2.6. Acetic Acid-Induced Peritoneal Vascular Permeability Test

Mice were administrated in the same way as that in the xylene-induced ear edema test. The acetic acid-induced peritoneal vascular permeability test was carried out according to Zhang et al. with some modifications [13]. Briefly, 60 min after the final administration, mice were injected intravenously with 1% Evans blue solution (10 ml/kg) followed by an intraperitoneal injection of 0.6% acetic acid (0.1 ml/10 g). Twenty minutes after acetic acid injection, mice were sacrificed and the pigment that leaked into the abdominal cavity was rinsed two times with a total of 5 ml physiological saline solution. After that, the washing solution was centrifuged at 550 ×g for 15 min and the absorbance of the supernatant was measured at 590 nm with a Thermo Scientific Microplate Reader. To evaluate the inhibitory effect of PAO on the enhanced vascular permeability induced by xylene, the following equation was used:

where E_t is the average absorbance value of the treatment groups while E_v is the average absorbance value of the vehicle group.