Aim: The purpose of this study was to describe the morphologic alterations in somatotrophs, thyrotrophs and mammotrophs cells during evolution and regression of hypothyroidism.

Material and method: Eight rats were rendered hypothyroid by administration of 10mg/kg, intraperitoneally PTU (6-n-propyl-2-thiouracil). Four rats were sacrificed after 15 days of PTU administration. The other four rats were sacrificed on 15 days after interruption of PTU administration. Pituatary glands of anterior lobe was dissected and fixed in 2.5% glutaraldehyde in phosphate buffer. Semi-thin and ultrathin sections were determined by light and electron microscope.

Results: It was observed that numerous thyroidectomy cells with vacuolated cytoplasm in the adenohypophysis on the 15 days of PTU treatment rats. In the thyroidectomy cells the extreme dilation of the abundant RER and reduced of the secretory granules. Intracisternal granules the characteristic markers of thyroidectomy cells. Some somatotroph cells had a little dilated RER, but some of them had very large dilated RER structure and reduced of the secratory granules. Mammotroph cells generally similar to control group. It was observed that thyroidectomy cells reduced after 15 days interruption of PTU treatment. Some somatotrophs still had dilated RER.

Conclusion: In the experimental hypothyroidism, it was observed that number of thyroidectomy cells increased. Administration of PTU affected both somatotrophs and mammotrophs cells, but particulary somatotrophs. After interruption of drug adenohyphsis structure was showed similarity with control group.