ABSTRACT
Thyroid gland is composed of follicles surrounded by basement membrane, which is known to be related to the regenerative processes in several organs. This study was performed to observe the morphological details and changes of the basement membrane components, which are the presumtive factors in thyroid regeneration, with time sequences after partial thyroidectomy and then the relations between the components and thyroid regeneration were confirmed. Thyroid galnds of adult male rats were examined before and 1, 2, 3, 4, 5, 7 and 10 days after bilateral partial[50-60%] thyroidectomy. The basememnt membranes of follicles were prominent with high eosinophilicity at later stage when H & E stained. But in PAS and EM staining, the basement membrane of the operated groups didn`t show any specific changes comparing with control group but the dense collagenous fibers at the interfollicular space outside the membrane. Immunostaining of proliferating cell nuclear antigen[PCNA], which reflects the growth fraction, showed 2.3% positivity of total follicular cells in control group. The PCNA positive ratio in experimental groups were 10.3%, 15.9%, 19.9%, 12.2%, 10.5%, 1.9%, 2.7% on postoperative 1, 2, 3, 4, 5, 7, 10 days respectively. In unilaterally thyroidectomized rats, the resected lobe revealed 18.2% of PCNA positive ratio 3 days after operation, while that in the unresected lobe was only 5.9%. This suggested the predominence of local factors in thyroid regeneration. Meanwhile, with the double immunostaining of calcitonin and PCNA discriminate between follicular cells and C-cells among the PCNA positive cells, PCNA positive C-cells were very rare. The immunostaining of laminin, fibronectin, and collagen IV showed varying intensity with the progress of regeneration. Stainability for collagen IV was maintained in all groups with some increase in 5- and 7-day groups. Laminin was well localized to the basement membrane of the control follicle, and the staining intensity for laminin was markedly increased with additional cytoplasmic staining in follicular cells in 1- to 3-day groups and then decreased to attain the control level in 10-day group. In case of fibronectin, the control follicle showed scarce staining, but the resected group showed strong positivity for fibronectin with the most intense staining in 1- to 3-day groups. Immunostaining for fibronectin still showes in 10-day group with the gradual disappearance of immunoreactivity in the center of the lobe. This study revealed the accompaning changes of the basement membrane components during the regeneration process of partially resected thyroid glands. Among them, collagen IV seems to support the structural integrity of the basement membrane. Laminin and fibronectin were supposed to be related to the thyroid follicular regeneration.