Changes in expression of steroidogenic acute regulatory protein (StAR) gene in lithium-treated rats during luteinization

Background: The rate limiting step in progesterone synthesis by corpus luteum appears to be the movement of cholesterol from the outer to the inner mitochondrial membrane that is facilitated by a novel protein named steroidogenic acute regulatory (StAR) protein. Recently we have found a reduction in StAR protein expression following lithium chloride (LiCl) treatment in gonadotropin-stimulated rat. In the present study, the effect of lithium on the expression of StAR gene and serum levels of progesterone were investigated. Methods: Immature 23 days old Wistar rats were induced with injection of pregnant mare's serum gonadotrophin (PMSG) followed by injection of human chorionic gonadotropin (hCG). Then, rats were injected with either LiCl or saline at 12 hours post- hCG injection. Ovaries were collected at 4-hour interval from 8 to 24 hour post- hCG injection. Expression of StAR gene was determined by semi quantitative RT-PCR. In addition, serum levels of progesterone were measured by ELISA. Results: Our results showed that in response to the gonadortopin treatment, serum levels of progesterone increased in both control and LiCl-treated animals, but it significantly decreased in LiCl-treated animals as compared with the control. Also significant decreases were observed in expression of StAR gene in early stage of luteinization following LiCl treatment. Conclusion: It is concluded that LiCl is an effective suppressor of StAR expression, and also the critical step of the progesterone synthesis was affected by LiCl treatment in gonadotropin-stimulated rat.