Acute effects of thyroid-stimulating hormone on cultured thyroid cell morphology

The acute effect of TSH on the ultrastructure of dog thyroid cells in monolayer tissue culture was examined by scanning electron microscopy. Although thyroid cells in monolayer culture remained responsive to TSH stimulation, the cell surface changes induced by TSH were different from those seen in intact thyroid tissue. Morphological changes were observed within 15 min after the addition of TSH, the earliest time point examined. These changes were fully developed within 4 h. Spontaneous morphological transformation was not observed in the absence of TSH. Morphological alterations induced by TSH were 1) the thickening and retraction of the cell border, 2) the formation of a network of cytoplasmic projections resulting from both cell retraction and active cytoplasmic extension, and 3) an increase in the number of surface microvilli. The relationship between this acute TSH action and thyroid hormone synthesis and secretion remains to be clarified.