Ki: 12 nM (μ-opioid receptor)
Adrenorphin (Metorphamide) is a opioid octapeptide from bovine brain, acts as a potent agonist of μ-opioid receptor, with K i of 12 nM. The binding ratios of K i for μ-opioid receptor/K i for δ-opioid receptor of 0.04 and of K i for μ-opioid receptor/K i for κ-opioid receptor of 0.46. Adrenorphin potently inhibits catecholamine secretion evoked by 10 μM nicotine in cultured human pheochromocytoma 6 cells, with an IC 50 of 1.1 μM.