Diffusion artefacts and tissue fixation in thyroperoxidase cytochemistry.

Area of Science:

• Cell Biology
• Histology
• Biochemistry

Background:

• Endogenous peroxidase activity is crucial in thyroid hormone synthesis.
• Its precise localization within thyroid follicle cells is not fully elucidated.
• Understanding peroxidase distribution aids in comprehending thyroid physiology.

Purpose of the Study:

• To investigate the subcellular distribution of endogenous peroxidase activity in rat, mouse, and human thyroid follicle cells.
• To characterize the nature of the peroxidase reaction product at the apical plasma membrane and its extension into the colloid.

Main Methods:

• Electron microscopic cytochemistry using 3-3'-diaminobenzidine (DAB) staining.
• Comparative analysis across rat, mouse, and human thyroid tissues.
• Evaluation of enzyme activity sensitivity to fixation conditions.

Main Results:

• Peroxidase activity was detected at the apical plasma membrane and in intracellular compartments in all three species.
• Apical membrane enzyme activity was more sensitive to fixation than intracellular activity.
• A gradient of reaction product extended from the apical membrane into the thyroid colloid, suggesting diffusion from membrane-bound enzyme.

Conclusions:

• Endogenous peroxidase is present on the apical plasma membrane of thyroid follicle cells in multiple species.
• The observed gradient in the colloid originates from membrane-bound peroxidase, not soluble enzyme.
• This localization is significant for thyroid hormone production and secretion processes.