title: Thyroid hormone action on skin: diverging effects of topical versus intraperitoneal administration.
abstract: Previously, we demonstrated stimulation of epidermal proliferation and hair growth in triiodothyronine (T(3)) treated mice. To distinguish skin effects of directly applied T(3) from those of systemic hyperthyroidism, we treated CD-1 mice with either intraperitoneally (IP) or topically administered T(3). Relative to controls, mice receiving T(3) IP had 10% thinner epidermis (p < 0.01) and 48% fewer hairs (p < 0.001). By contrast, mice receiving T(3) topically had 78% thicker epidermis (p < 0.01) and 160% more hairs (p < 0.01). To gain insight into factors responsible for the diverging effects, we contrasted T(3) effect on proliferation of isolated keratinocyte cultures versus keratinocytes cocultured with dermal fibroblasts. For keratinocytes grown in the absence of fibroblasts, T(3) stimulated proliferation in a dose-dependent, biphasic pattern with the peak at 0.5 nM T(3) (84 +/- 30%, p < 0.05). Paradoxically, T(3) inhibited proliferation of keratinocytes cocultured with fibroblasts, the nadir at 0.1 nM T(3) (34% +/- 4%, p < 0.001). These studies are the first describing divergent effects of IP and topically administered thyroid hormone. The data suggest that while T(3) stimulated keratinocyte proliferation, T(3) also stimulated proliferation inhibitory factor(s) from skin fibroblasts. Insight into the interplay among the competing factors will be important in understanding thyroid hormone regulation of skin physiology.
authors.affiliation: Section of Endocrinology, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA. jsafer@bu.edu
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Safer
authors.forename: Tara M
authors.initials: TM
authors.lastname: Crawford
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Fraser
authors.forename: Michael
authors.initials: M
authors.lastname: Hoa
authors.forename: Swapna
authors.initials: S
authors.lastname: Ray
authors.forename: Tai C
authors.initials: TC
authors.lastname: Chen
authors.forename: Kelly
authors.initials: K
authors.lastname: Persons
authors.forename: Michael F
authors.initials: MF
authors.lastname: Holick
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000963:Antimetabolites; D001973:Bromodeoxyuridine; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005260:Female; D005347:Fibroblasts / Q000187:drug effects; D006801:Humans; D007274:Injections, Intraperitoneal; D015603:Keratinocytes / Q000187:drug effects; D008297:Male; D051379:Mice; D009824:Ointments; D012867:Skin / Q000187:drug effects*; D013963:Thyroid Hormones / Q000008:administration & dosage / Q000494:pharmacology*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology
chemical_list: D000963:Antimetabolites; D009824:Ointments; D013963:Thyroid Hormones; D014284:Triiodothyronine; D001973:Bromodeoxyuridine; D013974:Thyroxine