Adverse effects of 4-tert-octylphenol on the production of oxytocin and hCG in pregnant rats

Abstract

Endocrine-disrupting chemicals (EDCs) are exogenous substances that alter the structure or function of the endocrine system. 4-Tert-octylphenol (OP) is one of the most representative EDCs and has estrogenic effects. In this study, we examined the effects of ethinyl estradiol (EE) and OP on the pituitary gland, placenta, and uterus of pregnant rats. Expression levels of human chorionic gonadotropin (hCG), oxytocin (OT), and contraction-associated proteins (CAPs) were determined, and uterine contractile activity was measured by uterine contraction assay. EE and OP both increased mRNA expression of OT and hCG in the pituitary gland but not the placenta. Since OT and hCG control uterine contraction, we next examined CAP expression in the uterus. Expression of 15-hydroxyprostaglandin-dehydrogenase (PGDH) was upregulated by OP, whereas expression of other CAPs was unaffected. To clarify the effect of OP on uterine contraction in pregnant rats, uterine contraction assay was performed. The 17β-Estradiol (E2) did not affect contraction of primary uterine cells harvested from pregnant rats in a 3D collagen gel model. However, OP showed different effects from E2 by significantly reducing contraction activity. In summary, we demonstrated that OP interferes with regulation of OT and hCG in the pituitary gland as well as PGDH in the uterus, thereby reducing uterine contraction activity. This result differs from the action of endogenous E2. Collectively, these findings suggest that exposure to EDCs such as OP during pregnancycan reduce uterine contractile ability, which may result in contraction-associated adverse effects such as metratonia, bradytocia, and uterine leiomyomata.

Keywords: 4-tert-octylphenol; Endocrine-disrupting chemicals; endocrine factors; estradiol; pregnant rats.

Figure 1

Transcriptional regulation of hCG and OT by EE and OP in the pituitary gland.Transcription levels of OT, α-hCG, and β-hCG were analyzed by Q-PCR. Data were expressed as the mean±SD of at least six rats per group. Gene expression level was normalized to that of an internal control gene (1A). ^*P<0.05 compared to control group.

Figure 2

Transcriptional regulation of hCG and OT by EE and OP in the placenta. Transcription levels of OT, α-hCG, and β-hCG were analyzed by Q-PCR. Data were expressed as the mean±SD of at least six rats per group. Gene expression level was normalized to that of an internal control gene (1A). ^*P<0.05 compared to control group.

Figure 3

Transcriptional regulation of CAPs by EE and OP in the uterus. Transcription levels of OT, OTR, PGDH, and FP were analyzed by Q-PCR. Data were expressed as the mean±SD of at least six rats per group. Gene expression level was normalized to that of an internal control gene (β-actin). ^*P<0.05 compared to control group.

Figure 4

Uterine contraction differentially modulated by E2 and OP. Primary uterine cells from pregnant rats were mixed with a collagen solution and seeded in 12-well plates for 3D contraction assay. Collagen lattices were treated with E2 (10^-7 M) and OP (10^-7 M) for the indicated time periods. Images were captured and analyzed to measure contractile activity. 10% FBS were used as positive controls while unstimulated lattices were used as a negative control. ^*P<0.05 compared to control group at 24 h and ^#P<0.05 compared to control group at 48 h.