Fine Structure of Pituitary Acidophils in Thyroidectomized Rats with or without the Treatment with Thyroxine and Dexamethasone

Electron microscopic study was made on rat anterior pituitaries in an attempt to clarify the causal mechanism of “loss of acidophils” which could be detected with the light microscope following thyroidectomy. In the advancing days after thyroidectomy, the acidophils (somatotrophs) were gradually deprived of their large granules whose diameter was about 350mμ. There was evidence in vivo for the first time that there were some acidophils containing only the small granules, about 130mμ in diameter, after the 7th postoperative day. This clearly showed the simultaneous existence of two different sizes of granules in the same acidophils. As time elapsed, the large granules dispersed from the acidophils. After the 30th day these acidophils began to adjust their shape into the polygonal cells. Eventually, the acidophils completely lacking granules of either size occassionally appeared on the 90th and 200th days. Thus thyroidectomy had a strong influence to release the large granules, whereas an influence to release the small ones was not remarkable. The replacement injection of thyroxine into the thyroidectomized rats efficaciously reproduced the large granules which were generally considered to be responsible for GH storage. The repeated administrations of dexamethasone to the thyroidectomized rats resulted in the increase in number of small granules that were thought by us to be the storage carriers of ACTH. On the other hand, this compound alleviated loss of large granules following thyroidectomy. The final fate of acidophils after thyro cectomy was, however, still vague because of the equivocal distinguishment of these degranulated acidophils from the immature basophils. Thus, the “loss of acidophils” may not mean the intrinsic disappearance of the cells themselves, but represent a transient loss of the large dense granules in the remaining acidophils.