Intraperitoneal injection of lipopolysaccharide (LPS) was used to elicit a sublethal, shock-like condition in mice. LPS, 2.5 mg/kg i.p., induced hypothermia, elevated serum TNF-alpha levels and lethality over a 48 h period in male CD-1 mice. The 5-lipoxygenase (LO) inhibitors, WY-50,295 tromethamine and zileuton (100 mg/kg p.o), significantly inhibited hypothermia at 4, 24 and 48 h after LPS. Interestingly, whereas cyclooxygenase (CO) inhibitors (ibuprofen, etodolac, naproxen and tenidap) at 40-80 mg/kg p.o. stimulated hypothermia at 4 h, they significantly reduced the later stages of hypothermia at 24-48 h. Rolipram (PDE-IV inhibitor) and dexamethasone significantly reduced hypothermia at 4-24 h and 1-24 h, respectively. All the anti-inflammatory agents significantly reduced elevated TNF-alpha levels at approximately 70 min post-LPS, except for ibuprofen. In conclusion, these anti-inflammatory standards indicate that LPS-induced shock involves multiple lipid mediators (PG's, LT's and possibly PAF) and secondary cytokine generation. This sublethal model of LPS-induced shock represents a sensitive model for estimating the efficacy of potential drug candidates for the treatment of endotoxic shock.
Pretreatment with captopril, a kininase II inhibitor, at 10 mg/kg i.p. or s.c., significantly increased the writhing response induced by a minimum effective dose (0.75 mg/kg i.p.) of phenylbenzoquinone (PBQ), by 91-148%. 1,10-Phenanthroline, a carboxypeptidase B inhibitor (2 mg/kg i.p.), in combination with captopril enhanced the algesic effect of PBQ by 309-360%. Captopril also doubled the number of writhes induced by a minimum effective dose of BK (5 micrograms/kg i.p.) in PGE2-pretreated mice. The writhing responses induced by higher doses of PBQ or BK were not affected by these inhibitors. The hyperalgesic effect of BK (1 micrograms) injected into the hindpaw of rats was significantly increased and prolonged by coinjection of captopril (30 micrograms) and 1,10-phenanthroline (30 micrograms) and was prevented by carboxypeptidase B (1 mg). These data indicate that BK plays a role in pain in these models, a role which appears of greatest relevance at threshold algesic stimulation.
The intraperitoneal injection of 1 mg/kg PGE2 (which by itself was inactive) enhanced the writhing response induced by a subnociceptive dose of bradykinin (BK, 0.5 mg/kg ip) in male mice. The BK1 agonist, DesArg9-BK and the BK1 antagonist DesArg9-Leu8-BK did not affect writhing. The BK2 agonists, Lys-BK and Tyr-BK, like BK, induced writhing in the PGE2-treated mice. On the other hand, the DPhe7-analogs of BK, which antagonize BK at the BK2 subtype of receptors, potently inhibited the writhing response induced by BK. The writhing was also inhibited by morphine, but in contrast, non-steroidal antiinflammatory drugs (NSAIDs) only weakly inhibited the writhing response in this assay, suggesting that the nociceptive effect of BK was not significantly dependent upon the biosynthesis of PGE2. These results suggest that the algesic effect of BK in this mouse model is mediated via a BK2 receptor subtype.
PEM-420, the active isomer of pemedolac, inhibited the writhing responses induced by phenylbenzoquinone (PBQ), acetic acid, and acetylcholine in mice with ED50's of 0.80, 0.92, and 0.075 mg/kg p.o., respectively. In the rat acetic acid writhing assay, PEM-420 exhibited an ED50 value of 8.4 mg/kg p.o. In the Randall-Selitto test, PEM-420 raised the pain threshold of the yeast-injected paw (ED50 = 0.55 mg/kg p.o.). Like other NSAIDs, PEM-420 inhibited the PBQ-induced production of PGI2 and PGE2 in the mouse peritoneal cavity, with ED50 values of 0.5 and 1.2 mg/kg p.o., respectively. It had weak ulcerogenic liability in rats (acute UD50 = 99 mg/kg p.o. in fasted rats; subacute UD50 = 74 mg/kg/day for 4 days in fed rats). The data indicate that PEM-420 is a potent and safe peripheral analgesic.
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