The cannabinoid agonist WIN55,212-2 suppresses opioid-induced emesis in ferrets.

BACKGROUND: Cannabinoid receptor agonists reverse nausea and vomiting produced by chemotherapy and radiation therapy in animals and humans but have not been tested against opioid-induced emesis. This study tests the hypothesis that cannabinoid receptor agonists will prevent opioid-induced vomiting. METHODS: Twelve male ferrets were used. They weighed 1.2-1.6 kg at the beginning and 1.8-2.3 kg at the end of the experiments. All drugs were injected subcutaneously. WIN55,212-2, a mixed CB1-CB2 cannabinoid receptor agonist, was administered 25 min before morphine. Retches and vomits were counted at 5-min intervals for 30 min after morphine injection. RESULTS: Retching and vomiting responses increased with increasing morphine doses up to 1.0 mg/kg, above which the responses decreased. Previous administration of naloxone prevented morphine-induced retching and vomiting. WIN55,212-2 dose-dependently reduced retching and vomiting. The ED50 was 0.05 mg/kg for retches and 0.03 mg/kg for vomits. At 0.13 mg/kg, retching decreased by 76% and vomiting by 92%. AM251, a CB1 receptor-selective antagonist, blocked the antiemetic actions of WIN55,212-2, but AM630, a CB2 receptor-selective antagonist, did not. CONCLUSIONS: These results demonstrate that WIN55,212-2 prevents opioid-induced vomiting and suggest that the antiemetic activity of WIN55,212-2 occurs at CB1 receptors. This is consistent with findings that CB1 receptors are the predominant cannabinoid receptors in the central nervous system and that antiemetic effects of cannabinoids appear to be centrally mediated.

Allodynia and hyperalgesia produced by specific inhibition of spinal c-fos expression: lack of correlation with dynorphin content.

Inhibition of spinal Fos expression increases formalin-induced nociception and decreases spinal prodynorphin messenger ribonucleic acid (mRNA), suggesting that Fos modulates nociception by inducing dynorphin synthesis. This study tests the hypothesis that Fos modulates sensitivity to other somatic stimuli, such that inhibition of Fos expression will result in tactile allodynia and thermal hyperalgesia. In addition, it correlates the somatosensory effects of inhibition of Fos expression with spinal dynorphin content. Antisense oligodeoxynucleotide (ODN) to c-fos mRNA was administered by intrathecal infusion. Tactile sensitivity was tested by probing the hindpaw with von Frey filaments. Thermal sensitivity was quantitated by using withdrawal latency to radiant heat. Two percent formalin was injected into the dorsal hindpaw, and flinches were quantitated. Fos was quantitated by counting immunoreactive cells. Dynorphin was measured by immunoassay. Intrathecal antisense, but not mismatch, ODN resulted in tactile allodynia, thermal hyperalgesia, and hyperalgesia to formalin-induced nociception. Antisense ODN decreased Fos-like immunoreactivity after formalin injection but did not alter Jun-like immunoreactivity. Antisense ODN had differing effects on spinal dynorphin content, depending on the method of administration. These experiments show a role of Fos in modulating somatosensory sensitivity and suggest that induction of dynorphin synthesis is not the sole mechanism by which Fos does so.

The interactive toxicity of CHCl3 and BrCCl3 in precision-cut rat liver slices.

The interactive toxicity of two nontoxic concentrations of chloroform (CHCl3) and bromotrichloromethane (BrCCl3) was examined in precision-cut rat liver slices. Liver slices were prepared from male Sprague-Dawley rats (220-250 g) pretreated with phenobarbital for 4 days. Toxicants were administered 1 hr apart. Intracellular K+ levels were similar to untreated controls in slices treated with 0.2 mM CHCl3 or 0.125 microliters (0.25 mg, 1.26 mumol) BrCCl3 alone, indicating that these concentrations were nontoxic. However, addition of both toxicants, irrespective of order, resulted in a time-dependent loss of intracellular K+ which was significant at 9 hr following administration. This was interpreted as evidence of synergistic toxicity. Cytochrome P450 loss was significant as early as 3 hr following exposure to BrCCl3, alone or when added with CHCl3. This loss may be attributed to BrCCl3-induced suicide inactivation of cytochrome P450. Centrilobular hepatocytes may be more susceptible to the interactive toxicity of CHCl3 and BrCCl3. Activity of enzymes found predominantly in this area was significantly decreased in slices exposed to both toxicants relative to controls. Conversely, activity of enzymes found predominantly in the periportal region was similar to that of untreated and treated controls. Interactive toxicity of BrCCl3 and CHCl3 was not a consequence of increased lipid peroxidation or depletion of slice glutathione content. Further studies need to be conducted to elucidate the mechanisms mediating the interactive toxicity of BrCCl3 and CHCl3.

Further examination of the selective toxicity of CCl4 in rat liver slices.

Lipid peroxidation and loss of enzymes located predominantly in either periportal or centrilobular hepatocytes were investigated in precision-cut liver slices from male Sprague-Dawley rats. Pretreatment of animals with 80 mg/kg phenobarbital for the site-specific enzyme studies enhanced and accelerated CCl4 toxicity in slices resulting from increased radical formation. Liver slices were exposed to 0.57 mM CCl4 by vaporization using a roller incubation system at 37 degrees C for a total of 9 hr. Conjugated diene formation, an index of lipid peroxidation, was detected 15 min following CCl4 administration and increased over time. Loss of cytochrome P450 occurred in a time-dependent manner relative to controls where levels in treated slices were 42% of controls at 9 hr. A 48-hr fast prior to termination increased intracellular K+ leakage relative to that present in slices from fed animals. Significant leakage of glucose-6-phosphate dehydrogenase and beta-glucuronidase from centrilobular hepatocytes occurred 9 hr following CCl4 administration. The content of the periportal enzymes (lactate dehydrogenase and sorbitol dehydrogenase) was unchanged in the same slices over the duration of the experiment. Reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide, a mitochondrial selective dye and indicator of viability, was significantly lower in treated slices from phenobarbital-treated animals at 9 hr relative to controls. These studies demonstrate that precision-cut slices are an ideal in vitro system for mechanistic studies and the investigation of site-specific toxicants since the integral architecture of the liver and cellular identity are maintained.

The hepatotoxicity of chloroform in precision-cut rat liver slices.

Chloroform hepatotoxicity was investigated in precision-cut liver slices from male Sprague-Dawley rats pretreated with phenobarbital to predispose animals to CHCl3 intoxication. Liver slices were exposed to 0.2, 0.5 and 1.0 mM chloroform for a total of 9 h in a roller culture system. Intracellular K+ loss was found to be concentration- and time-dependent over the duration of the experiment. Histopathological changes were also evident. Glucose 6-phosphate dehydrogenase and beta-glucuronidase were significantly decreased at 3 h relative to controls where a loss of 61% and 36% occurred, respectively. Enzyme levels of alanine aminotransferase and lactate dehydrogenase, both found predominantly in periportal hepatocytes, remained identical to controls over the duration of the experiment. A significant time-dependent depletion of glutathione occurred as early as 3 h following the administration of 0.5 mM chloroform. Mitochondrial viability, measured by the reduction of a specific dye, was significantly lower than controls in treated slices at 6 h following chloroform administration. Precision-cut liver slices appear to be especially useful for the biochemical and histopathological examination of site-specific hepatotoxicants such as CHCl3.