The toxicological and pharmacological effects of xanthine derivatives, caffeine, theophylline and then bromine were investigated using chick embryos. The drugs were each injected into the air sac of fertile eggs on the 2, 5, 8 or 16th day of incubation and LD50 values were determined from the number of the dead embryos on the 18th day of incubation. LD50 values of drugs were more higher in the late stages of incubation. The strength of toxicity was arranged in order of theobromine>caffeine>theophylline, regardless the injection ages. The LD50 values of these drugs in ICR mice i.v. route were also determined and compared with those in chick embryos. However, no good correlation was obtained from LD50 values between two animals.
Furthermore, we evaluated the effects of these drugs on the electrocardiogram tracings of chick embryos. When xanthine derivatives were injected into the air sac of fertile eggs on the 16th day of incubation, theophylline and caffeine increased as that of mammals. The effect of theobromine was different in comparison with that of other drugs.
In conclusion, lethal toxicity of xanthine derivatives in mammals which may be due to a central nervous systemic action could not predict from data of chick embryos. The heart rate of the 16th-day embryos were increased by pharmacological action which may be due to peripheral action of xanthine derivatives. From these facts, chick embryos may be very useful as an alternative animal to obtain the pharmacological effects of cardiovascular drugs.
Key words: xanthine derivatives, electrocardiogram, chick embryo, lethal toxicity, arrhythmia.