Control of norepinephrine turnover in brown adipose tissue of Syrian hamsters
Sigurdson, S.L.; Himms-Hagen, J.
American Journal of Physiology 254(6 Pt 2): R960-R968
1988
ISSN/ISBN: 0002-9513 PMID: 3381919 Document Number: 325373
Sympathetic nervous system activity in brown adipose tissue (BAT) of normal and myopathetic Syrian hamsters was assessed by measuring norepinephrine turnover rate (NETR) using [3H]norepinephrine. Acute exposure of normal hamsters to cold (4.degree. C) for 4 or 24 h increased norepinephrine secretion but not resynthesis. By 3 days and at 2 wk in the cold, NETR increased but returned to a normal level by 6 wk. Hamsters were initially hypothermic (to 3 days) then normothermic (2 and 6 wk). Adapatation of normal or myopathic hamsters to high-fat diet or short photoperiod (4 h light, 20 h dark) for up to 12 wk did not alter NETR in BAT. Serum triiodothyronine (T3) concentration increased rapidly in the cold to reach a maximum level by 24 h at which it remained for 6 wk and was not correlated with changes in NETR in BAT. The high-fat diet did not alter T3 level in normal hamsters; it increased the low T3 level in myhopathic hamsters. Short photoperiod induced a transient increase in T3 level in normal hamsters but not in myopathic hamsters. We concldue that the hypertrophied state of BAT in Syrian hamsters adapated to cold, to high-fat diet, or to short photoperiod is not maintained by elevated norepinephrine secretion and that some other factor(s) must be involved. A selective increase in concentration of BAT mitochondrial uncoupling protein in hamsters may be dependent on raised T3 level in serum and/or production in BAT, since both occur in response to cold acclimation but not in response to high-fat diet or short photoperiod.