Total flavonoids extracted from xiaobuxin-tang on the hyperactivity of hypothalamic-pituitary-adrenal axis in chronically stressed rats

Abstract

Our previous studies have demonstrated that the total flavonoids (XBXT-2) isolated from the extract of Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, ameliorated behavioral alterations and hippocampal dysfunctions in chronically stressed rats. Studies over the last decades have suggested that the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis is one of the most consistent findings in stress-related depression. Herein, we used the same chronic mild stress model of rats as before to further investigate the effect of XBXT-2 on the hyperactivity of HPA axis, including the stress hormones levels and glucocorticoid receptors (GRs) expression. Our ELISA results showed that chronic administration of XBXT-2 (25, 50 mg kg(-1), p.o., 28 days, the effective doses for behavioral responses) significantly decreased serum corticosterone level and its upstream stress hormone adrenocorticotropic hormone (ACTH) level in chronically stressed rats. Furthermore, western blotting result demonstrated XBXT-2 treatment ameliorated stress-induced decrease of GRs expression in hippocampus, an important target involved in the hyperactivity of HPA axis. These results were similar to that of classic antidepressant imipramine treatment (10 mg kg(-1), p.o.). In conclusion, the modulation of HPA axis produced by XBXT-2, including the inhibition of stress hormones levels and up-regulation of hippocampal GRs expression, may be an important mechanism underlying its antidepressant-like effect in chronically stressed rats.

Figure 1

An outline of the design for the experiment (top: with time course for CMS and post-CMS tests; bottom: CMS protocol).

Figure 2

Effect of XBXT-2 on the serum corticosterone level in chronically stressed rats. Serum corticosterone concentration was detected using a commercial ELISA kit. Each column represents as the mean ± SEM, n = 8. **P < .01 compared with control-vehicle; ^## P < .01 compared with stress-vehicle (ANOVA followed by Newmann-Kuels tests).

Figure 3

Effect of XBXT-2 on the serum ACTH level in chronically stressed rats. Serum ACTH concentration was detected using a commercial ELISA kit. Each column represents as the mean ± SEM, n = 8. ***P < .001 compared with control-vehicle; ^### P < .001 compared with stress-vehicle (ANOVA followed by Newmann-Kuels tests).

Figure 4

Effect of XBXT-2 on hippocampal GRs expression in chronically stressed rats. The intensity of western bands was quantified with a densitometric scanner. Each column represents as the mean ± SEM, n = 5. Band 1: control + vehicle; Band 2: stress + vehicle; Band 3: stress + IMI (10 mg/kg, p.o.); Band 4: stress + XBXT-2 (25 mg/kg, p.o.); Band 5: stress + XBXT-2 (50 mg/kg, p.o.); ***P < .001 compared with control-vehicle, ^## P < .01 compared with stress-vehicle (ANOVA followed by Newmann-Kuels tests).

Figure 5

Main molecular targets of XBXT-2 that underlie its antidepressant-like effect. Arrows indicate down-regulation or up-regulation. CRF, corticotropin-releasing factor; ACTH, adrenocorticotropic hormone; GC, glucocorticoids; GR, glucocorticoid receptors.