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Iodinated particles in the rat thyroid. II. Lysosomal characteristics
Acta Endocrinologica
|July 1, 1975
Summary
Thyroid gland iodinated particles are identified as secondary lysosomes involved in iodine secretion. Their activity, influenced by TSH and iodine intake, supports thyroid hormone regulation.
Area of Science:
- Endocrinology
- Cell Biology
- Biochemistry
Background:
- Previous studies established methods for isolating iodinated particles in rat thyroids.
- The precise nature and function of these particles remained to be fully elucidated.
Purpose of the Study:
- To further investigate the characteristics of thyroid iodinated particles.
- To determine if these particles function as lysosomes and their role in iodine metabolism.
Main Methods:
- Analysis of acid phosphatase and iodine co-sedimentation.
- Assessing latency changes with hypo-osmotic dilution and pH alteration.
- Evaluating sensitivity to Triton X-100.
- Measuring butanol-extractable iodine (BEI) fraction.
- Observing effects of TSH stimulation, thyroxine treatment, and varying iodine diets.
Main Results:
- Iodinated particles exhibit lysosomal properties: latency, pH sensitivity, and Triton X-100 sensitivity.
- The BEI fraction indicates intralysosomal thyroglobulin hydrolysis via acid protease activity.
- TSH stimulation increases iodine and acid phosphatase; thyroxine decreases them.
- Iodine pool, acid phosphatase, and BEI fraction vary with dietary iodine.
Conclusions:
- Thyroid iodinated particles are secondary lysosomes involved in TSH-controlled iodine secretion.
- These lysosomes hydrolyze thyroglobulin and are regulated by TSH and iodine availability.
- Colloid droplet accumulation occurs primarily after significant TSH stimulation.