Background Research on non-target organ damage of biological pesticides has attracted much attention. Rotenone exposure may be far beyond the occupational environment, and the exposureduring pregnancy may be increased through bioaccumulation, fruit or vegetable residues, and other forms of oral intake. At present, the effects of rotenone on placental development and its mechanism are still unknown.

Objective To investigate the developmental damage of rat placenta and evaluate the expression levels of glycogen synthase kinase (GSK-3β) and beta catenin (β-catenin) followed by rotenone exposure through the placental barrier during pregnancy, as well as to propose possible associated mechanisms.

Methods Eighteen sexually mature SD female infertile rats without specific pathogens were selected and divided into three groups: blank control group (0.9% saline), corn oil group, and rotenone group (corn oil + 2 mg·kg⁻¹ rotenone) by random number method, six female animals in each group. Another six male rats were selected and mated to the female rats at night with a female to male ratio of 3:1 per cage. Pregnant rats were given 0.9% saline, corn oil, and 2 mg·kg⁻¹ rotenone preparation by isovolumetric gavage once daily for the entire gestation period (19 d), and their conditions were observed after the last dose. The pregnant rats were anesthetized, and the size of the placenta and blood perfusion were detected by ultrasound the next day of the last dose of rotenone. Then, 3 pregnant rats in each group were sacrificed immediately and the placenta and umbilical cord tissues were dissected. The remaining 9 pregnant rats gave birth naturally, and the fetuses were observed for developmental evaluation and weighed. The histopathological changes of umbilical cord and placenta were observed by hematoxylin-eosin staining. The reactive oxygen species levels of placenta tissues were detected by flow cytometry. The Ca²⁺-ATPase activity of placenta tissues was detected by colorimetric method. The localization and levels of GSK-3β and β-catenin expression of placenta were detected by immunohistochemistry. The p-GSK-3β/GSK-3β and p-β-catenin/β-catenin protein expression in placental tissues were measured by Western blotting.

Results No injury or death was recorded during the pregnant rats receiving rotennon administration. Adverse pregnancy outcomes such as fetal absorption and postpartum stillbirth were found in the rotenone group, and the weight of the fetal mice decreased (P<0.05). The B-ultrasound showed disc-shaped placenta with a thick middle and thin edge, smooth fetal surface, rough maternal surface, visible placental lobules, granular echotexture of the placenta with comma-like echogenic densities, and chorionic plate showing deep indentations, no calcification, degeneration, or necrosis in each group. Compared with the corn oil group, the fetal surface diameter of the placenta was reduced in the rotenone group (P<0.05). The Doppler color ultrasound showed that interplacental blood flow was reduced in the rotenone group, while interplacental blood flow was abundant in the blank control and the corn oil groups. The hematoxylin-eosin staining results showed that smooth muscle cells in the umbilical cord tissues of rats were loosely arranged, with fuzzy nuclei and inflammatory infiltration in the rotenone group. The placental trophoblast cells were small in size, disorderly arranged with nuclear fragmentation and cytoplasm turbidity. The tissue reactive oxygen species level in the rotenone group was higher than those in the other two groups (P<0.05). The Ca²⁺-ATPase activity of placental tissues was reduced in the rotenone group (P<0.05). The immunofluorescence low-magnification observation showed that GSK-3β and β-catenin were expressed in placental tissue, weak fluorescence expression in the decidua basalis, strong fluorescence expression in the labyrinthine layer structure. The labyrinthine layer under high magnification showed that compared with the blank control group and the corn oil group, the brightness of β-catenin fluorescence expression in the rotenone group decreased (P<0.05), and the brightness of GSK-3β expression increased (P<0.05). The Western blotting results showed that the expression of β-catenin and p-GSK-3β proteins decreased (P<0.01), and the expression of GSK-3β protein increased (P<0.01) in the rotenone group. No significant expression of p-β-catenin protein was detected in the placenta tissue of each group.

Conclusion Rotenone exposure during pregnancy induces placental hypoperfusion, growth retardation, and oxidative stress in rats, as well as down-regulation of β-catenin and p-GSK-3β protein expression, and up-regulation of GSK-3β protein expression, which may further lead to abnormal pregnancy and fetal restricted growth.