Background: Diabetes mellitus (DM) and osteoporosis are two frequent medical conditions with an increasing prevalence in elderly people and are responsible for large number of incurable fractures. This study is designed experimentally in female rats in order to determine whether combined treatment of insulin and parathyroid hormone (PTH) enhances the reversibility of the osteoporotic changes that occurred in streptozotocin (STZ)-induced DM.

Materials and methods: In this study, 30 adult female rats aged 3 months were used, they were randomly divided into: control group (6 rats) and diabetes group (24 rats), in which experimental DM was induced by i.p. injection of a single dose of STZ (60 mg/kg/body weight). Diabetic group was further divided into four subgroups (6 rats each): non-treated diabetic, insulin-treated (8–12 units s.c./day of Humalin U-40), PTH-treated (6.0 μg s.c./kg/day) and combined insulin and PTH-treated subgroups. All tested groups were assessed for body weight, food and water consumptions.

Results: At the end of the experimental period, the bone mineral density (BMD) was measured for all rats of different groups; then the rats were sacrificed and blood samples were collected for measuring glucose, alkaline phosphatase and osteocalcin levels. Right femora were dissected out and subjected to measurement of diameter of neck and shaft, length of shaft, and weight. Then the femora specimens were processed and stained with haematoxylin and eosin for histological study. The results showed that there was a statistically significant, decrease in BMD, increase in the level of alkaline phosphate, and decrease in the level of osteocalcin in rats in diabetic group compared with other groups; these parameters improved in other groups, especially in diabetes/insulin/PTH group. The rats in diabetic group showed statistically significant decrease in neck and shaft diameters and weight of femur bone compared with other groups, while rats in diabetes/insulin/PTH group showed a significant improvement of these parameters. In diabetic group, there were different histopathological changes in cortical bone and Haversian canals, which improved in other groups, especially in rats in diabetes/insulin/PTH group.

Conclusions: The untreated DM resulted in dramatic reduction in BMD and morphometric parameters. Treatment with insulin ameliorated these effects to some extent, while PTH co­-treatment had a more positive effect. The combination of PTH and insulin resulted in stronger improvement of all parameters to approximately like those of control rats.