Abstract
Thyroid function decreases and cold exposure response becomes impaired with increasing age. We investigated the age-related changes in thyroid structure and function and cold-induced changes in the thyroid activity of aging rats. Thirty-two male Sprague–Dawley rats were randomly divided into four groups (8 rats per group): young (7 months) and old (22 months) groups exposed to room temperature and cold stress. The active follicle ratio and serum free T3, T4 and TSH, and TSH receptor (TSHR) concentrations in the thyroid tissues of the rats from each group were compared. At room temperature, old rats had significantly lower active follicle ratio and free T3 and T4 concentrations than young rats. Furthermore, old rats displayed higher TSH level than young. Exposure to cold temperature led to significantly increased active colloid ratio and free T3 and T4 concentrations among old rats, but no significant differences were found among young rats. Additionally, no significant changes in the TSH and TSHR levels were observed after cold exposure in both young and old rats. Old rats have lower thyroid function than young rats under normal temperature. Aging rats are more susceptible to cold stress than young rats, and cold-induced thyroid activation occurs independently of TSH.We investigated the age-related changes in the thyroid structure and function and cold-induced changes in the thyroid activity of aging rats. Aging rats have structurally less active thyroid follicles and functionally lower thyroid hormone levels than young rats. Furthermore, old rats are more susceptible to cold stress than young rats, and cold-induced thyroid activation occurs independently of TSH.
Highlights
Control of the body temperature based on the surrounding environment is essential for proper physical activity performance and survival
When we examined the structure of the basic thyroid follicle at room temperature, the follicular cells of young rats formed a thick cuboidal shape, and the colloids were not remarkably large (Figure 1A)
We found that the active follicle ratio and free T3 and T4 concentrations all increased after cold exposure in old rats, their values were still lower than those of young rats
Summary
Control of the body temperature based on the surrounding environment is essential for proper physical activity performance and survival. Similar to the other endocrine organs, the thyroid gland deteriorates with age, and subclinical thyroid dysfunction frequently occurs in the elderly [9, 10]. Such a decrease in thyroid function in the elderly can be assumed to be related to the cause of decrease in heat production. The authors hypothesized that age-related thyroid dysfunction may be associated with the poor ability of elderly individuals to control their body temperature compared with young people and changes in the thyroid function after cold exposure would be different between the elderly and young people. We examined the age-dependent changes in the structure and function of the thyroid gland and compared the changes in the thyroid activity between the old and young rats after cold exposure
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