This study was performed on 50 adult normal male albino rats. They were classified into 5 groups: The first group served as control. The sec ond, third and fourth groups were injected intraperitonealy with a daily dose (0.18 mg/200 g body weight) of diazepam for 10, 15 and 21 days respectively. The fifth group was injected with a daily dose (2 mg/200 g body weight) of midazolam for 10 days. Blood samples were taken from orbital sinuses and were subjected to biochemical assays for T3, T4 and TSH. Sepcimens from thyroid glands were taken for histological study using semithin sections.
The results of the study revealed that there is a transient effect of dia zepam and midazolam on the rats serum levels of thyroid hormones. This led to an increase in serum levels of thyroxine after 10 days of drug administration and reached its maximal level after 15 days and returned to its normal level by 21 days of diazepam therapy. On the other hand, TSH showing a significant decrease after 10 and 15 days and returned to its more or less normal levels by 21 days of the drug administration. Histological studies showed signs of thyroid activity represented by increase in: the number of thyroid follicles per field, cell height, nuclear size and vascularity of the gland.