title: Thyroxine and reverse T3 5'deiodination in the cells of human adipose tissue.
abstract: The intracellular 5'deiodination (5'D) of T4 and rT3 has been investigated in human adipose tissue. We studied 5'D in intact adipose tissue, its morphological components and in 3T3-L1-cells. 5'D as assessed by T3-production out of T4 and by rT3-decomposition was not inhibited by propylthiouracil (PTU), but by iopodate (IOP). The apparent Michaelis constants were kM = 3 nM for rT3 and kM = 1 microM for T4. The rT3-degradation was linear over 25 h (115 pg/h.mg (prot.)) both at 37 degrees C and at 4 degrees C. The same type of 5'D was observed in adipocytes, stromal-vascular cells and in 3T3-L1-cells regarding T4 to T3 degradation (244 +/- 30, 181 +/- 27, 227 +/- 37 pg T3/mg.min), resp.; PTU did not exert any influence upon 5'D in the cells investigated. We conclude, that i. the intracellular generation of T3 in adipose tissue does not derive from type I deiodination; ii. 5'D in adipocyte precursors and differentiated adipocytes is identical and iii. there is no difference between human cells and 3T3-L1-cells regarding 5'D.
authors.affiliation: Abt. Innere Medizin I, Medizinische Klinik, Universität Ulm, Donau, Germany.
authors.forename: C F
authors.initials: CF
authors.lastname: Wolf
authors.forename: F S
authors.initials: FS
authors.lastname: Keck
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation; D006801:Humans; D066298:In Vitro Techniques; D007487:Ipodate / Q000494:pharmacology; D007700:Kinetics; D011441:Propylthiouracil / Q000494:pharmacology; D013974:Thyroxine / Q000378:metabolism*; D014285:Triiodothyronine, Reverse / Q000378:metabolism*
chemical_list: D014285:Triiodothyronine, Reverse; D011441:Propylthiouracil; D007487:Ipodate; D013974:Thyroxine