Endocrine Abstracts

Thyroid C-cells, as a second type of endocrine cell population within thyroid, produce and secrete peptide hormone calcitonin (CT). This hypocalcemic hormone acts as an inhibitor of bone resorption. The aging is a complex process that alters various cellular functions. Therefore, the aim of this study was to examine the aging-related changes in the structure and function of CT-producing thyroid C-cells in male Wistar rats, using histomorphometric, ultrastructural and biochemical analysis. The investigation was performed on three groups of male rats: adult (3-months old), middle-aged (16-months old) and old (24-months old). The peroxidase-antiperoxidase method was applied for localization of CT in the C-cells. Stereological analysis was performed using Olimpus microscope (BX-51), equipped with a microcator, a motorised stage and a CCD video camera, and controlled by the newCAST stereological software package. Blood serum samples were analyzed for determination of CT, testosterone (T), calcium (Ca²⁺) and phosphorus (P) concentrations. We found a significant increase in the volume density (Vv) of thyroid C-cells in both middle-aged and old rats, all compared to adult animals. The percentage of smaller volume range C-cells (<500 μm³) increases, while the proportion of greater volume rang C-cells (both 500-1000 μm³ and >1000 μm³) markedly decreases with aging. By ultrastructural analysis we found that the average number of secretory granules per C-cell was significantly increased in both middle-aged and aged rats, all compared to adults. Unlike the C-cells of adult rats, these granules in older, especially in old animals, had a content of fairly low density. By the biochemical analysis, we detected a significant increase in serum CT levels, while serum T was markedly reduced in both middle aged and old rats, all in comparison with adults. Serum Ca²⁺ concentration significantly decreased in middle-aged rats compared to adults, while concentration of serum Pwas lower in both middle-aged and old rats, all related to adult group. Our findings show that aging process increases the Vv of thyroid C-cells, with a simultaneous change in percentage of cells with larger and smaller volume rang, and an increase in the number of both cell types. These changes, accompanied by modulation of the cellular ultrastructure and an increase in serum CT levels, reflect the structure and function of CT-producing thyroid C-cells in our aging model.