Study on the Specifications of Scutellariae Radix in Da-Chai-Hu-Tang Based on Efficacy in a Rat Model of Large Intestine Damp-Heat Syndrome and Chemical Composition Differences.

Scutellariae Radix comprises two specifications: Zi Qin (ZQ) and Ku Qin (KQ). Traditionally, ZQ preferentially clears large intestine heat, whereas KQ targets lung and stomach heat. Both function as ministerial components in Da-Chai-Hu-Tang (DCHT) for intestinal and inflammatory diseases, but pharmacological differences remain unclear. Using a rat model of large intestine damp-heat syndrome, this study compared the effects of ZQ, KQ, and their DCHT combinations (ZQ-DCHT, KQ-DCHT). Treatments significantly reduced body temperature, normalized thymus and spleen index (p < 0.05), and alleviated ileum and colon pathology. Levels of interleukin-1β, interleukin-2, interleukin-6, interleukin-10, and secretory immunoglobulin A were reduced significantly (p < 0.05), with ZQ/ZQ-DCHT exhibiting greater efficacy than KQ/KQ-DCHT at equivalent doses. This correlated with ZQ's higher baicalin (17.76% vs. 14.64%) and lower wogonin (0.21% vs. 0.35%) than KQ. Network pharmacology analysis suggested components might act through the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway. All treatments suppressed colonic phosphorylated STAT3 (p-STAT3) expression, with ZQ/ZQ-DCHT demonstrating higher inhibition than KQ/KQ-DCHT (excluding low-dose groups). These results indicated enhanced effects of ZQ/ZQ-DCHT in reducing immune-inflammatory markers. The efficacy might be attributed to baicalin, which modulated the colonic immune response by inhibiting p-STAT3 expression, leading to alleviation of inflammatory reactions.