Abstract: Soy isoflavone （SIF） had effect on decreasing blood lipids. The present research focused on whether it could lose body weight by regulating leptin level. The experiment was designed to investigate the effects of SIF on leptindependent signaling in hypothalamus of obese rats. Foodinduced obese rats model was established by feeding with high oil diet， then the obese rats were randomly divided into four groups （GroupⅠⅣ） fed with SIF 0 （control group）， 50 （low dose group）， 150 （medium dose group） and 450 （high dose group） mg·kg–1 body weight， respectively. In addition， the control group （Group V, basis group） rats were fed with low oil basal diet. The experiment lasted for 4 weeks. At the end of the experiment， all experimental rats were euthanized with pentobarbital sodium and sections of their hypothalamus were prepared and stained with HE. The expressions and positive rates of the main proteins of leptinJAK/STAT signaling, i.e. OBRb， JAK2， pSTAT3， SOCS3， NPY were detected by immunohistochemical SABC， respectively. The results showed that the expressions and positive rates of OBRb， JAK2， pSTAT3 in high dose SIF group and basis group were both significantly higher than those in other groups （P＜0.05）， and their expression levels were raising with the increased dose of SIF. On the contrary， the levels and positive rates of SOCS3 and NPY in high and basis group were the least compared with other groups， and the difference was significant （P＜0.05）， but the expression of NPY was rising in dorsomedial nucleus and paraventricular nucleus following the increased dose of SIF. Above all， SIF had affect on leptindependent signaling road. In conclusion， the five proteins were closely related to body energy regulation. SIF could lose body weight by interfering the leptinJAK/STAT signaling of hypothalamus in obese rat in a dose dependent manner.

Key words: soy isoflavones, immunohistochemical SABC, OBRb, JAK2, pSTAT3, SOCS3, NPY