Photoperiod and temperature effects on adrenal tyrosine hydroxylase and its relation to nonshivering thermogenesis.

Exposure to short photoperiod increased the activity of adrenal tyrosine hydroxylase (TOH). During summer, the shortening of photoperiod at constant Ta of 23 degrees C stimulated TOH from 7.28 to 10.94 nmoles L-Dopa (h . pair of adrenals), which was as effective as a chronic exposure to 15 degrees C Ta, elevating TOH to 9.1 nmoles L-Dopa/(h . pair of adrenals). The stimulation of TOH by photoperiod or cold exposure in Djungarian hamsters was well correlated with an increase in their ability for nonshivering thermogenesis.