Comparison of effects of marihuana cigarettes to three different potencies.

Marihuana cigarettes containing 1.32%, 1.97%, and 2.54% delta 9-tetrahydrocannabinol (THC) were smoked by six experienced marihuana users at weekly intervals in a double-blind cross-over design under laboratory conditions. Puff duration, number of puffs taken, duration of inhalation holding, interval between puffs, and duration of smoking were recorded for each cigarette smoked. The portion of each cigarette remaining after smoking was weighed and analyzed to determine THC content. Subjective ratings of the "high" achieved and the heart rate acceleration induced by smoking the marihuana were measured. The plasma concentrations of THC and of its principle metabolite, 11-nor-delta 9-THC-9-carboxylic acid (9-carboxy THC), were determined by radioimmunoassay of blood samples drawn at frequent intervals for 6 hr. The results indicate that, irrespective of the potency of the marihuana, the pattern of smoking was much the same. The magnitude of the subjective high, heart rate acceleration, THC, and 9-carboxy THC plasma concentrations were proportional to potency. This dose response was particularly clear between the 1.32% and the 2.54% cigarettes. Peak plasma concentrations of THC consistently occurred 7 to 8 min after initiation of smoking and declined thereafter despite continued smoking for another 6 to 10 min. Peak subjective high and peak heart rate acceleration occurred several minutes after the end of smoking and at a considerable interval after maximal THC plasma concentrations were reached.

Radioimmunoassays for cannabinoids.

The simplicity, sensitivity, and specificity of radioimmunoassay have made it an attractive procedure for the analysis of delta-9-tetrahydrocannabinol (THC) in biological fluids or tissues. The presence of closely related compounds such as metabolites may interfere with radioimmunoassay results. Appropriate design of immunogens may diminish such interference. This work has been directed towards the use of the amyl side chain for linking cannabinoid compounds to proteins to form immunogens. Although the amyl side chain is metabolized to some extent, the metabolites are not quantitatively significant in most cases. 5'-Carboxy-delta-8-THC and 5'-carboxy-delta-9-THC were linked to bovine serum albumin. Immunization of rabbits with the resulting conjugates resulted in the formation of antisera with high selectivity for delta-9-THC vs. its carboxylic acid metabolite, 11-nor-9-carboxy-delta-9-THC. Delta-8-THC radioligands (4',5'-tritium and 5'-iodine-125) could be used with these antisera for analysis of delta-9-THC in plasma. Sensitivity with tritium-labeled material is about 2.5 ng/ml. 5'-Oxo-11-nor-9-carboxy-delta-8-THC was used to prepare an immunogen which led to the generation of an antiserum highly specific for 11-nor-9-carboxy-delta-9-THC. This antiserum and iodine-125-5'-iodo-11-nor-9-carboxy-delta-8-THC were used to develop a highly specific assay for 11-nor-9-carboxy-delta-9-THC in plasma.