Tolerance to the effect of delta1-tetrahydrocannabinol on corticosterone levels in mouse plasma produced by repeated administration of cannabis extract or delta1-tetrahydrocannabinol

1 Three injections of cannabis extract (500 mg/kg s.c. given over 3 or 5 days) diminished thymus gland weight but not the weights of spleen or liver in weanling female and adult male mice kept at room temperature.2 Both cannabis extract (500 mg/kg s.c.) and Delta(1)-tetrahydrocannabinol (Delta(1)-THC; 10 and 20 mg/kg i.p.) elevated corticosterone levels in mouse plasma.3 A pretreatment that consisted of three daily subcutaneous injections of 500 mg/kg of cannabis extract and that was shown to produce tolerance to the ;cataleptic' effect of Delta(1)-THC (2 mg/kg i.v.) in mice, also produced tolerance to the effect of Delta(1)-THC (10 mg/kg i.p.) on corticosterone levels in mouse plasma. However, this pretreatment did not reduce the rise in plasma corticosterone concentration produced by immobilization.4 Tolerance to the effect of Delta(1)-THC (10 mg/kg i.p.) on corticosterone levels in mouse plasma was also produced by the pretreatment of mice with a single injection of Delta(1)-THC (10 mg/kg s.c.). Three daily injections of Delta(1)-THC (10 or 30 mg/kg s.c.) also produced tolerance.5 In a thermoneutral environment (30-32 degrees C) in which cannabis extract does not produce hypothermia, the drug no longer reduced thymus gland weight. However the effect of cannabis extract and of Delta(1)-THC on corticosterone plasma levels was the same at room temperature as at 30-32 degrees C. Tolerance to the latter effect of Delta(1)-THC was also produced equally readily under the two conditions.6 It is concluded that pretreatment with cannabis extract or Delta(1)-THC can produce tolerance to the effect of Delta(1)-THC on corticosterone levels in mouse plasma and does so without impairing the effect of immobilization stress on corticosterone release. In addition, both the rise in corticosterone plasma levels produced by cannabis or Delta(1)-THC and the development of tolerance to this effect can still take place in the absence of hypothermia.

Brain levels of delta1-tetrahydrocannabinol and its metabolites in mice tolerant to the hypothermic effect of delta1-tetrahydrocannabinol

Repeated voluntary consumption of cannabis in milk (approximately 8 mg per day for 15 days) produced in mice tolerance to the hypothermic effect of tritiated Delta(1)-tetrahydrocannabinol ([(3)H]-Delta(1)-THC; 2 mg/kg i.v.) but not to the effect of [(3)H]-Delta(1)-THC on immobility index. The development of tolerance was not accompanied by any detectable change in levels of radioactivity in the brain assigned to Delta(1)-THC or its metabolites. It was concluded that changes in metabolism or distribution of Delta(1)-THC are not responsible for tolerance at least to the hypothermic effect of Delta(1)-THC in mice.

The ring test: a quantitative method for assessing the 'cataleptic' effect of cannabis in mice

1. A bioassay for cannabis, called the ring test, has been developed in which the percentage of the total time spent on a horizontal wire ring during which a mouse remains completely immobile is recorded.2. The effect of cannabis on mobility is a dose-related, graded response.3. Threshold doses of cannabis extract are 12.5 mg/kg when injected intravenously, and 100 mg/kg when injected intraperitoneally or subcutaneously.4. The method provides a measure of the ;cataleptic' effect of cannabis. Chlorpromazine in doses of 1 mg/kg upwards also produces the effect but barbitone does not.5. It is concluded that Delta(1)-tetrahydrocannabinol (Delta(1)-THC) is largely responsible for the effect of cannabis extract on mobility; the potency ratio of Delta(1)-THC to cannabis extract is between 10 and 20. Delta(1)-Tetrahydrocannabidivarol (Delta(1)-THD) also affects mobility but is less active than Delta(1)-THC. Cannabidiol has no effect when injected intraperitoneally in doses up to 100 mg/kg.

A metabolic interaction in vivo between cannabidiol and 1 -tetrahydrocannabinol

The effect of pretreatment with cannabidiol (CBD; 50 mg/kg i.p.) on the distribution of radioactivity in chromatograms of ethyl acetate extracts of the brains of mice injected with tritiated Delta(1)-tetrahydrocannabinol ((3)H-Delta(1)-THC; 1.0 mg/kg i.v.) was determined. The pretreatment with CBD produced significant increases in the levels of radioactivity in the brain assigned to Delta(1)-THC and its centrally active metabolite 7-hydroxy-Delta(1)-THC: the changes produced were respectively 1.4 and 2.0 fold.Pretreatment with CBD did not bring about any detectable change in the degree of 'catalepsy' produced by Delta(1)-THC. This negative finding may have been due to the wide limits of error that were obtained in the bioassay.

Effect of cannabis and certain of its constituents on pentobarbitone sleeping time and phenazone metabolism

1. Cannabis extract prolonged sleeping time in mice in a thermally neutral environment (30-32 degrees C) in which hypothermia does not occur. The prolongation was dose related, just detectable at 50 mg/kg, and 4-fold at 500 mg/kg.2. Under these conditions, ether sleeping time was not prolonged.3. Cannabis extract inhibited the aerobic metabolism of phenazone by a microsome-rich 9,000 g supernatant of mouse liver homogenate capable of nicotinamide adenine dinucleotide phosphate (NADPH) generation.4. Delta(1)-Tetrahydrocannabinol (Delta(1)-THC) prolonged pentobarbitone sleep and inhibited phenazone metabolism, but its action was limited, and could not account for the effect of the extract. The carotenes and water-soluble fractions of the extract were inactive on pentobarbitone sleep.5. Cannabidiol was strongly active by both tests; in vivo 39.8 muM/kg (12.5 mg/kg) prolonged sleep by 190%, and in vitro 12.7 muM inhibited phenazone metabolism 20%. These actions were dose related, and could account for the effect of the extract.6. The prolongation of pentobarbitone sleep by cannabis extract in a dose of 200 mg/kg, intraperitoneally, was maximal when given 30 min before the pentobarbitone, still present at 3 h, but undetectable at 24 hours. No phase of enhanced metabolism at 24 or 48 h after single cannabis injection was detected.7. It is concluded that cannabis extract inhibits microsomal activity of mouse liver, chiefly by virtue of its cannabidiol content. It is probable that cannabis consumption by man could lead to altered disposal of many other drugs, used in medicine or otherwise.