title: Interdependence of corticosterone and thyroid hormones in toad larvae (Bufo boreas). II. Regulation of corticosterone and thyroid hormones.
abstract: Typically, the role of corticosterone(B) in metamorphosis is considered secondary to that of thyroid hormone, with B having only enhancing effects. In the current study, we demonstrate that the relationship between the thyroid hormones and B is much more complex and that thyroxine (T4) may depend on B for some of its functions. Tadpoles of the western toad (Bufo boreas) were treated with various combinations of corticosterone (B), thyroxine (T4), triiodothyronine (T3), a goitrogen (thiourea; Thio), and a corticoid synthesis inhibitor (metyrapone; MTP). Hormones were extracted from individual tadpoles and whole-body hormone levels determined by radioimmunoassay. B-treatment decreased the ratio of T4 to T3, suggesting that B increased the conversion of endogenous T4 to T3. In addition, B-treatment in combination with T4 resulted in high whole body-levels of T3. B also caused a decrease in whole body-thyroid hormone levels (T4 and T3), suggesting negative feedback on the hypothalamo-pituitary-thyroid axis and T3 had a similar effect, decreasing whole body-T4 levels. T4-treatment, but not T3, increased whole body-B levels and MTP-treatment in combination with T4 prevented the stimulatory effect of T4 on B production. MTP-treatment alone blocked all steroid metabolism of [3H]progesterone by the inter-renal in vitro, and lowered whole body-B levels three-fold in vivo. Thio-treatment reduced thyroid hormone levels and also resulted in decreased B. Finally, we suggest that these results demonstrate a system in which T4 may regulate its own potency: increasing T4 stimulates B production, which increases the conversion of T4 to its more active form T3.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Integrative Biology, University of California, Berkeley 94720.
authors.forename: T B
authors.initials: TB
authors.lastname: Hayes
authors.forename: T H
authors.initials: TH
authors.lastname: Wu
mesh_terms: D000375:Aging / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D002025:Bufonidae / Q000254:growth & development*; D003345:Corticosterone / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D004347:Drug Interactions; D006706:Homeostasis; D007814:Larva; D008675:Metamorphosis, Biological / Q000187:drug effects; D008797:Metyrapone / Q000494:pharmacology; D008954:Models, Biological; D011863:Radioimmunoassay; D013890:Thiourea / Q000494:pharmacology; D013974:Thyroxine / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D014284:Triiodothyronine / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D014284:Triiodothyronine; D013890:Thiourea; D013974:Thyroxine; D003345:Corticosterone; D008797:Metyrapone