1998 Volume 21 Issue 4 Pages 408-410
In vitro binding characteristics of Δ8-tetrahydrocannabinol (Δ8-THC) and its metabolites, 11-hydroxy-Δ8-THC (11-OH-Δ8-THC) and 11-oxo-Δ8-THC, as well as an inactive metabolite, Δ8-THC-11-oic acid, as a cannabinoid receptor site from bovine cortex were examined using the specific agonist [3H]CP-55940. 11-OH-Δ8-THC and 11-oxo-Δ8-THC strongly inhibited the specific binding of [3H]CP-55940. The Ki values of 11-OH-Δ8-THC and 11-oxo-Δ8-THC for the specific binding of [3H]CP-55940 were 52 and 143 nM, respectively, whereas that of Δ8-THC-11-oic acid was 917 nM. Scatchard plot analyses indicated that 11-OH-Δ8-THC and 11-oxo-Δ8-THC caused a significant increase in the apparent KD value without changing the apparent Bmax. These results reveal that active metabolites of Δ8-THC also competitively bind to the cannabinoid receptor as agonists.