Abstract
The effects of surgical thyroidectomy on the ultrastructure of the adrenal fasciculata zona of the adult male rat were investigated. In the thyroidectomized rats, the nucleus presented large heterochromatin patches mainly localized at the nuclear periphery and the nucleolus-associated chromatin; the cytoplasmic alterations were scarce. Morphometric studies showed a significant decrease in the relative volume of the nucleus, nucleolus, and euchromatin and a significant increase in the relative volume of heterochromatin. The numerical density of perichromatin granules counted in material prepared by the EDTA method showed a significant decrease. Concerning the cytoplasmic organelles, the morphometric data only revealed a significant decrease in the relative volume and surface density of mitochondria. The nuclear and mitochondrial volumetric changes induced by surgical hypothyroidism may be related to the absence of the thyroid hormone, nuclei and mitochondria probably being the subcellular targets for the thyroid hormone.
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