Dynamics And Correlation Of Serum Cortisol And Corticosterone Under Different Physiological Or Stressful Conditions In Mice

As we all know, with the increasing pressure (stress) people faced, more and more studies about damage of body by stress are carrying out and the usual experimental animal are mice. Stress can cause changes of hormone in the serum of mice. Although plasma corticosterone is considered the main glucocorticoid involved in regulation of stress responses in mice, the presence of plasma cortisol and whether its level can be used as an indicatior for rodent activation of stress remain to be determined. In this study, effects of estrous cycle stage, circadian rhythm, and acute and chronic (repeated or unpredictable) stressors of various severities on dynamics and correlation of serum cortisol and corticosterone were examined in mice.Our results demonstrated that:(1) Cortisol contained in mouse serum because the reterntion time and molecular weight of plasma cortisol were consistent with the standard by HPLC and HPLC-MS.(2) A strong (r=0.6-0.85) correlation between serum cortisol and corticosterone was observed throughout the estrous cycle, all day long, and during acute or repeated restraints, chronic unpredictable stress and acute forced swimming or heat stress, but the response speed of two hormones to a variety of stressors is different.(3) No significant changes were observed in either cortisol or corticosterone concentration throughout the estrous cycle. However, contents of both hormones were higher at estrus than at other stages although the difference did not reach statistical significance.(4) Concentrations of both cortisol and corticosterone remained constant from 3:00 in the early morning to 15:00 in the afternoon, but they went up significantly at 20:00 in the evening.(5) Concentrations of both cortisol and corticosterone went up to the highest level on dav 1 of restraint. However, althoueh both hormones declined afterwards, the descent rate of corticosterone was faster than that of cortisol.(6) Concentrations of both cortisol and corticosterone are rising after restraint stress, forced swimming, heat stress (42 ℃) and shaker stress (160 rpm).(7) During both forced swimming and heat stresses, whereas the concentration of cortisol increased to the highest level within 3 min, the concentration of corticosterone did not reach the highest level until 40 min of the stresses. Results suggested that cortisol and corticosterone responded differently to severe stressors with cortisol being a quicker responder.(8) Both hormones went up to the highest level on day 1 of both repeated restraint and unpredictable stresses. After that, however, whereas the concentration of cortisol remained at the high level up to day 8 in both stress systems, the level of corticosterone showed different dynamics between repeated restraint and unpredictable stresses. Thus, wheras CORT declined dtamatically on each day of repeated restraints, it didn’t change significantly up to day 8 of the unpredictable stress. Results confirmed that the dynamics of CORT could be used as a better marker for animal adaptation to stress than could that of cortisol.In a word, results confirmed that the presence of cortisol in mouse serum and suggested that mouse serum cortisol and corticosterone were closely correlated in dynamics under different physiological or stressful conditions, but whereas corticosterone was a more adaptation-related biomarker than cortisol during chronic stress, cortisol was a quicker responder than corticosterone during severe acute stress. Therefore, the present results must be taken into account when choosing a biomarker for activation of different stresses.