Animal experiment:

Mice[2]The Mrp4-/- mice are used. Concerning the PH reversal study, 5-week-old WT mice are maintained in hypoxia for 3 weeks, then are randomized to receive, for 2 weeks, oral vehicle or MK-571 at the doses of either 5 mg/kg/d or 25 mg/kg/d. At the same time, the experiment is designed for mice in normoxia conditions. Increased hematocrit valuesare checked to assess the efficiency of hypoxia[2].

• Curr Drug Deliv 19.4 (2022): 508-517.PMID: 34238184

MK571 sodium salt is a specific CysLT1 (Cysteinyl-Leukotriene Type 1 Receptor) antagonist [1].

Cysteinyl leukotriene receptor 1, also termed as CYSLTR1, is a receptor for cysteinyl leukotrienes (LT)which mediates a large variety of allergic and hypersensitivity reactions in humans [2].

In vitro: MK571 is a multidrug resistance protein-2 (ABCC2, Mrp2) inhibitor and had been widely used to demonstrate the role of Mrp2 in the cellular efflux of drugs, xenobiotics and their conjugates. Apically-applied MK571 resulted in significant reductions in both the apical and basolateral efflux of flavonol conjugates from Caco-2/TC7 monolayers. The estimated Ki for inhibition of the synthesis of K-4′-O-GlcA by MK571 is 19.7 μM. MK571 inhibited the intracellular biosynthesis of all flavonol glucuronides and sulphates by Caco-2 cells in a dose-dependent manner. MK571 significantly inhibited phase-2 conjugation of kaempferol by cell-free extracts of Caco-2, and competitively inhibited the production of kaempferol-4′-O-glucuronide. These data indicated that MK571, in addition to inhibiting MRP2, was a potential inhibitor of enterocyte phase-2 conjugation [3].

References:
[1]. Thivierge M, Turcotte S, Rola-Pleszczynski M, et al. Enhanced cysteinyl-leukotriene type 1 receptor expression in T cells from house dust mite-allergic individuals following stimulation with Der p[J]. Journal of immunology research, 2015, 2015.
[2]. Singh RK, Tandon R, Dastidar SG, Ray A (November 2013). "A review on leukotrienes and their receptors with reference to asthma". The Journal of Asthma. 50 (9): 922–31.
[3]. Barrington R D, Needs P W, Williamson G, et al. MK571 inhibits phase-2 conjugation of flavonols by Caco-2/TC7 cells, but does not specifically inhibit their apical efflux[J]. Biochemical pharmacology, 2015, 95(3): 193-200.