2.7. Skin Nitrite Content

According to the instructions of the nitric oxide determination kit (Jiancheng, Nanjing, China), 300 μL of 10% homogenate supernatant was mixed with 200 μL of reagent one and 100 μL of reagent two. The mixture was mixed thoroughly, stood for 10 min, and centrifuged at 3500–4000 rpm for 15 min. The supernatant (160 μL) was added with 80 μL of the chromogenic agent, mixed well, and stood for 15 min. The OD values of each well were determined at 550 nm by a microplate reader (Gene, Hong Kong, China).