Thyrotropin-releasing hormone receptor (TRHR) has already been cloned in mammals where thyrotropin-releas-inghormone (TRH) isknowntoactasapowerful stimulator of thyroid-stimulating hormone (TSH) secretion. The TRH receptor of amphibians has not yet been characterized, although TRH is specifically important in the adaptation of skin color to environmental changes via the secretion of a-melanocyte-stimulating hormone (a-MSH).