Manipulation of the lighting schedule can modify the pharmacological effects of theophylline in chick embryos

The effect of the lighting schedule on the pharmacological action of theophylline was studied in chick embryos. Fertile eggs of White Leghorns were incubated and investigated, on two occasions, under constant light conditions or under constant dark conditions. A single injection of theophylline 2.14, 4.29, 8.57 and 17.14 mg/egg into the air sac of fertile eggs was carried out on the 16th day of incubation. Electrocardiograms (ECGs) were recorded 0 to 60 min after drug injection. After drug injection, heart rate increased under constant light conditions, but decreased under dark conditions. In addition, arrhythmia was produced by theophylline, 17.14 mg/egg, under constant dark conditions. These results indicate that the manipulation of the lighting schedule may have a marked influence on the pharmacological effects of theophylline in chick embryos.