Excessive plasma dopamine increase at rest and during exercise after long-term beta-adrenoreceptor blockade in hypertensive patients.

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Abstract
The effect of 4 wk and 15 mo. of treatment with the cardioselective .beta.-receptor antagonist metoprolol on blood pressures, plasma noradrenaline [norepinephrine], adrenaline [epinephrine] and dopamine at rest, during submaximal steady state and near maximal exercise, and 5 min after exercise, was studied in 7 moderately hypertensive men aged 25-51 yr. Four weeks of treatment resulted in significantly lower heart rates and blood pressures at rest and during and after exercise; no further significant changes were observed after 15 mo. of continuous treatment. The exercise-induced increase in plasma noradrenaline and adrenaline tended to be more pronounced after treatment with metoprolol with virtually identical value after 4 wk and 15 mo. Plasma dopamine was less affected by exercise and showed a weak tendency towards higher values during work. While no significant changes were observed after 4 wk of treatment, there was a significant 10- to 12-fold increase of dopamine over the control values after 15 mo. treatment. At rest plasma dopamine was 5 and 10 times higher than corresponding noradrenaline and adrenaline levels. The excessive rise of dopamine might have clinical implications: because of the cardiovascular and renal actions of dopamine, high levels should tend towards dampening the negative inotropic effect of .beta.-receptor blockade and might contribute to the increase of cardiac output and decrease of peripheral vascular resistance usually seen with .beta.-receptor antagonists after long-term treatment compared with acute or short-term administration.

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