Thyrotropin-Releasing Hormone: Abundance in the Skin of the Frog, Rana pipiens

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Abstract
Thyrotropin-releasing hormone, a hypothalamic tripeptide that stimulates the secretion of pituitary thyroid-stimulating hormone in mammalian species and is widely distributed throughout the brain of vertebrates, is present in the skin of the frog (Rana pipiens) in concentrations twice that found in the hypothalamus of this amphibian. A skin extract shows biologic activity appropriate to its immunoreactive content. Apart from the brain and spinal cord, immunoreactive thyrotropin-releasing hormone is found only in the blood and retina in significant concentrations. The results imply that frog skin is a huge endocrine organ that synthesizes and secretes this hormone.