Corticotropin-releasing factor (CRF), recently isolated from sheep hypothalami, has been shown to stimulate secretion of ACTH and B-endorphin in vitro, and in vivo in rat and man. In previous reports, responses to ovine CRF were studied in heterologous bioassay systems where the ovine sequence was likely to act as a CRF analogue. We administered synthetic ovine CRF to sheep to assess the dynamics of endorphin and cortisol responses. Graded doses of CRF caused a rapid increase in immunoreactive β-endorphin (iB-E) within 2 min of iv administration, followed by a cortisol response which was maximal 15 min after the iB-E peak. Doses of CRF in excess of 10 μg did not increase the magnitude of the peak iB-E response but did prolong the duration of the plasma β-endorphin rise. Ovine CRF is an extremely potent and rapidly-acting hypothalamic peptide in vivo when assayed in a homologous system.

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