**β-Adrenoceptor agonists: Dopamine and dobutamine**

Albeit at least three distinct beta-adrenoceptors exist in IMA [105], β -receptor function is weak [31]. Consequently, it has been demonsted that use of β -adrenoceptor agonists is unlikely relax the IMA significantly [106]. Same study also indicated that beta-receptor agonist dobutamine exerts weak vasodilator effect in IMA. Dopamine-induced responses are complex and dosedependent, inasmuch as the complexity of interaction between dopamine and dopamine receptors as well as α1-adrenoceptors [107]. In IMA, dopamine induced a vasorelaxation on the norepinephrine contraction only at higher concentrations [107]. Similar to VEGF, the use of dopamine and dobutamine may not be the primary consideration for antispastic therapy. On the other hand, vasodilator effect of β-adrenoceptor agonists in IMA at high concentrations should be kept in mind when these agents are used primarily as inotropic agents.
