Histochemical Studies of Thyroid Cells in Long-Term Tissue Culture1

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Abstract
Histochemical techniques were applied to lamb thyroid cells maintained in longterm tissue culture (190 days) and also subjected to thyrotropin (TSH) stimulation. The results of nonstimulated and TSH-stimulated cells were compared in order to establish whether longterm tissue culture and TSH stimulation alter enzymatic patterns as related to the process of secretion. The findings indicate that in non-stimulated cultures aging had no significant effect on organelles except for acid phosphatase-rich granules (lysosomes), which showed increased activity with age. Acid phosphatase, DPNHnitro BT reductase, thiamine pyrophosphatase and the exogenous horse-radish peroxidase used as markers for lysosomes, endoplasmic reticulum, the Golgi apparatus and the pinocytotic vacuoles, respectively, were found to respond to TSH-stimulation in young follicular cells in culture. The age-activity relationship of acid phosphatase and intracytoplasmic PAS-stained droplets suggested that in tissue culture acid phosphatase-rich granules may be involved in the digestion of accumulated PAS-stained droplets. Histochemical evidence indicates that trypsin-dissociated cells of the lamb thyroid gland possess in culture under conditions of stimulation morphologic characteristics suggestive of secretion. Morphologic transformations attributed to conditions in culture were evident after the 20th or the 30th day. Enzymatic reactions applied to TSH-stimulated aged cells did not reveal significant alterations in organelles. This is interpreted as a diminished responsiveness of aged cells to TSH stimulation and is considered as a sign of loss of specialized function.