Functional variations in the ultrastructure of the thyroid gland in malnourished infant monkeys.

Healthy male pigtail monkeys (Macaca nemestrina) were procured at the age of 6-9 months, and fed either a 20 percent casein diet or a diet containing 2 percent casein as the sole source of protein. After 3-5 months, the malnourished monkeys developed many features usually associated with the clinical syndrome of marasmic kwashiorkor as seen in socioeconomically underpriviledged societies. Ultrastructural evaluation of thyroid gland revealed that dietary protein-calorie deficiency produced marked reduction in follicular cell height, conspicuous decrease in the number of apical filamentous microvilli, and a relative scarcity of the apical microvesicles as well as other pale staining colloid vesicles compared to findings on control glands. The electron-dense lysosomelike granules did not appear particularly affected, although in some sections they seemed to have increased in number and were located mainly in the basal portion of the cells, These electron-dense granules often displayed marked lack of homogeneity in regard to their structure in the malnourished glands. Most of these morphologic alterations have been noted frequently in thyroid glands of hypophysectomized animals, or in glands suppressed by the administration of thyroxine, and are therefore highly indicative of thyroid hypofuction in this animal prototype of human protein-calorie malnutrition.