Delta(9)-tetrahydrocannabinol and synthetic cannabinoids prevent emesis produced by the cannabinoid CB(1) receptor antagonist/inverse agonist SR 141716A.

There is substantial clinical evidence that Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and its synthetic analogs (nabilone and levonantradol) can prevent emesis in cancer patients receiving chemotherapy. Limited available animal studies also support the antiemetic potential of these cannabinoids. The present study investigates the mechanism of antiemetic action of cannabinoids in an established animal model of emesis, the least shew (Cryptotis parva). Since cannabinoid agonists prevent emesis, it was hypothesized that blockade of either the cannabinoid CB(1) receptor or the cannabinoid CB(2) receptor would induce vomiting. Thus, the emetic potential of SR 141716A (CB(1) receptor antagonist) or SR 144528 (CB(2) receptor antagonist) was investigated. Both intraperitoneal (0, 1, 2.5, 5, 10 and 20 mg/kg, n = 7-15 per group) and subcutaneous (0, 10, 20 and 40 mg/kg, n = 6-9 per group) administration of SR 141716A caused emesis (ED(50) = 5.52 +/- 1.23 and 20.2 +/- 1.02 mg/kg, respectively) in the least shrew in a dose-dependent manner. Indeed, both the frequency of emesis and the percentage of animals vomiting increased with increasing doses of SR 141716A. Significant effects were seen at the 10- and 20-mg/kg doses for the IP route, while only the 40-mg/kg dose produced significant emesis via the SC route. The CB(2) antagonist failed to produce emesis via either route of administration. SR 141716A at an IP dose of 20 mg/kg was used to induce emesis for drug interaction studies. Thus, varying doses of three different classes of cannabinoid agonists [CP 55, 940 (0, 0.1, 0.5 and 1 mg/kg), WIN 55, 212-2 (0, 1, 5 and 10 mg/kg), and Delta(9)-THC (0, 5, 10 and 20 mg/kg)], were administered IP to different groups of shrews 10 min prior to SR 141716A injection. The frequency of emesis was recorded for 30 min following the administration of SR 141716A. The order of potency for redcing both the frequency of emesis and the percentage of shrews vomiting was CP 55, 940 > WIN 55, 212-2 > Delta(9)-THC which is consistent with an action on the CB(1) receptor. These results suggest that the antiemetic activity of Delta(9)-THC and its synthetic analogs reside in their ability to stimulate the cannabinoid CB(1) receptor. Furthermore, the antiemetic potency of CP 55, 940 is 45 times greater than Delta(9)-THC. On the other hand, blockade of CB(1) receptors can induce vomiting, which implicates an important role for endogenous cannabinoids in emetic circuits.