Independence of heart rate and circadian period in the golden hamster.

Abstract

Cardiac contractions are under the influence of at least two processes of biological timing, one responsible for the mean level of heart rate (oscillations with a frequency of up to several hundred per minute) and another responsible for the circadian rhythm of heart rate (oscillations with a frequency of one per 24 h). To investigate whether the mean level of heart rate is proportional to the frequency of circadian oscillation, we compared the heart rates of normal golden hamsters (circadian period approximately 24 h) and tau-mutant hamsters (circadian period approximately 20 h). Neither in anesthetized preparations nor in freely moving animals was there a difference in heart rate between the two groups despite the 20% difference in circadian period. Thus the mean level of heart rate seems to be independent of the circadian period. It is likely that the tau gene, which affects the frequency of the circadian pacemaker, has no effect on the intrinsic frequency of the cardiac pacemaker. In vitro studies of isolated hearts or myocardial cell cultures are necessary to confirm this inference.