Background and purpose: Aloe vera is an anti-diabetic herb in traditional medicine. In the present study, the protective effect of aloe vera gel was studied on function of thyroid gland in diabetic rats.

Materials and methods: Fifty healthy male Wistar rats weighing 200-250g were randomized into 5 groups (n=10 per group). The animals in a control group were kept in normal conditions. In second group diabetes was induced by streptozotocin (STZ). In another group the streptozotocin induced diabetic rats received 400 mg/kg aloe vera gel once a day for 15 and 30 days. The next group included STZ-induced diabetic rats that received 10-15 units insulin once a day for 15 and 30 days. The Sham group included healthy normal rats that received 400 mg/kg aloe vera gel once a day for 15 and 30 days. By the end of days 15 and 30, the blood samples were taken. Then the animals were euthanized and the thyroid gland was removed and fixed in 10% buffered formalin. The semi-thin sections were prepared and stained using haematoxylin and eosin, and were observed under light microscope.

Results: Mean number and size of follicles significantly decreased in diabetic group compared to the control group (P<0.05). Histomorphometrical findings showed significant increase in mean number and size of follicles in the group receiving aloe vera gel compared to the diabetic group (P<0.05). There were significant decreases in concentrations of T3 and T4 hormones in diabetic group compared to those of the control group (P<0.05). Aloe vera treated animals showed significant increase in concentrations of T3 and T4 hormones compared to those of the control group (P<0.05).

Conclusion: Aloe vera gel could improve regeneration of damaged thyroid gland tissue in diabetic rats.