Hydrangeae Dulcis Folium Attenuates Physical Stress by Supressing ACTH-Induced Cortisol in Zebrafish

Objective:To determine the effects of Hydrangeae Dulcis Folium(EHDF)on physical stress,changes in the whole-body cortisol level and behaviour in zebrafish(Danio rerio).Methods:One hundred and seventy-four fish were randomly divided into 4[adrenocorticotropin hormone(ACTH)challenge test:4 fish per group]or 6 groups(behavioural test:10–12 fish per group,whole-body cortisol:4 fish per group).Net handling stress(NHS)was used to induce physical stress.Fish were treated with vehicle or EHDF(5–20 mg/L)for 6 min before they were exposed to stress.And then,fish were sacrificed for collecting body fluid from whole-body or conducted behavioural tests,including novel tank test and open field test,and were evaluated to observe anxiety-like behaviours and locomotion.In addition,to elucidate the mode of action of the anti-stress effects of EHDF,ACTH(0.2 IU/g,i.p.)challenge test was performed.Results:The increased anxiety-like behaviours in novel tank test and open field test under stress were prevented by treatment with EHDF at 5–20 mg/L(P<0.05).Moreover,compared with the unstressed group,which was not treated with NHS,the whole-body cortisol level was significantly increased by treatment with NHS(P<0.05).Compared with the NHS-treated stressed control group,pre-treatment with EHDF at concentrations of 5–20 mg/L for 6 min significantly prevented the NHS-increased whole-body cortisol level(P<0.05).In addition,ACTH challenge test showed that EHDF completely blocked the effects of ACTH on cortisol secretion(P<0.05).Conclusion:EHDF may be a good antistress candidate and its mechanism of action may be related to its positive effects on cortisol release.