Influence of the light schedule on the toxicity of amitriptyline in chick embryos

The cardiac toxicity of amitriptyline and the effect of the light schedule on it were studied in chick embryos. Fertilized eggs of White Leghorns were incubated under dark conditions and investigated, on two occasions, in the light phase and in the dark phase. Amitriptyline was injected into the air sac of fertilized eggs on the 16th day of incubation. Electrocardiograms were recorded 0 to 60 min after the injection. After the administration of amitriptyline 1 mg/egg in the light phase, the heart rate did not differ compared with that in controls. However, the heart rate was significantly decreased by the administration of amitriptyline 2.5 mg/egg and 5 mg/egg in the light phase. The heart rate was significantly decreased by the administration of amitriptyline 1 mg/egg under dark conditions. In addition, arrhythmia was produced by the administration of amitriptyline under dark conditions. These findings indicate that manipulation of the light schedule has a marked influence on the toxicity of amitriptyline in chick embryos.