ObjectiveTo explore the mechanism by which Xiaoyaosan regulates HPT axis dysfunction in the rat model with the syndrome of liver depression and spleen deficiency by observing its effect on the glycoprotein hormone α-subunit （CGA）/glutathione peroxidase 2 （GPX2）/thyroid-stimulating hormone β-subunit （TSHβ） pathway for thyroid hormone synthesis. MethodsSeventy-two male SD rats were randomized into six groups： normal， model， high-dose （16.7 g·kg^-1）， medium-dose （8.35 g·kg^-1）， and low-dose （4.175 g·kg^-1） Xiaoyaosan， and fluoxetine （0.001 8 g·kg^-1） groups， with 12 rats in each group. The rat model of liver depression and spleen deficiency was induced by chronic restraint stress for 21 days. The intervention groups were treated with Xiaoyaosan decoctions or fluoxetine suspension， respectively. After modeling， hematoxylin-eosin staining was employed to observe morphological changes in the thyroid and pituitary tissue of the rats. Serum levels of triiodothyronine （T3）， tetraiodothyronine （T4）， and thyroid-stimulating hormone （TSH） were measured by enzyme-linked immunosorbent assay （ELISA）. Real-time fluorescence quantitative polymerase chain reaction （Real-time PCR） and Western blot were employed to determine the mRNA and protein levels， respectively， of TSH receptor （TSHR） in the thyroid tissue， thyrotropin-releasing hormone receptor （TRHR） and TSHβ in the pituitary tissue， and thyrotropin-releasing hormone （TRH）， CGA， GPX2， and TSHβ in the hypothalamic tissue. ResultsCompared with the normal group， the model group showed significant atrophy and irregularity of thyroid follicles， a marked reduction in colloid secretion， extensive vacuolar degeneration of adenocytes in the anterior pituitary， lowered serum levels of T3， T4， and TSH （P<0.01）， and down-regulated mRNA and protein levels of TSHR in the thyroid tissue， TRHR and TSHβ in the pituitary tissue， and TRH， CGA， GPX2， and TSHβ in the hypothalamic tissue （P<0.01）. Compared with the model group， high- and medium-dose Xiaoyaosan and fluoxetine alleviated the pathological changes in the thyroid and pituitary tissue， outperforming the low-dose Xiaoyaosan group. Moreover， they elevated the serum levels of T3， T4， and TSH （P<0.05， P<0.01）. The serum TSH level was also elevated in the low-dose Xiaoyaosan group （P<0.05）. The mRNA and protein levels of TSHR in the thyroid， TRHR and TSHβ in the pituitary， and TRH， CGA， GPX2， and TSHβ in the hypothalamus were up-regulated in the high- and medium-dose Xiaoyaosan groups （P<0.05， P<0.01）. Additionally， the mRNA and protein levels of TSHβ in the hypothalamus were up-regulated in the low-dose Xiaoyaosan group （P<0.01）. In the fluoxetine group， the mRNA and protein levels of TSHR in the thyroid， TRHR in the pituitary， and TRH， CGA， and GPX2 in the hypothalamus were up-regulated （P<0.05， P<0.01）. ConclusionThe downregulation of CGA/GPX2/TSHβ pathway may be one of the biological mechanisms underlying HPT axis dysfunction in the rat model with the syndrome of liver depression and spleen deficiency. Xiaoyaosan may regulate the HPT axis dysfunction by up-regulating the CGA/GPX2/TSHβ pathway.