COLD-INDUCED CHANGES OF THYROXINE 5'-MONODEIODINASE AND 5-MONODEIODINASE ACTIVITY IN BROWN ADIPOSE-TISSUE OF NEONATAL RABBITS - IMPLICATIONS FOR THERMOGENESIS

1. The neonatal changes in response of the 5'-MD in the BAT, liver and kidney to cold, norepinephrine (NE) and melatonin treatment were dete rmined in 1-14 days old rabbits. 2. The 5'-MD responded to cold from d ay 5 in the BAT, from day 3 in the kidney and did not respond (with ex ception of the day of birth) in the liver. 3. The NE and melatonin cau se a marked, non-relative to age, increase in 5'-MD activity in the BA T, and variable in the liver and kidney. 4. The results indicate that shortly after birth, the BAT 5'-MD has low reactivity to cold although it is highly sensitive to hormones: NE and melatonin.