NH-3 is an orally active, reversible thyroid hormone receptor (THR) antagonist with an IC50 of 55 nM. NH-3, a derivative of the selective thyromi-metic GC-1, inhibits binding of thyroid hormones to their receptor and that inhibits cofactor recruitment[1][2][3].
NH3 (46.2-27,700 nmol/kg/day; 7 days) decreases heart rate modestly starting at 46.2 nmol/kg/day, but the effect was lost at >2920 nmol/kg/day. NH3 has no effect on the cholesterol-lowering action of 46.2 nmol/kg/day T3, but it inhibits the tachycardic and TSH suppressant effects up to the 924 nmol/kg/day dose[2].
[1]. Latika Singh, et al. Chasing the Elusive Benzofuran Impurity of the THR Antagonist NH-3: Synthesis, Isotope Labeling, and Biological Activity. J Org Chem. 2016 Mar 4;81(5):1870-6.
[2]. Gary J Grover, et al. Pharmacological profile of the thyroid hormone receptor antagonist NH3 in rats. J Pharmacol Exp Ther. 2007 Jul;322(1):385-90.
[3]. Wayland Lim, et al. A thyroid hormone antagonist that inhibits thyroid hormone action in vivo. J Biol Chem. 2002 Sep 20;277(38):35664-70.