Effect of Hypophysectomy and Growth Hormone on the Light Cells of the Thyroid Gland

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Abstract
The influence of the hypophysis on the light cells of the thyroid gland—an epithelial cell type distinct from the follicular cell—was investigated by counting the number of these cells in hypophysectomized and in growth hormone-treated rats. Light cells were identified by a method consisting in injecting the rats with thyrotrophic hormone 90 minutes before they were sacrificed, thus inducing the formation of intracytoplasmic colloid droplets in the follicular cells, whereas the light cells contained none. In hypophysectomized rats, the light cells increased in number 2 to 4 times in the first 2 weeks after operation, and then did not change significantly up to 64 days. Unlike follicular cells, their size and general appearance were not different from those of intact rats, but they occurred more frequently in relatively large groups. Growth hormone injection in intact rats on alternate days induced a 2 to 3 times increase in the number of light cells during the first 8 days of treatment, and then this number did not change up to 64 days, whether or not the dose of growth hormone was increased progressively in the course of treatment. The diameter distribution of these cells was the same in growth hormone-treated as in control rats, and so was their general appearance. Growth hormone injected in hypophysectomized rats further increased the number of light cells, resulting in a number 8 to 9 times that of intact controls. These data indicate that the pituitary gland influences both follicular and light cells, but not in the same manner, since the hormonal factors involved are not the same. This work also confirms the view that a light cell is a cell type distinct from follicular cells.
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