Physiological behaviour of cultured porcine thyrocytes according to ultrastructure, iodide uptake and protease activity detected by synthetic substrate (red). a: Porcine thyrocytes form follicles with formation of apical microvilli and intercellular tight junctions when stimulated with 1.3 mU/ml TSH for 30h. b: Upon stimulation with TSH, iodide uptake of thyrocytes is increased 6.8 times compared to unstimulated cells (mean ± SEM is shown). TSH-induced iodide uptake is inhibited by 1 mM perchlorate and significantly reduced upon exposure to TSH + 2 mM thiamazole (p < 0.05). c: Upon stimulation with TSH for 30h, DPP II activity is seen in all cells, whereas activity of APN at the plasma membrane in seen only in thyrocytes integrated in follicles but not in isolated cells (d, arrowhead). N: nucleus, FL: follicular lumen.