Effects of selective dopaminergic receptor stimulation on ventricular remodeling after experimental myocardial infarction in rats

Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects

Apomorphine (Apo), a dopaminergic agonist used for treatment of Parkinson disease, is a potent antioxidant. In addition to its antioxidative effects, the dopaminergic and adrenergic effects of Apo were studied. Isolated perfused rat hearts were exposed to 25 min of no-flow global ischemia (37 degrees C) and 60 min of reperfusion (I/R, control). Drugs were introduced for the first 20 min of reperfusion. The LVDP of the control group recovered to 54.6 +/- 3.3%. Apo-treated hearts had significantly improved recovery (61.6 +/- 5%, p < 0.05). The recovery of the work index LVDP x HR was even bigger: 67.8 +/- 3.7% (Apo treatment) vs 41.7 +/- 4.6% (control, p < 0.001). Haloperidol, a dopaminergic antagonist, did not affect the recovery with Apo. Propranolol, a beta-adrenergic blocker, initially inhibited the effect of Apo. However, the recovery of the combined group (Apo + propranolol) increased and reached significance (LVDP, p < 0.05 vs control group) after cessation of propranolol perfusion. At 60 min of reperfusion this group was superior to Apo-treated hearts (LVDP, p < 0.05). Propranolol (without Apo) did not improve the hemodynamic recovery. The same pattern of recovery applies also to the recovery of the +dP/dt during the reperfusion. L-DOPA was less effective than Apo. I/R caused significant increase in carbonylation of proteins. Apomorphine inhibited the increase in carbonylation. Haloperidol did not affect this beneficial effect of Apo. L-DOPA significantly decreased the carbonylation of proteins. We conclude that the antioxidative effect of Apo is its main mechanism of cardioprotection.

Direct vasodilating effects of the new dopaminergic agonist Z1046 in human arteries

Dopaminergic agonists remain of interest in the treatment of heart failure; however, concomitant stimulation of alpha- and beta-receptors should be avoided. This study evaluates the dopaminergic and adrenergic (vasodilating) properties of Z1046, epinine (the active metabolite of ibopamine), and dopamine. Isotonic contraction experiments were performed on human internal mammary artery rings in vitro. alpha1-Antagonistic effects of Z1046 were demonstrated by performing cumulative dose-response curves with the selective alpha1-agonist phenylephrine in the presence of Z1046. Furthermore, both alpha1- and dopamine-mediated receptor effects of Z1046, epinine, and dopamine were studied by performing cumulative dose-response relations both at baseline and in precontracted artery rings both with and without the D1-like antagonist SCH23390. In contrast to both epinine and dopamine, Z1046 is devoid of alpha1-receptor-mediated contraction. Furthermore, Z1046, epinine, and dopamine induced direct dopamine receptor-mediated vasodilation when interfering alpha1 effects were blocked. In contrast to epinine and dopamine, Z1046 is devoid of vasoconstricting properties at higher dosages. Because of its D1-like agonistic and alpha1-antagonistic properties, Z1046 is an effective vasodilator in the whole dosage range. Because of its total receptor profile, Z1046 appears to be more favorable for treatment of heart failure than is ibopamine.