title: Thyroid hormones regulate hepatic glycogen synthase.
abstract: Short term (48 h) in vivo administration of either T3 or T4 was associated with an increase in hepatic glycogen synthase activity in the rat. Administration of 0.25 mg T3/kg BW 48, 24, and 2 h before enzyme preparation increased the total glycogen synthase activity by approximately 50% and increased the percentage of synthase in the I or active form from 19 +/- 1% to 63 +/- 3%. These effects of thyroid hormones on glycogen synthase were rapid (expressed within 24 h) and dose dependent with respect to T3 or T4. Fasting rats for 24 h increased hepatic glycogen synthase levels in control but not thyroid hormone-treated rats. Total glycogen synthase activity of rats administered thyroid hormone and fasted for 24 h remained 1.4-fold greater than that of their fasted euthyroid controls. The percentage of synthase in the I form was 79 +/- 4% for the fasted T3-treated rats compared to 51 +/- 2% for their fasted euthyroid counterparts. Thus, both total hepatic glycogen synthase activity and the percentage of synthase in the I form are increased by short term administration of thyroid hormones in vivo.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005215:Fasting; D005260:Female; D006006:Glycogen Synthase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000502:physiology*; D013997:Time Factors; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D006006:Glycogen Synthase