Effects of ibopamine on exercise-induced increase in norepinephrine in normal men.
The effects of 100 mg ibopamine, an orally active aselective dopamine (DA) agonist, on plasma catecholamines was evaluated in 8 healthy men during sympathetic stimulation by graded exercise in a single-blind, placebo-controlled cross-over study. The exercise consisted of progressive cycling activity less than or equal to 90% of the previously determined VO2max. Graded exercise resulted in an increase in systolic and mean blood pressure (SBP, MBP), heart rate, norepinephrine (NE) and epinephrine level, with a decrease in diastolic BP (DBP). The increase in NE was significantly blunted by ibopamine as compared with placebo. No differences for BP, heart rate (HR), or epinephrine between placebo- and ibopamine study day were noted. In previous studies, ibopamine decreased resting plasma NE in patients with congestive heart failure (CHF), whereas plasma NE was not altered by ibopamine in healthy volunteers. This different outcome in both categories might therefore be explained by the absence of substantial sympathetic stimulation in normal humans at rest. Because it is reasonable to assume that the effect of ibopamine on systemic and local hemodynamics is negligible as compared with the effect of exercise in the healthy volunteers, the plasma decrease caused by ibopamine is probably related to stimulation of DA2-receptors. In conclusion, ibopamine blunts the increase of plasma NE during graded exercise in healthy men.