Application of small animal ultrasound imaging technology for identification of polycystic ovary syndrome in a mouse model

Abstract

Background and aims: Polycystic ovary syndrome (PCOS) is a hormonal disorder common among women of reproductive age, characterized by irregular menstrual periods, elevated levels of androgens, and polycystic ovaries, leading to various symptoms and complications such as infertility, metabolic issues, and increased risk of diabetes and heart disease. This study aimed to compare traditional histological methods and ultrasound imaging for consistency in identifying PCOS in a mouse model. The shortest time to construct the PCOS model using letrozole was determined.

Methods: Female C57/BL mice were randomly divided into three groups: Group A received normal saline and a regular diet; Group B received 1 mg/kg/day of letrozole with a regular diet; and Group C received 1 mg/kg/day of letrozole with a high-fat diet. All mice were administered letrozole by intragastric gavage daily for five weeks. The traditional identification method included measuring body weight, examining vaginal smears, monitoring the estrous cycle, measuring serum androgen levels, and performing H&E staining of ovarian tissues. The PCOS model was evaluated using ultrasound imaging to identify and monitor follicles. The significance of the difference between the traditional identification method and the ultrasonic method was calculated using the nonparametric McNemar test, and consistency between the two methods was assessed with the kappa-coefficient test. On this basis, the ultrasound imaging technology was used to monitor the model-making process for 2, 3 and 4 weeks, and to monitor the parameters of the ovary and follicles to judge the shortest time that gavage letrozole caused the appearance of vesicular follicles in the mouse ovary.

Results: The traditional identification method showed no PCOS phenotype in group A mice, while groups B and C showed multiple ovarian cystic follicles, indicating successful model induction. The ultrasound imaging results were consistent with the traditional method, showing no PCOS in group A and multiple cystic follicles in groups B and C. The McNemar test revealed no significant difference between the traditional and ultrasonic identification methods. The kappa-coefficient test assessed consistency, yielding a value of 0.903, indicating strong agreement between the methods. The ovarian area, diameter, and the number and diameter of cystic follicles were not significantly changed at two weeks in the letrozole group compared with the control group. At three weeks, there were significant increases in the number and in the diameter of vesicular follicles compared with control cells. At four weeks, the number and diameter, the maximum cross-sectional area and diameter of the ovary were significantly increased compared with the control group.

Conclusions: The ultrasound and traditional methods provide consistent results for identifying PCOS in a mouse model. Construction of the PCOS model by letrozole gavage takes at least three weeks.

Keywords: High-fat diet; Letrozole; Model; Polycystic ovary syndrome; Ultrasonography.