The development of a radioimmunoassay for cannabinoids in blood and urine

Abstract

Abstract Antibodies, for use in radioimmunoassay, have been raised in sheep by immunization with a conjugate of Δ9-tetrahydrocannabinol hemisuccinate and bovine serum albumin. Antiserum titre and avidity were increased by successive booster doses of conjugate. The high degree of non-specific binding encountered in the radioimmunoassay of cannabinoids was reduced by the use of the solubilizing detergent Triton X-405 and by restricting protein concentration in the assay medium. Plasma samples were deproteinized with ethanol before assay, but urine was directly assayed. High avidity antibodies and high specific activity [3H]- Δ9-tetrahydrocannabinol permitted the detection of 50 pg of cross-reacting cannabinoids–-a sensitivity of 7.5 ng ml−1 of plasma and 1.0 ng ml−1 of urine. Whilst apparently specific for the three-ringed cannabinoid nucleus, the assay antiserum cross-reacted with several cannabinoids, both natural compounds and metabolites. Partial identification of cross-reacting cannabinoids was achieved by the use of pure compounds and by the assay of plasma and urine samples collected from rabbits given pure cannabinoids intravenously.