise elicited a greater increase in plasma NE. Values for plasma NE in patients on propranolol were 1135 +/- 229 pg/ml higher than those obtained in the same patients on placebo (p less than 0.001). On mepindolol, the plasma NE increment was higher than that on placebo (p less than 0.05), but lower than that on propranolol (p less than 0.01). In controls, propranolol did not significantly modify BP at Pre-Ex or its response to exercise, whereas systolic and diastolic BP were significantly lower at Pre-Ex, Sub-max, and Post-Ex in hypertensives. On beta-blockade, heart rate decrease in Pre-Ex, Sub-max, and Post-Ex were not different in controls and hypertensives. The differences found on beta blockade would indicate that the effects of beta blockers are not identical in normotensive and hypertensive subjects.