A total of 89 animals were used. The exposure group consisted of 47 and the control group of 42 animals. To investigate in vivo recovery periode of thyroid gland the animals were divided into four groups differing in the time point of sacrifice after exposure: group 1) sacrificed the day after exposure, group 2) sacrificed one week, group 3) two weeks and group 4) sacrificed three weeks after electromagnetic field exposure.
Histological analyses showed that the volume density of follicular epithelium and thyroid activation index (ratio of the volume density of follicular epithelium to the volume density of colloid) decreased, while the volume density of colloid and capillary network increased in group 1, 2 and 3. However, the values of all these parameters in group 4 were similar to corresponding control group.
Serum T3 and T4 concentrations were significantly lower in exposed animals of group 2-4 compared to control group.
Results demonstrate that after significant morphophysiological changes caused by extremely low frequency electromagnetic field exposure thyroid gland recovered morphologically, but not physiologically (hormone level), during the investigated recovery period.