Thyroid cold acclimation influences on norepinephrine metabolism in brown fat
Kennedy, D.R.; Hammond, R.P.; Hamolsky, M.W.
American Journal of Physiology 232(6): E565-E569
1977
ISSN/ISBN: 0002-9513 PMID: 18013 Document Number: 120768
Female Charles River rats were kept in a room at 4 deg C for 6 weeks. Hyperthyroidism was induced by daily injections of L-thyroxine 1 mg/kg for 6 days. Hypothyroidism was induced by thyroidectomy at 7 weeks old. Norepinephrine turnover rate and tyrosine hydroxylase activity were estimated in the interscapular brown fat pad at the end of each experimental period and at 8 weeks after thyroidectomy. The rate of norepinephrine turnover increased during cold adaptation and hyperthyroidism and fell after thyroidectomy. Tyrosine hydroxylase activity rose during cold adaptation but hyperthyroidism and thyroidectomy had no effect. None of the conditions changed the apparent Km of tyrosine hydroxylase for L-tyrosine. Cold acclimatisation significantly reduced the apparent Km of tyrosine hydroxylase for pterin cofactor; thyroxine and thyroidectomy had no effect.