Elucidating dosage-effect relationship of different efficacy of rhubarb in constipation model rats by factor analysis

Rhei Radix et Rhizoma (rhubarb), as the preferred representative of cathartic drugs of traditional Chinese medicine (TCM), has a long history of medicinal use and multifarious functions that produce a wide range of dosage. In modern times, rhubarb and its prescriptions are not only used to treat common clinical diseases, but also achieve good results in the treatment of acute, dangerous, severe and difficult diseases. However, rhubarb also has an alias called "General", which means that its efficacy is relatively rapid.

The present study was conducted to simultaneously elucidate dosage-effect relationship of rhubarb of different efficacy, "Removing accumulation with purgation" (E1) and "Clearing heat and purging fire" (E2), providing reference for the safe and effective usage of rhubarb.

Three-week-old rats were randomly divided into the normal control group (Con.), model group (Mod.) and rhubarb groups with six doses (0.135, 0.27, 0.81, 1.35, 4.05, 8.1 g/kg). We established a constipation model with gastrointestinal accumulated heat induced by dyspepsia, taking defecation characteristics observed by metabolic cages, alvine pushing rate, gastrointestinal hormones in serum, etc., as indicators of E1, and taking TG, Na⁺-K⁺-ATPase, inflammatory factors and proteins, etc., as indicators of E2. The factor analytic approach was used to systematically evaluate the two effects and analyze the corresponding dosage-effect relationship.

The levels of Gas, AchE, TG, Na⁺-K⁺-ATPase, TNF-α, IL-1β, (p-)NF-κB p65, (p-)p38, (p-)ERK and p-JNK in model rats increased significantly while the levels of defecation, fecal water content, MTL, SS, ET, NTS, VIP, JNK and TLR4 decreased. Compared with the Mod., in rhubarb groups, the increase of faeces, alvine pushing rate, most gastrointestinal hormones, etc., reflected the therapeutic efficacy of E1, and the reduction of TG, Na⁺-K⁺-ATPase, expression levels of inflammatory indexes, etc., reflected the impact of E2. After the analysis, the effective threshold dose ranging from 0.67 to 5.37 g/kg (corresponding to 7.44-59.67 g in the clinic) was in the EC₂₀-EC₈₀ range for E1 treatment and from 0.78 to 5.60 g/kg (equivalently clinical 8.67-62.22 g) was for E2 treatment. And the 1.6- and 1.2-fold rhubarb highest dose of Chinese Pharmacopoeia might be the optimal doses for E1 and E2 respectively. In general, however, the concentration of rhubarb liquid for overall efficacy is suggested to be between middle and highest dose of Chinese Pharmacopoeia.

A constipation model was used to elucidate two main effects of rhubarb, which was consistent with the characteristics of TCM syndrome. In the wide range of rhubarb dosage, low doses might have little or no effect and although high concentrations of rhubarb liquid enhanced curative efficacy, it would also have certain side effects on the body. Therefore, scientific-based experiments and rational analysis by mathematical models could contribute to the safe and effective application of rhubarb in the clinic.