In the present study, we evaluated the toxicities of doxorubicin (ADR) in chick embryos using electrocardiograms (ECGs). The influences of the lighting schedule on the toxicities of ADR were then studied in these embryos. Fertilized eggs of White Leghorns were incubated and investigated on two occasions under a constant-light condition and a constant-dark condition. ADR (125, 250, 500 and 1000 ƒÊg) was injected into the air sac of each fertilized egg on the 16th day of incubation. ECGs were recorded after the injection.
Under the constant-dark condition, the lowest dose of ADR showed the maximum increase in the heart rate (HR). The HR decreased relative to the dose of ADR. Arrhythmias were induced at the highest dose. In contrast, no significant changes were observed with any doses except at 1000 ƒÊg under the constant-light condition. The effects of 1000 ƒÊg were similar to those under the constant-dark condition.
These findings indicate that the manipulation of the lighting schedule has a marked influence on the toxicity of ADR in chick embryos.
Key words: doxorubicin, chronopharmacology, lighting schedule, electrocardiograms, chick embryos.