Calcium antagonists and the developing heart.

Ontogenetic differences in cardiac sensitivity to calcium antagonists were studied in chick embryonic and postnatal immature rat heart. It has been found that verapamil exhibits no protective effect on isoprenaline-induced changes of the chick embryonic heart. Furthermore, it increased the mortality of experimental embryos. The mortality of verapamil-treated rats was age-dependent, increasing with decreasing age of animals. Similarly, the intensity of negative inotropic response of the isolated right ventricular myocardium and isolated perfused rat heart was significantly greater in the youngest age groups. These results point to the possible negative consequences of the clinical use of calcium antagonists during the early phases of ontogeny.