Distribution and metabolism in vivo of 14C-tetrahydrocannabinol in the rat

Pharmacokinetic factors in sex differences in Δ9-tetrahydrocannabinol-induced behavioral effects in rats

Cannabinoids have been shown to produce greater behavioral effects in female than in male rats. Sex differences in the metabolism of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) have also been demonstrated in one study. The goal of this study was to determine if sex differences in Delta(9)-THC disposition or metabolism could explain sex differences in Delta(9)-THC-induced behavioral effects. [(3)H]-Delta(9)-THC was administered intraperitoneally (i.p.) to rats and the presence of [(3)H]-Delta(9)-THC and metabolites in serum and brain tissue were compared at multiple times post-injection in male versus female rats. Serum levels of Delta(9)-THC and its metabolites were similar in males and females. In brain tissue, [(3)H]-Delta(9)-THC levels also were similar in males and females. In contrast, levels of Delta(9)-THC metabolites in brain tissue, including 11-hydroxy-Delta(9)-THC, the major active metabolite, were higher in females than in males. To further investigate if greater production of active metabolites by females explained the greater Delta(9)-THC-induced behavioral effects observed in females, i.p. Delta(9)-THC-induced antinociception (50 degrees C warm water tail withdrawal assay) and catalepsy (bar test) were compared in male and female rats following pretreatment with saline or SKF525A, a cytochrome P450 inhibitor. SKF525A did not affect basal responding in the tail withdrawal assay or bar test in either sex. SKF525A significantly attenuated Delta(9)-THC-induced antinociception only in females. A similar sex difference was observed in the effects of SKF525A on Delta(9)-THC-induced catalepsy. These results suggest that the greater levels of active Delta(9)-THC metabolites produced by females contribute to greater behavioral effects of Delta(9)-THC in female compared to male rats.

The effect of (-)-trans-delta 9-tetrahydrocannabinol on regional brain levels and subcellular distribution of monoamines in the rat

1. The effect of intravenously injected delta 9-tetrahydrocannabinol (delta 9-THC, 2 mg/kg) on subcellular distribution in the whole brain and the regional brain levels of noradrenaline, dopamine, serotonin and 5-hydroxyindoleacetic acid were determined in the rat. 2. The levels of noradrenaline and dopamine were not altered by delta 9-THC in the hypothalamic, medullary and rest of brain areas, whereas those of serotonin and 5-hydroxyindoleacetic acid were elevated in the medullary and hypothalalmic areas, respectively. 3. delta 9-THC did not alter the levels of these monoamines and the metabolite 10 min after injection; however, there was a shift of dopamine from the bound to the free fraction. On the other hand, there was a shift of 5-hydroxyindoleacetic acid from the free to the bound fraction. 4. After 1 h, there was no difference in the subcellular ratios of noradrenaline, dopamine, serotonin and 5-hydroxyindoleacetic acid were increased. 5. It is suggested that the effects of delta 9-THC may be mediated by modification of the subcellular distribution of dopamine and serotonin.

Residual learning deficit after heavy exposure to cannabis or alcohol in rats

Acute oral administration of cannabis extract to rats (tetrahydrocannabinol dose, 10 milligrams per kilogram) impaired maze learning. The impairment was more marked after ten daily doses of the same size. After 1, 2, or 3 months' pretreatment with the same daily dose, followed by a 25-day drug-free period, no residual learning impairment was found. However, 6 months of daily administration of cannabis (tetrahydrocannabinol, 20 milligrams per kilogram) or alcohol (6 grams per kilogram) produced significant residual impairment of learning of maze and motor coordination tasks, 2 months or more after the last drug administration.

Metabolism of delta1-tetrahydrocannabinol by the isolated perfused dog lung. Comparison with in vitro liver metabolism

The metabolism of (-)-delta1-tetrahydrocannabinol (delta1-THC) has been studied in the isolated perfused dog lung. After intravascular administration of [3H]-delta1-THC there was an overall biotransformation of 12%. Two major metabolites were isolated and identified as 3'-hydroxy-delta1-THC and 4'-hydroxy-delta1-THC. 7-Hydroxy-delta1-THC was also present together with small amounts of 6alpha-hydroxy-delta1-THC and 6beta-hydroxy-delta1-THC. An in vitro experiment using a dog liver microsomal preparation was also carried out and showed that the major metabolites were 6beta-hydroxy-delta1-THC and 6alpha-hydroxy-delta1-THC. 7-Hydroxy-delta1-THC and 1,2-epoxy-hexahydrocannabinol were also isolated together with small amounts of 3'-hydroxy-delta1-THC and 4'-hydroxy-delta1-THC. The side-chain hydroxylated compounds are hitherto undescribed metabolites of delta1-THC.

Effects of various psychoative drugs on the metabolism of delta-tetrahydrocannabinol by rats in vitro and in vivo

Metabolism of 14C-tetrahydrocannabinol (14C-THC) by rat liver microsomal preparations in vitro was studied in the absence and presence of other psychoative drugs. Disappearance of 14C-THC, and changes in metabolite patterns as shown by thin layer chromatography, were studied. SKF 525-A, pentobarbital, phenobarbital and amphetamine all produced an apparently non-competitive inhibition of THC metabolism. The inhibition produced by meprobamate was at least partly competitive. Morphine and mescaline had no evident effect. SKF 525-A and the barbiturates markedly decreased the concentrations of all the major THC metabolites found in the incubation media. In contrast, none of the drugs tested in vivo, with the exception of SKF 525-A, had any effect on the biliary 14C-excretion or metabolite pattern, or on final tissue levels of 14C, when administered in doses comparable to those used for studies of interaction with THC in vivo. SKF 525-A, however, did markedly decrease the excretion of total 14C and alter the pattern of THC metabolities in the bile, and increased the final tissue 14C levels. It is concluded that in vivo interactions between THC and other psychoactive drugs are probably not explainable primarily on the basis of altered THC metabolism.