The presence of a corticotropin-releasing factor (CRF) behaving as a peptide with a molecular weight of about 5000 was established after purification of porcine hypothalamic extracts by gel filtration on Sephadex G-25 and then on Sephadex G-50. Purified CRF stimulated the release of corticotropin (ACTH) in three in vitro systems: isolated rat pituitary quarters, monolayer cultures of dispersed pituitary cells, and superfused pituitary cells on a column. A linear logarithmic dose-response relationship existed between 50 and 200 μg of CRF preparations per ml and the total amount of ACTH released by the superfused pituitary cells. The pituitary ACTH response to CRF in the pituitary quarters system was also approximately linearly related to the logarithm of the dose of CRF. CRF also stimulated in vivo release of ACTH in rats pretreated with chlorpromazine, morphine, and Nembutal. CRF activity was labile to digestion with trypsin and chymotrypsin and was partially destroyed by pepsin. The evidence indicates that CRF of porcine origin is a polypeptide of a higher molecular weight than previously assumed.
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