Table 2.

Affinities (K_i ± SEM nM) of Kratom Alkaloids in Specifically Binding to Opioid Receptors As Well As Subtype Selectivity^a

compd	DOP Ki ± SEM (nM)	KOP Ki ± SEM (nM)	MOP Ki ± SEM (nM)
DAMGO	ND	ND	0.41 ± 0.04
DPDPE	1.320 ± 0.004	ND	ND
U50,488	ND	0.300 ± 0.002	ND
corynantheidine	ND	1910 ± 50	118 ± 12
9-hydroxycorynantheidine	ND	ND	105 ± 1
mitragynine	ND	198 ± 30	161 ± 10
7-hydroxymitragynine	236 ± 6	74.1 ± 7.8	7.16 ± 0.94
speciociliatine	ND	116 ± 36	54.5 ± 4.4

^aND: Not determined because there was less displacement of radioligand at 10,000 nM of test compound (Table 1).