Steroids as Potential Modulators of Thyroid Hormone Activity in Anuran Metamorphosis

SYNOPSIS. Anuran metamorphosis is controlled by the complexinteraction of several hormones. Although thyroid hormone isthe major stimulatory hormone in metamorphosis and likely regulatesall of the metamorphic genes directly, other hormones are involvedin regulating thyroid hormone secretion and activity. Corticoids(in particular corticosterone) and the sex steroids (especially17ß estradiol) all potentially regulate thyroid hormoneactivity both by affecting hypothalamic and pituitary controlof thyroid hormone secretion and by interacting with thyroidhormones peripherally. Although there is likely a role for endogenouscorticoids in anuran metamorphosis, the role for endogenousestrogens remains to be shown. The role of these "modulators"must be fully understood, if our understanding of hormonal controlof metamorphosis is to be complete.