The effects of triiodothyronine (T-3) on heart rate, temperature and ECG measured with telemetry in freely moving mice

We have set up a telemetry system and recorded heart rate, electrocardiogram (EGG), body temperature and the locomotor activity in awake freely moving mice. The telemetry system (DATA Sciences, St Paul, MN, USA) comprises a transmitter implanted in the peritoneal cavity and a receiver (RA1010) placed underneath the home cage. The signal from the transmitter includes the electrical activity of the heart and the body temperature. The results show that four days after the surgical procedure the mice have recovered and regained a clear circadian rhythm. The heart rate varied under baseline conditions between 432 and 618 beats min(-1) and the body temperature between 35.1 and 37.7 degrees C (based on 60 min mean values). A clear time correlation between heart rate, body temperature and locomotor activity was found. As an evaluation of the method we injected T-3 s.c. during a period of 4 days. Further, we were interested in whether it was possible to measure an integrated physiological response to T-3 and further investigate the time course for the effect. After one day of treatment with triiodothyronine there was a significant increase in body temperature and locomotor activity. The increase in heart rate was seen after 2 days. The ECG recording revealed a significantly shortened QT(end)- and QRS-time. No significant difference in the PQ-time was found. This method may be of great importance in studies of genetically manipulated mice.