The effect of maternal hypothyroidism on the postnatal development of the pituitary–thyroid axis in albino rats

Background
The adequate functioning of the maternal thyroid gland plays an important role in ensuring that the offspring develop normally. Therefore, maternal hypothyroidism and hyperthyroidism are associated with offspring abnormalities.
Aim of the work
This study was carried out to examine the effect of maternal hypothyroidism on the postnatal development of the pituitary–thyroid axis in the albino rat.
Materials and methods
Thirty pregnant female albino rats were divided into two groups. Group I was the control group and group II was the hypothyroid group whose rats were given carbimazole in a dose of 5 mg/rat/day through the intragastric intubation from the gestational day 10 until the postnatal day 20. The offspring of both groups were killed at the ages of newborn, 10, 30, and 60 days. The pituitary and thyroid glands were extracted from the pups of control and treated animals and processed for light and electron microscopy and morphometric analysis. In addition, an immunohistochemical study was carried out on the pituitary specimens for the detection of thyrotrophs.
Results
The present study revealed that the maternal hypothyroidism caused morphological changes in the pituitary–thyroid axis of the offspring. The changes started to appear in the newborn age and persisted throughout the postnatal life. The light microscopic examination revealed shrunken thyroid follicles. The follicular epithelial height increased and was composed of tall columnar cells with a vacuolated cytoplasm. The colloid decreased or was completely absent. Regarding the pituitary gland, there were many large pale vacuolated cells with dark nuclei and sometimes the vacuolation affected most of the cells. The electron microscopic examination of the thyroid follicular cells and thyrotrophs showed ultrastructural signs of an increased activity, which included dilated endoplasmic reticula, well-developed Golgi, enlarged mitochondria, and a decreased number of the secretory granules. Large cytoplasmic vacuoles were also observed. The immunohistochemical study of the pituitary gland revealed an increased number of thyroid-stimulating hormone immunopositive cells. The morphometric analysis of the pituitary and thyroid sections showed a significant decrease in the thyroid follicular diameter and a significant increase in the thyroid follicular epithelial height and in the number of the thyrotrophs per reference area.
Conclusion
From this study, it could be concluded that the experimentally induced maternal hypothyroidism disturbed the pituitary–thyroid axis of the offspring.