The effects of fasting and refeeding on the thyroid follicles of young and aged mice--morphometric analysis

The population movements of thyroid follicles in young and aged mice subjected to acute fasting and refeeding were analyzed by a morphometric method. After fasting for three days, the size distribution of thyroid follicles from young mice did not change, while the follicles from aged mice became significantly bigger than in the control group. Subsequent refeeding for four days caused a decrement in follicular sizes in both young and aged thyroid. The activity of follicular epithelia was decreased by fasting, but accelerated by refeeding. The equation describing the relationship between epithelial cell numbers and follicle diameters from a young control mouse agreed well with the theoretical one, especially in small follicles. However, the equation for an aged mouse differed from the theoretical one. This suggests that the older the mouse, the greater the deviation of the constituent factor, e.g. that of follicle size or cell number in thyroid. The extent of deviation would be one of the characteristics of aging in multicellular organisms.