Tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) 
activities were assayed in adrenal glands of the following groups of the Alaskan 
red-backed vole (Clethrionomys rutilus dawsoni): 1) laboratory reared at 20 
degrees C and 2) exposed to 5 degrees C for 1, 3, 7, and 28 days; 3) wild, 
summer acclimatized; 4) wild, fall acclimatized; and 5) wild, winter 
acclimatized. TH activity in laboratory-acclimated voles exposed to 5 degrees C 
was increased by 2 times after 3 days and remained elevated after 28 days. PNMT 
activity in these same voles was increased after 7 days and also remained 
elevated after 28 days of cold exposure. In wild-acclimatized voles TH activity 
and PNMT activity in summer were equivalent to levels in 28-day cold-acclimated 
laboratory voles. In fall, TH activity was increased to 2.5 times the summer 
value. It decreased by midwinter, but remained elevated above the summer level. 
In contrast, PNMT activity appeared unchanged from summer through fall and 
winter. Pregnant summer voles had markedly increased TH activity. Adrenal 
norepinephrine and epinephrine did not change significantly with cold 
acclimation or seasonal acclimatization. Thus, acclimatization of wild voles to 
fall and winter conditions involved aquisition of a greater capacity to 
synthesize adrenal catecholamines than that produced by exposing 
laboratory-reared voles to an extended period of cold.