INTERDEPENDENCE OF CORTICOSTERONE-HORMONES AND THYROID-HORMONES IN LARVAL TOADS (BUFO-BOREAS) .1. THYROID HORMONE-DEPENDENT AND HORMONE-INDEPENDENT EFFECTS OF CORTICOSTERONE ON GROWTH AND DEVELOPMENT

In a previous study (Hayes et al. [1993] J. Exp. Zool., 266:206-215), we demonstrated that exogenous corticosterone (B) inhibited growth, an d had varied effects on development and metamorphosis in the toad (Buf o boreas). The current study determined the relation between the actio ns of B and thyroid hormones on body growth (length and weight), tail growth. and reduction (length and height), rear leg growth and differe ntiation, and foreleg emergence (FLE). Thiourea (Thio; a goitrogen) an d metyrapone (MTP; a glucocorticoid synthesis inhibitor) were used to determine the role of endogenous hormones in growth and development. T hese inhibitors were also used in various combinations with the thyroi d hormones, thyroxine (T-4) and triiodothyronine (T-3), to determine t he extent to which B's actions depend on the thyroid hormones. B was i neffective at inducing tail reduction (length and height) in the prese nce of Thio, but B enhanced the effects of both thyroid hormones, sugg esting that the actions of B on the tail were dependent on thyroid hor mones. B inhibited body growth even in the presence of Thio, but did n ot enhance thyroid hormone's inhibition of growth. B alone stimulated foreleg emergence (FLE) and enhanced thyroid hormone's activity on FLE when B and the thyroid hormones were given in combination, but did no t induce FLE in the presence of Thio. B stimulated rear leg developmen t, but not in the presence of Thio, suggesting that this effect was du e to interactions with thyroid hormones. Furthermore, MTP antagonized the stimulatory effect of T-4 on rear leg development, suggesting that endogenous B also interacted with exogenous thyroid hormones. While t he thyroid hormones stimulated rear leg growth, B inhibited rear leg g rowth and antagonized the effects of the thyroid hormones when the hor mones were given together. This study demonstrated that while same of the effects of B (such as the stimulation of tail resorption) depend o n endogenous thyroid hormones, other effects (such as the inhibition o f rear leg growth) are antagonistic to the thyroid hormones. (C) 1995 Wiley-Liss, Inc.