Pituitary ACTH and GH Content Associated with the Loss of Acidophils Following Thyroidectomy

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Functional significance of the remarkable loss of the rat pituitary acidophils following thyroidectomy was investigated upon histological observation along with the measurement of pituitary trophic hormones. Following thyroidectomy, the pituitary GH content was lowered, and the acidophils decreased in number and pnally was not perceptible after the 15th postoperative day. But pituitary ACTH was kept within the normal range. Administration of dexamethasone (DM), 0.2mg/100g/day, for 15 or 30 days to the normal rats raised not only the number of acidophils but also the pituitary ACTH content. DM did not, however, induce any change in pituitary GH content. When the thyroidectomized rats were given the same dose of DM for 15 days from the 15th postoperative day, the population of acidophils and pituitary GH content in those rats showed a moderate restoration and ACTH content increased signipcantly.
These results indicate that the loss of the acidophils following thyroidectomy may merely depend upon the depletion of their α-granules, and may not mean the genuine disappearance. The loss of acidophils is, therefore, likely to be a simulative phenomenon. The present evidence upon the histometrical estimation and measurements of hormones is favourable to the reconprmation of our previous view that the large granules in the acidophils are responsible for GH and the small ones for ACTH storage. The mechanism of the loss of GH granules following thyroidectomy was discussed in this paper.