Effects Of Controlled Ovarian Hyperstimulation On Thyroid Structure And Function In Mice And Its Secondary Effects On The Uterus

Since the world’s first test-tube baby was born in 1978,Assisted Reproductive Technology(ART)has been more and more widely used.Controlled ovarian hyperstimulation(COH)is a routine procedure of assisted reproductive technology.It promotes the development of multiple follicles through the use of exogenous gonadotropins,thereby obtaining more eggs to increase the pregnancy rate.However,the use of exogenous gonadotropins leads to abnormal elevation of estradiol(E2)levels in the body,which may cause disorders in the hypothalamic-pituitary secretion system.The thyroid gland is an organ located on the hypothalamic-pituitary axis,so the secretion of thyroid hormones may be affected by E2.The uterus as the environment for gestation of the fetus,in addition to being directly affected by E2,may also be affected secondary to changes in thyroid function after COH.Previous studies on the effects of COH on the thyroid gland were mostly investigative studies on clinical cases.Therefore,the impact of COH on the structure and function of the thyroid gland was evaluated.Whether this effect was dose-dependent and whether the environment that further affected the embryonic development still had problems Significance.In this study,three groups of mice models were constructed using 8-week-old ICR female mice:low-dose ovulation induction group(2.5IU),high-dose ovulation group(5IU)and natural ovulation cage Group(spontaneous ovulation,SO),in which the SO group was used as a control group.The three test time points from the conception to the third trimester were E0.5,E7.5 and E17.5.The effects of COH on the thyroid structure and function and its secondary effects on the uterus in mice were investigated by measuring serum hormone levels,thyroid morphological analysis,thyroid function-related gene detection,uterine morphological analysis,and oxidative stress markers at these three time points.The results showed that the trend of each index of the SO group from E0.5 to E17.5 accorded with the normal pregnancy mother.Compared to the SO group,at each time point from E0.5 to E17.5,the 2.5 IU group was tested for hormone levels:serum E2,thyroid-stimulating hormone(TSH),and free triiodothyronine(fT3).There was no significant difference in the level of free thyroxine(fT4).Under the light microscope,quantitative analysis of the thyroid follicular tissue structure revealed no significant differences in the follicle epithelium height,colloid area,and colloid/follicular area ratio.The thyroid follicular epithelial cells were observed by transmission electron microscopy and found no obvious abnormality at E0.5.The mitochondrial crest was disappear at E7.5 and E17.5.Real-time PCR was used to detect the expression of key genes Tshr,Tpo,Tg,Nis,Pax8 and Titfl in thyroid hormone synthesis pathway.It was found that at E7.5,the relative expression of Pax8 was significantly reduced(P<0.05).There were no significant differences at all time points.Uterine oxidative stress indicators MDA and SOD were detected and it was found that MDA content was significantly increased at E7.5,and there was no significant difference in SOD at each time point.Under light microscope,E0.5 endometrium and E7.5 decidua tissue were observed,and there was no significant difference with SO group.The immunohistochemical results of the GB1 gamma-aminobutyric acid(GABA)receptor showed that GB1 was expressed in the intimal granulosa cells of the stroma and the expression level in the 2.5 IU group was smaller than that in the SO group.Compared with the SO group,serum E2 levels in the 5IU group were significantly higher than those in the SO group at E0.5 and E7.5(P<0.05);there was no significant difference in TSH levels at each time point;fT3,fT4 The level was significantly decreased at E0.5 and E7.5(P<0.05).At E17.5,there was no significant difference between E2,fT3,and fT4 compared to SO.Under light microscopy,the follicle tissue structure was quantitatively analyzed.It was found that at E7.5,the height of follicle epithelium was significantly lower(P<0.05),the colloid area was significantly increased(P<0.05),and the colloid/follicular area ratio was significantly increased.(P<0.05).The thyroid follicular epithelial cells were observed under transmission electron microscope and it was found that in the 5 IU group,the top vesicles were less at E0.5;at the E7.5,the top vesicles were significantly reduced;At E17.5,the endoplasmic reticulum and the top vesicles did not change significantly.In addition,ambiguous mitochondria were observed at each time point.The expression of the key genes Tshr,Tpo,Tg,Nis,Pax8 and Titfl in the thyroid hormone synthesis pathway was detected and the relative expression of Tshr in the 5 IU group at E0.5 was significantly reduced(P<0.05);at E7.5,The relative expression of Tshr and Pax8 was significantly decreased(P<0.05);the relative expression of Pax8 was still significantly decreased at E17.5(P<0.05).Uterine oxidative stress indicators MDA and SOD were detected and it was found that MDA content was significantly increased at E7.5,and there was no significant difference in SOD at each time point.Under light microscope,the endometrium of E0.5 and uterine decidua of E7.5 were observed.It was found that at E0.5,the uterine glands were more curved than the SO group,and there was no obvious abnormality in the decidua tissue at E7.5.Immunohistochemical results of GB1 showed that there was no strong positive signal on the intimal granulosa cells of E0.5 and E7.5.In terms of thyroid structure and function indicators,and indicators related to uterine oxidative stress,the adverse effects of high-dose propulsion group were higher than low-dose group.In summary,COH has a negative effect on the structure and function of the thyroid gland in mice,which in turn may have adverse secondary effects on the uterus,and this negative effect of controlled superovulation has a certain dose Dependency.