Day-Night Changes After Exercise in Body Temperatures and Heart Rates of Hamsters

A day-night rhythm of body temperature in the golden hamster (Mesocricetus auratus) is described, showing a maximum of about 37.6°C in the night-animal and a minimum which is about l.3°C lower in the day-animal. The day-night difference is still present after forced exercise, indicating that the temperature-regulating mechanism, rather than muscular activity alone, accounts in part for the observed day-night rhythm of body temperature in the hamster. A day-night rhythm of heart rate was also found with a resting midnight level of 457 beats/min, and a resting noon minimum level which is about 45 beats/min lower. Apparently the hamster has a day-night cardiovascular setting as found in many other mammals. The heart rates decreased after forced exercise, and there was no evidence of the day-night heart rhythm during the period of recovery which extended for several hours