Dynorphin A (1-8) is the predominant opioid peptide identified in placental tissue extracts. Dynorphin A (1-8) is the most likely natural ligand of the kappa receptor. The binding of 3H-Bremazocine to the purified kappa receptor is inhibited by Dynorphin A (1-8) (IC50=303 nM).

Rasarfin inhibits Ras and ARF6.

β-Endorphin, rat (β-Lipotropin 61-91), a neuropeptide, is involved in cardiovascular regulation. β-Endorphin, rat induces marked, prolonged muscular rigidity and immobility similar to a catatonic state in rats.