Vitamin D 3 Activates Phosphatidylinositol-3-Kinase/Protein Kinase B via Insulin-Like Growth Factor-1 to Improve Testicular Function in Diabetic Rats.

Objective. In diabetes mellitus, vitamin D-3 deficiency affects sex hormone levels and male fertility; however, the mechanism leading to the disorder is unclear. This research was designed to investigate the mechanism of vitamin D-3 deficiency and hypogonadism in diabetic rats. Our aim was to assess serum vitamin D-3 levels and the relationship among vitamin D-3, insulin-like growth factor-1 (IGF-1), and testicular function. Materials and Methods. Rats with streptozotocin-induced diabetes were randomly divided into four groups and treated with different doses of vitamin D-3: no vitamin D-3, low (0.025 g/kg/day), high (0.1 g/kg/day), and high (0.1 g/kg/day) with JB-1 (the insulin-like growth factor-1 receptor inhibitor group, 100 g/kg/day). The groups were compared with wild-type rats, which function as the control group. Various parameters such as vitamin D-3 and IGF-1 were compared between the experimental and wild-type groups, and their correlations were determined. Results. Twelve weeks of vitamin D-3 supplementation improved the testosterone levels, as shown by the increase in the level of serum IGF-1 in diabetic rats. Phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT), which was a downstream of the signaling pathway of IGF-1, was significantly increased after vitamin D-3 treatment. Conclusions. The study shows that vitamin D-3 may promote the expression of testosterone and improve testicular function in diabetic rats by activating PI3K/AKT via IGF-1.