The Kinetics of Cannabinoid Distribution and Storage With Special Reference to the Brain and Testis

Male and female rats were given either single or repeated intramuscular injections of 2 microCi of 14C-delta 8-tetrahydrocannabinol. They were sacrificed by groups of three at regular intervals 2, 3, 4, 6, or 24 hours after the last injection. Samples of blood lung, brain and pituitary, spleen, liver, fat, testis, and ovary were removed. Some samples were pyrolysed in an automatic oxygen train system to measure 14C-CO2, which reflects total cannabinoid concentration; other samples were kept for measurements of individual cannabinoids after extraction. After a single administration of 14C-delta 8-THC, maximal concentration of total radioactivity was reached in the brain between 2 and 4 hours amounting to 6 ng/gm tissue, or 0.06 per cent of the administered dose. After two weeks of chronic administration, concentrations of radioactivity progressively increased in liver and neutral fat, while cannabinoid levels in brain and testis remained unchanged. These data illustrate the efficiency of the blood-brain and blood-testicular barrier in limiting the access and accumulation of cannabinoids in these tissues.