SEASONAL-CHANGES IN THE ULTRASTRUCTURE OF THE THYROTROPH IN THE WOODCHUCK (MARMOTA-MONAX) ADENOHYPOPHYSIS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 130  (MAY) , 499-505
Abstract
Seasonal ultrastructural changes in the thyrotroph of the woodchuck adenohypophysis were studied in correlation with reported data on the thyroid gland and blood thyroid hormone levels in the same animals. Cilia ratios were calculated for each of the 4 seasons and a significantly lower ratio was found in the spring glands. This fact, together with the ultrastructural morphology, indicates an increase in number and activity of the thyrotroph following the hibernation seasnon. The thyrotroph continues to be active through summer, decreasing in activity in the autumn and is in remission during the winter. These findings are reciprocally related to the thyroid follicular cell activity and free serum T3 [triiodothyronine]. Since the winter thyroid and thyrotroph are inactive, the thyroid hormone needed for periodic arousals may be met by conversion of bound T3 and thyroxine to the free mode. The thyroid in hibernating animals appears to be unresponsive to low temperatures.