Biochemical and dynamic responses to single and repeated doses of methyldopa and propranolol during dynamic physical...

Our purpose was to describe changes in potassium disposition with antirenin antihypertensives during dynamic physical activity in normal subjects receiving methyldopa and propranolol. Before the study, 2 hr after dosing and coincident with immediate preexercise on treadmill (at graded increases of exercise), and 2 hr after exercise, blood was sampled for determination of potassium, renin, aldosterone, and catecholamine levels. Blood pressure and heart rate were measured. The results demonstrate no greater increase in potassium after single or multiple doses of methyldopa than after placebo. After the first dose of propranolol there was a greater rise in potassium over that with placebo, but it was not observed after multiple doses, which may be related to the low doses. There were minor, but significant, changes in norepinephrine, renin, and systolic pressure with multiple-dose methyldopa and in renin, heart rate, and systolic and diastolic pressure with propranolol. Overall, the adrenergic responses to exercise win methyldopa and propranolol were biochemically altered rather than functionally impaired. The latter is related to dose and the underlying age and state of health of our subjects. Methyldopa (or clonidine) may be useful in patients with hypertension who exercise and are predisposed to pertubations in potassium disposition.