Objective: To observe the effect of Shuyu capsule on μ-opioid receptors (MOR) expression in the hypothalamus of premenstrual syndrome (PMS) with liver-qi stagnation model rats

and to investigate its possible mechanism. Method: Rats were selected by using an open field test and vaginal smear in this experiment. The selected rats were divided into 4 groups:the normal group

the model group

the Shuyu capsule group(0.408 g·kg-1) and the naloxone group(0.4 mg·kg-1). The PMS with liver-qi stagnation model in rats was prepared by a chronic bondage stress method. The distribution and protein level of MOR in hypothalamus of rats were observed by immunofluorescence chemical technology and Western blot. Result: Compared with the normal group

the scores of open field test decreased

the distribution of messy-arranged MOR in hypothalamus increased

MOR protein expression increased in the model group (P<0.01). Compared with the model group

the scores of open field test increased

the distribution of messy-arranged MOR in hypothalamus decreased

MOR protein expression decreased in the Shuyu capsule and naloxone groups (P<0.01). Conclusion: Shuyu capsule could improve the symptoms of PMS with liver-qi depression syndrome

which may be achieved by regulating the MOR in the hypothalamus. In addition

the up-regulation of MOR in the central nervous system may be one of the pathophysiologic mechanisms.