To study blood capillary growth in the hyperplastic thyroid gland, rats were fed 0.25% thiouracil in a low iodine diet for time intervals up to 100 days. Thyroids were fixed by vascular perfusion and embeded in Epon. Whole lobes were sectioned from pole to pole and slides were prepared of sections every 0.3 mm. Capillaries were clearly enlarged by 3 days and they enlarged progressively thereafter. By 3 days, the cells of many neighboring capillaries came into close apposition and from this time on, there was evidence of fusion of capillary walls in the form of partial septa in the capillary lumens. Fusion continued until 20 days, when follicles were almost completely surrounded by a continuous endothelial sheet and unfused capillary walls were separated by connective tissue. The vascular pattern around peripheral follicles changed in a way similar to interior follicles, except that in places, capillaries were gradually excluded from the space between epithelium and thyroid capsule. Vascular enlargement was restricted to the thyroid blood vessels. There was no obvious enlargement of the blood capillaries of the parathyroid despite its close proximity to the thyroid.

We have prepared thyroid follicles in suspension culture to use as a model system in vitro for investigation of some properties of the thyroid gland. The follicles were free of endothelial cells, fibroblasts, and other nonepithelial cells. They were prepared by collagenase treatment of minced rat thyroid glands followed by differential filtration of the suspension through nylon meshes. Small clusters of principal thyroid epithelial cells were separated from large fragments and single cells. They were cultured in dilute suspension in Coon's modified F-12 medium in dishes coated with agarose to avoid having the cells attach to the dishes. By culture day 3, most of the clusters formed closed follicles containing a periodic acidSchiff-positive colloid but without a basal lamina. Follicle walls contained an occasional C cell. The epithelium resembled that in the thyroid of a recently hypophysectomized rat, with normal polarity and organelle complement normal with respect to position and abundance, with basally located lysosomes, no pseudopods, and no colloid droplets. The cells were responsive to thyroid-stimulating hormone (thyrotropin) and to dibutyryl cyclic AMP. Thyroid-stimulating hormone at 10 munits/ml resulted in apical migration of lysosomes and formation of pseudo ods and colloid droplets within 30 min; Ionger exposure resulted in depletion of luminal colloid. The results indicate that the suspended follicles resemble follicles in vivo with respect to morphology and responsiveness to thyroid-stimulating hormone in the absence of other cell types. There have been many studies of the properties of thyroid cells in monolayer cultures (1-4). These studies were generally of mixed cultures of various cell types. Many characteristic functional properties of the thyroid could be demonstrated in some of these preparations but only for a limited.time (5-7). However, the shape of the epithelial cells, their organelle complement, and the relationship of the cells to each other show profound differences from the thyroid in vivo and such preparations cannot be considered as adequate thyroid models.It would be useful to have as a model system in vitro a preparation consisting of the principal thyroid epithelial cells alone and organized in follicles. Using methods that have some similarities to those introduced by Mauchamp (8), we have succeeded in preparing a suspension of thyroid epithelial cells free of fibroblasts and endothelial cells and arranged as follicles with lumens. In this paper we describe the method of preparation of these follicles and some of their morphologic properties.MATERIALS AND METHODS Dissociation. Thyroids were excised from 5-to 6-week-old Fischer rats killed by asphyxiation with CO2. The glands were freed from surrounding nonthyroid tissues, minced, and washed in Hanks' calcium-and magnesium-free salt solution. The tissue was then placed in tissue culture dishes, at 370C for 3 hr, in the complete tissue culture medium (described below) containing 1 mg of collagenase (Worthington, CLS II...

Shortly after the administration of 1~0 unit thyrotropin to rats, 24 hours post-hypophysectomy, the following sequence of changes has been observed within thyroid follicular epithelial cells: (1) the appearance of apical cell surface activity consisting of pseudopods projecting into the follicular lumen; (2) apparent phagocytic engulfment of colloid droplets lacking indications of acid phosphatase activity; (3) close association and probable fusion of newly formed colloid droplets and dense granules, the latter cytochemically positive for acid phosphatase activity; (4) the appearance of presumptive acid phosphatase activity within colloid droplets; and, (5) further colloid droplet changes, viz., basipetal migration and decrease in size, accompanied by an increase in density and in demonstrable acid phosphatase activity. These changes appeared to represent the resorption and degradation of follicular colloid. Comparable results were obtained using intact and more heavily stimulated animals. Colloid biosynthesis was tentatively visualized in these cells as a separate mechanism involving small vesicles prominent in the Golgi region and beneath the apical plasma membrane of some, but not all, thyroid follicular cells in each specimen.