持续光照对雌性大鼠青春期启动的影响

Effect of continuous light on the puberty initiation in female rat

目的观察持续光照对雌性大鼠青春期启动的影响。方法 40只21日龄离乳大鼠,随机分为持续光照组和对照组。持续光照组给予24 h持续光照,对照组给予12 h/12 h昼夜循环光照。1周后检测大鼠血清雌二醇(E2)、促黄体生成素(LH)、促卵泡生成素(FSH)、泌乳素(PRL)、睾酮(T)、褪黑素(MT)水平,其中MT采取多时点取材的方法,包括暗期和光期各3个时间点。随后观察大鼠阴门开启日及第1次出现动情间期的时间;40日龄时所有大鼠行旷场试验进行行为学评估;继续饲养至45日龄,各组处死6只大鼠并取松果体行形态学检查。结果持续光照组大鼠的血清E2、LH、FSH、PRL、T水平均明显高于对照组,差异有统计学意义(P<0.05)。暗期各时点对照组的褪黑素水平均高于持续光照组,差异有统计学意义(P<0.05),光期各时点两组间的差异无统计学意义(P>0.05)。持续光照组阴门开启日龄及第1次动情间期出现时间均早于对照组,差异均有统计学意义(P<0.05)。行为学评估发现,与对照组相比,持续光照组大鼠处于焦虑烦躁的状态。大鼠松果体HE染色显示,持续光照组松果体细胞明显减少,排列松散欠规则,对照组松果体细胞细胞数较多,排列紧致规则;电镜下,持续光照组胞核皱缩,呈现凋亡样改变,超显微结构多方面异常,对照组未见明显异常。结论过度光照可抑制大鼠褪黑素分泌,具有性腺促进作用,可导致性发育提前。

Objective To investigate the effect of continuous light on the puberty initiation in female rats. MethodsForty 21-day-old female rats were weaned and randomly divided into two groups, continuous light group and control group. Continuous light group were exposed to light 24 hours a day while control group were exposed to 12h：12h light：dark cycle. After one week, E2, LH, FSH, PRL, T and MT were measured. MT was measured at different time points including zeitgber time（ZT） 2, ZT6, ZT10, ZT14, ZT18 and ZT22. The age at vaginal opening and first diestrus were observed. Behavior evaluation was carried out when rats were 40 days old. Rats were sacrificed at the age of 45 day and pineal gland was observed morphologically. Results The levels of E2, LH, FSH, PRL and T were significantly higher in continuous light group than in control group（P〈0.05）. MT level in control group during dark time was significantly higher than that in continuous light group（P〈0.05）. No significant difference was observed in MT level during daytime（P〈0.05）. The age at vaginal opening and first diestrus were earlier in continuous light group than control group（P〈0.05）. Open field test showed that the rats in continuous light group were more anxious than in control group. HE staining of pineal gland showed decreased and loosely distributed pineal cells in continuous light group. TEM test found that the nuclei in continuous light group had apoptosis-like changes and other ultrastructural changes. Conclusions Excessive light can inhibit the secretion of melatonin and enhance the activity of sexual gland, which can result in the earlier sexual development.