MK-0557 是一种选择性口服神经肽 Y5 受体拮抗剂 (Ki: 1.6 nM)。

Neuropeptide FF receptor agonist (Ki values are 48.4 and 12.1 nM for NPFF1 and NPFF2, respectively). Potentiates the antinociceptive action of morphine in vivo and reverses the loss of morphine potency in tolerant animals. Also increases the amplitude of the sustained current of heterologously expressed acid sensing ion channel 3 (ASIC3) (EC50 ~ 50 μM).

Potent, non-selective galanin receptor antagonist (Ki values are 1.82 and 5.1 nM at GAL1 and GAL2 respectively) that inhibits galanin (1-29) binding in rat brain in vitro (IC50 = 3 - 15 nM). Attenuates the antidepressant effects of fluoxetine and blocks galanin-induced food intake in vivo. Also exhibits weak partial agonist activity at peripheral GAL2 receptors at doses > 100 nM.