Cardiovascular effects of ritodrine are blocked by metoprolol in the anesthetized dog.

Inhibition of ritodrine-induced cardiac and peripheral vascular effects by the beta 1-adrenergic blocker metoprolol, was studied by electromagnetic flow measurements in anesthetized dogs. As expected, metoprolol inhibited the ritodrine-induced/increased cardiac workload and heart rate. Metoprolol also inhibited ritodrine-induced peripheral vasodilation. This leads to questions about the cardiac beta 1-adrenergic selectivity of metoprolol. Regarding earlier studies showing no interference in labor inhibition, the combination of ritodrine and metoprolol might be useful in treatment of preterm labor, while economizing cardiovascular performance centrally as well as peripherally.