The ultrastructural study of oocyte and zona pellucida in ovarian follicles of untreated and and metformin-treated diabetic rats subsequent to induction of experimental diabetes

Diabetes is a metabolic disorder affecting the whole body systems including the female reproductive organs. Moreover, diabetes is an important cause of infertility. Metformin is commonly used to control hyperglycemia in patients with diabetes. This study was done to evaluate the ultrastructural changes of ovarian follicles in diabetic rats and their response to metformin. Thirty-six adult Sprague-Dawley female rats (170-210 g) were studied in three groups (Control, diabetic and metformin-treated rats). In the second and third groups, diabetes was induced by injection of streptozotocin (45 mg/kg). The rats in the third group were later treated by metformin monohydrochloride (100 mg/kg). At the end of the experiment, rats were sacrificed and their right ovaries were observed under transmission electron microscope. Quantitative data were analyzed by student t-test in SAS software. In comparison with the control group, significant decreases in zona pellucida thickness and the mean number of microvilli were observed (respectively, P<0.01 and P<0.001) in diabetic rats. Significant decreases in zona pellucida thickness were also observed in metformin-treated rats (P<0.05) but changes in the number of microvilli were non-significant. The number of organelles in oocyte cytoplasm was higher and they were natural or natural-looking in metformin-treated rats versus the diabetic ones. Reduction in the number of mitochondria and their ballooning cristae were of the most noticeable changes in diabetic rats. Diabetes decreases the number of microvilli and oocyte organelles and diminishes zona pellucida thickness leading to structural changes in the organelles but metformin could improve the aforesaid conditions.