Influence of the light schedule on the toxic interaction between propranolol and disopyramide in chick embryos.

The effect of the light schedule on toxic interactions between propranolol and disopyramide were studied in chick embryos. Fertilized eggs of White Leghorns were incubated under dark conditions and investigated, on two occasions, under light conditions or under dark conditions. Propranolol, with and without disopyramide, was injected into the air sac of fertilized eggs on the 16th day of incubation. Electrocardiograms (ECGs) were recorded 0 to 60 min after the injection. After the injection of propranolol with disopyramide, the heart rate was significantly decreased compared with the injection of propranolol alone under light conditions. In addition, this toxic interaction between propranolol and disopyramide was more severe under dark conditions than under light conditions. These findings indicate that manipulation of the light schedule has a marked influence on the toxic interaction between propranolol and disopyramide in chick embryos.