A comparison of the inotropic effects of dopamine and epinine in human isolated cardiac preparations.

The positive inotropic effects of epinine and dopamine have been studied in isolated preparations obtained from human heart in the absence and in the presence of the selective beta adrenoceptors antagonists practolol and ICI 118,551. ED50 values of the two agonists were similar (about 3 x 10(-5) M). The inotropic efficacy of epinine was significantly higher than that of dopamine in adult ventricular and papillary muscles, it was similar to that of dopamine in juvenile myocardial preparations and in adult atria and pectinate muscles. The dopamine-evoked response was significantly more sensitive to practolol than epinine-evoked response, but it was less sensitive to ICI 118,551. pA2 values of practolol and ICI 118,551 were considerably different with epinine but not with dopamine as agonist. The results indicate that, compared to dopamine in isolated human heart preparations, epinine was more potent at beta-2 relative to beta-1 adrenoceptors.