Thyroid hormones and corticoid synergies are critical in many vertebrate life stage transitions.
Corticoids affect the expression of deiodinases and thyroid hormone receptors.
CRH has corticotropic and thyrotropic actions in nonmammalian vertebrates.
CRH may regulate transitions, but only amphibian metamorphosis has been studied in detail.
The available evidence suggests that CRH has lost its thyrotropic activity in mammals.