Insulin improves ovarian function during the ovarian cycle in adult mice

Folliculogenesis is controlled by numerous inside and outside ovarian factors such as endocrine, paracrine, and autocrine signals. Among these factors, insulin is an important molecule that regulates processes in the female reproductive system. So, the purpose of this study was to determine the impact of insulin treatment on ovary tissue during the ovarian cycle. For this probe, 18 adult female NMRI mice were randomly divided into two groups: control and insulin (100 µL with a 72-hour interval by intraperitoneal injection for 30 days). Blood samples for hormonal evaluation were obtained from the heart, and the serum levels of FSH, LH, progesterone, and estradiol were measured. Then, right and left ovaries were extracted for real-time PCR and stereology, respectively. According to our results, insulin administration increased mRNA levels of INS-R, Ki67, while reduced Caspase-3, IGF-1, and FOXO-1. Insulin administration augmented the concentrations of female reproductive hormones. Histological analyses showed that the total volume of ovary in mice receiving insulin was significantly reduced. Likewise, a significant decrease in the number of antral follicles, Graafian follicles, and the number of corpora lutea were seen following the use of insulin. In contrast, the results showed a significant growth in the number of primordial and primary follicles in the insulin group compared with the control group. Briefly, insulin administration is able to increase the expression of genes related to insulin receptor and cell proliferation, as well as the amount of female reproductive hormones, but simultaneously, has a dual effect on the histological parameters of the ovary.