Dual Regulating Effect of Shaoyao-Gangcao-Tang on COX-2 Expression in Acute and Resolution Phases of Carrageenin-Induced Pleurisy in Rats

Purpose: To investigate the effects and potential mechanisms of Shaoyao-Gangcao-Tang (SGT) on acute and resolution phases of carrageenin-induced pleurisy in rats. Methods: To determine the effects of SGT at 2 h, Sprague-Dawley rats received injection of 0.2 ml of 1 % λ-carrageenin into the pleural cavity after treatment with 4.0, 13.3 and 40.0 g/kg SGT for three days. At 2 h after pleurisy induction, exudate volume, total cell number, prostaglandin E2 (PGE2) production and cyclooxygenase-2 (COX-2) protein expression were measured. To determine the effects at 48 h, the rats were treated with SGT at 24, 36 and 46 h after injection of λ-carrageenin into the pleural cavity, and the exudate volume, total cell number, 15-deoxy-Δ^12, 14 -PGJ2 (15d-PGJ2) production and COX-2 protein expression were evaluated. Results: At 2 h after pleurisy induction, 13.3 and 40.0 g/kg SGT significantly decreased exudate volume by 34 (p 0.05) and b 4 0% (p 0.01), total cell number by 27 (p 0.05) and 41 % (p 0.01), PGE2 production by 17 (p 0.05) and 35 % (p 0.01), as well as COX-2 protein expression by 21 (p 0.01) and 43 % (p 0.01) compared with control group treated with saline. At 48 h after pleurisy induction, 13.3 and 40 g/kg SGT also significantly decreased exudate volume by 36 (p 0.05) and 55 % (p 0.01), as well as total cell number by 31 (p 0.05) and 43 % (p 0.01), but markedly increased 15d- PGJ2 production by 26 (p 0.05) and 51 % (p 0.01), as well as COX-2 protein expression by 50 (p 0.01) and 100 % (p 0.01) compared with control group. Conclusion: The findings suggest that SGT has dual regulating effect in acute and resolution phases of inflammation, involving inhibiting acute inflammation through down-regulation of pro-inflammatory mediators, and promoting inflammatory resolution through up-regulation of pro-resolution mediators.