Photoperiodic control and effects of melatonin on nonshivering thermogenesis and brown adipose tissue.

Exposure to a short photoperiod improved the thermogenic capacity, and cold resistance of Djungarian hamsters and increased the respiratory power of their brown adipose tissue. Exposure to a long photoperiod caused a decrease in thermogenic measurements. This thermotropic action of the short photoperiod was detectable only during late summer and fall. A similar thermotropic response could be elicited by implanting hamsters with melatonin, indicating that the pineal may be involved in photoperiodic control of thermoregulatory effectors.