Table 2. Inhibitory Effects of GPR54 Agonists on Radioligand Binding to Neuropeptide FF Receptors (NPFFRs).

	IC50 (M)
peptide	GPR54a	NPFFR1b,c	NPFFR2b,c
Kp-54	−d	1.5 × 10−8	4.0 × 10−7
Kp-10	1.2 × 10−10	4.7 × 10−9 (39)	7.6 × 10−8 (630)
FTM080 1	7.1 × 10−10	1.6 × 10−7 (230)	1.8 × 10−6 (2500)
FTM145 2	1.2 × 10−10	6.4 × 10−7 (530)	2.4 × 10−6 (20000)
neuropeptide SF	>3.0 × 10−5	1.9 × 10−9	7.9 × 10−10

^aIC₅₀ values indicate the concentration needed for 50% inhibition of receptor binding of [¹²⁵I]kisspeptin-15 to GPR54.¹⁶

^bIC₅₀ values indicate the concentration needed for 50% inhibition of receptor binding of (d-[¹²⁵I]Tyr¹, MePhe³)-NPFF to NPFFRs. The data were derived from the dose−response curves generated from triplicate data points.

^cShown in parentheses are the selectivity indexes (SIs) calculated by SI = IC₅₀(NPFFR)/IC₅₀(GPR54).

^dNot tested.