The effect of fasting and refeeding on thyroid follicule structure and thyroid hormone levels in young and old rats.

In order to assess morphological and functional plasticity of the thyroid gland in aging the effects of fasting and refeeding on the thyroid morphology and thyroid hormone serum levels were compared with morphometry and RIA in young and old rats. Young (4 months) and old (24 months) male Wistar rats were fasted for 40 h and sampled, or fasted and fed thereafter for 4 or 24 h. In control (fed) old animals the thyroid follicules were larger, the follicular epithelium was smaller and colloid resorption was smaller than in young rats.

Thyroid hormones homeostasis in rats refed after short-term and prolonged fasting.

Effects of starvation on thyroid hormone homeostasis were usually determined after 2 or more days of fasting, however, both in man and in rodents, natural feeding cycles comprise far shorter fasting periods. Therefore serum levels of T4, FT4, T3, FT3 and rT3 were measured in rats refed chow diet for 1, 4, 8 or 24 hours after 14 or 48 hours of starvation. Both short-term (14 h) and long-term fasting (48 h) decreased body weight and serum glucose level.