Stressin I (Cyclo(31-34)[DPhe12,Nle21,38,Glu31,Lys34]Ac-hCRF(4-41)) TFA is a potent CRF1 receptor selective agonist, Ki is 1.7 nM. Stressin I induces an increase in adrenocorticotropic hormone (ACTH) levels in rats.