Feeding behavior modifies the circadian variation in RR and QT intervals by distinct mechanisms in mice.

Rhythmic feeding behavior is critical for regulating phase and amplitude in the ≈24-h variation of heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding modified the phase and amplitude of 24-h rhythms in RR and QT intervals, and core body temperature to realign with the new feeding time. Changes in core body temperature alone could not account for changes in phase and amplitude in the ≈24-h variation of the RR intervals. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that changes in the phase and amplitude of 24-h rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, changes in QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed that the daily variation in QT interval, but not RR interval, primarily reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate phase and amplitude in RR and QT intervals, respectively.NEW & NOTEWORTHY We used time-restricted feeding and thermoneutrality to demonstrate that different mechanisms regulate the 24-h rhythms in heart rate and ventricular repolarization. The daily rhythm in heart rate reflects changes in autonomic input, whereas daily rhythms in ventricular repolarization reflect changes in core body temperature. This novel finding has major implications for understanding 24-h rhythms in mouse cardiac electrophysiology, arrhythmia susceptibility in transgenic mouse models, and interpretability of cardiac electrophysiological data acquired in thermoneutrality.