Corticotropin-releasing hormone (CRH) was isolated from the brain of the European green frog, Rana esculenta, by combining HPLC purification with radioimmunoassay (RIA) detection. The amino acid sequence SEEPPISLDLTFHLLREVLEMARAEQIAQQAHSNRKLMDII was identical with the sequence of bullfrog (R. catesbeiana) CRH that was deduced from a cDNA encoding the CRH precursor. Synthetic frog CRH enhanced the release of thyroid-stimulating hormone (TSH) from dispersed bullfrog pituitary cells in a concentration- dependent manner. The TSH-releasing activity of a bullfrog hypothalamic extract was decreased by approximately 45% in the presence of the CRH receptor antagonist, α-helical CRH9-41, suggesting that CRH is one of the main TSH-releasing factors present in the bullfrog hypothalamus.
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