Electron microscopic observations on the thyroid gland of two species of teleost, Semicossyphus reticulatus and Sebastiscus marmoratus. (a part of phylogenetic studies of the fine structure of the thyroid)

Effect of thyroid-stimulating hormone on the physiology and morphology of the thyroid gland in coho salmon,Oncorhynchus kisutch

Activity of the thyroid gland of the coho salmon,Oncorhynchus kisutch, was assessed by physiological, histological and ultrastructural criteria after treatment with graded doses of bovine thyrotropin (bTSH) in January and March. Average plasma thyroxine (T4) levels increased from about 0.8 ng/ml in saline-injected controls to about 15 ng/ml in fish treated with four intraperitoneal injections of 0.8 lU bTSH. Light-microscope observations of one μm-thick sections stained with methylene blue and azure II, showed that bTSH treatment increased epithelial height in both presmolts and smolts. Ultrastructural manifestations of increased activity owing to bTSH treatment were also seen, along with evidence of follicle proliferation. Cytoplasmic organelles and secretory granules increased in numbers with increased dosage of bTSH.

Ultrastructural changes in the parrotfish thyroid afterin vitro stimulation with bovine thyrotropin

Six groups of thyroid glands ofScarus dubius were examined and compared by electron microscopy after anin vitro culture for 4h with graded doses of bovine thyrotropin (bTSH). Five doses of bTSH were used encompassing the full range of the dose-response curve developed for this tissue. Upon electron microscopic examination, micrographs were taken randomly and at the same magnification, and three intracellular inclusions were quantified. The relative surface density of rough endoplasmic reticulum (rER) and the relative surface area of lysosomes and engulfed colloid droplets were recorded for each group. Three treatment groups, (1) control, no bTSH, (2) tissues exposed to 1 mIU/ml bTSH, and (3) tissues exposed to 2 mIU/ml bTSH, did not differ from each other in the quantified organelles nor in general appearance. Overall, these three groups were similar in appearance to the ultrastructure described in other teleosts except for a lack of flagellated cells. Compared to the first three groups, treatment with 5 mIU/ml bTSH, increased the density of rER, and the proportion of cell area occupied by lysosomes and engulfed colloid. This group also possessed either more microvilli or pseudopods at the lumenal surface of the follicular epithelium. After exposure to 10 mIU/ml bTSH there was an even greater increase in surface density of rER, and in surface area occupied by lysosomes and engulfed colloid droplets. The apical portion of this group was highly irregular, commonly displaying pseudopods. Group (6), (20 mIU/ml), showed a decline in cytoplasm in comparison to group (5) with many epithelial cells breaking apart. A few cells in this group were still intact but contained huge engulfed colloid droplets which extended from the basal to apical borders. This first detailed description suggests that the teleost thyroid gland undergoes ultrastructural changes with exogenous TSH stimulation in a manner similar to that seen in higher vertebrates.