Elevated Insulin-Like Growth Factor-1-Induced Female Rats Perpetuate the Polycystic Ovary Syndrome Phenotype: Pathological Mechanism of Insulin-Like Growth Factor-1 in Polycystic Ovary Syndrome

Abstract

Objectives: This study was designated to establish a polycystic ovary syndrome (PCOS) rat model with recombinant human insulin-like growth factor-1 (RH-IGF-1). We made assessment on the characteristics of hyperinsulinemia and hyperandrogenism in the rat model. Design: This study performed the characteristics of PCOS upon RH-IGF-1 injection and evaluated the disease process of PCOS syndrome caused by the insulin-resistant pathological condition of IGF-1 based on the comparative study of in vivo test. Setting: The experiment was conducted in the experimental research center of Yinzhou NO.2 hospital, Ningbo, Zhejiang Province, China. Materials and Methods: Thirty-four female Sprague Dawley immature rats aged 21 days were randomly divided into two groups. Those treated with RH-IGF-1 2 mg/100 g daily were in RH-IGF-1 group (n = 20), and those with 0.9% sodium chloride 0.2 mL/100 g daily were in the saline group (n = 14). The experiment was carried out in two stages. In stage I, rats were anesthetized upon the first estrous cycle in the saline group with tissue and blood samples collected (n = 7), and rats in the RH-IGF-1-treated group were anesthetized on the 5th day after vaginal opening (VO) (n = 10). In stage II, rats in the saline group were anesthetized after three complete cycles (n = 7), meanwhile, while on the 15th day after VO (n = 10) for those in the RH-IGF-1 group. Results: We have found that compared with the control group, rats injected with RH-IGF-1 expressed an early VO, disordered estrous cycle, polycystic ovaries, and significantly increased ovarian weight/body weight ratio. And from the perspective of hormone secretion, their androgen increased significantly and the insulin resistance index also elevated distinctly, possessing main characteristics similar to PCOS. Limitations: In this study, we were limited by the inability to examine IGF-1 in hypothalamus. IGF-1 in hypothalamus and in vitro experiments would be taken into consideration for further study in the future. Conclusions: These findings suggest that IGF-1 may be a key factor in the pathogenesis of PCOS, and the increase of androgen may be the pathological result, not the cause of PCOS.