Original paper :AATEX 6(1):58-64,1999
The pharmacological effects of Ca channel blockers on electrocardiogram (ECG) in the chick embryonic-heart were investigated under different lighting conditions. The fertile eggs of White Leghorn chickens were incubated in dark conditions and used on day 16 of incubation. Three different types of Ca channel blocker, nicardipine, diltiazem and verapamil were injected into the air sac of the fertile eggs under light conditions (450 Lux) or dark conditions (12 Lux). The bipolar lead of ECG patterns was recorded using ECG systems. Heart rates (HRs) were calculated from R-R intervals. Under light conditions, 3 kinds of Ca channel blockers caused a decrease in HRs in a dose-dependent manner and also arrhythmia was provoked. These phenomena were observed more clearly under dark conditions. Furthermore, these enhancements of the drug effects under dark conditions were also observed by concomitant injection of 15-50ƒÊg/egg of melatonin even under light conditions. In conclusion, these results suggest that chick embryos are very useful models for investigating the chronopharmacological effects and for evaluating drug interaction of cardiovascular drugs.
Keywords: Ca channel blocker, chick embryo, electrocardiogram, chronopharmacology, melatonin