Table 3.

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

compd	α−1A Ki ± SEM (nM)	α−1B Ki ± SEM (nM)	α−1D Ki ± SEM (nM)	α−2A Ki ± SEM (nM)	α−2B Ki ± SEM (nM)	α−2C Ki ± SEM (nM)
WB 4101b	0.16	0.038	ND	ND	ND	ND
prazosin	ND	ND	0.17 ± 0.03	ND	ND	ND
yohimbineb	ND	ND	ND	3.13	1.16	0.80
corynantheidine	ND	ND	41.7 ± 4.7	ND	ND	ND
mitragynine	1340 ± 100	4770 ± 120	5480 ± 540	4720 ± 120	9290 ± 30	2320 ± 140

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

^bThese data points were conducted once; studies are still ongoing with other kratom alkaloids and the test controls will be repeated.