Biochemical and functional changes during the bovine fetal thyroid development

Relationships between thyroid status, tissue oxidative metabolism, and muscle differentiation in bovine fetuses

The temporal relationships between thyroid status and differentiation of liver, heart and different skeletal muscles were examined in 42 bovine fetuses from day 110 to day 260 of development using principal component analysis of the data. Plasma concentrations of reverse-triiodothyronine (rT(3)) and thyroxine (T(4)) increased during development from day 110 to day 210 or 260, respectively, whereas concentration of triiodothyronine (T(3)) and hepatic type-1 5'-deiodinase activity (5'D1) increased from day 180 onwards. On day 260, high T(4) and rT(3) and low T(3) concentrations were observed together with a mature 5'D1 activity. Cytochrome-c oxidase (COX) activity expressed per mg protein increased at day 180 in masseter and near birth in masseter, rectus abdominis and cutaneus trunci muscles (P<0.05). Significant changes in citrate synthase (CS) activity per mg protein were observed between day 110 and day 180 in the liver and between day 210 and day 260 in the liver, the heart and the longissimus thoracis muscle (P<0.05). Muscle contractile differentiation was shown by the disappearance of the fetal myosin heavy chain from day 180 onwards. A positive correlation (r>0.47, P<0.01) was shown between thyroid status parameters (5'D1, concentrations of T(4) and T(3)) and COX activity in muscles known to be oxidative after birth (masseter, rectus abdominis) but not in liver and heart, nor in muscles known to be glycolytic after birth (cutaneus trunci, longissimus thoracis). A similar correlation was found between thyroid parameters and CS activity in liver and masseter. Results indicate that elevation of plasma T(3) concentrations in the last gestational trimester could be involved in the differentiation of oxidative skeletal muscles.

Ultrastructural localization of thyroid peroxidase, hydrogen peroxide-generating sites, and monoamine oxidase in benign and malignant thyroid diseases

Despite thyroid tissue heterogeneity, biochemical and morphological features have been associated with certain thyroid diseases. We analyzed the ultracytochemical localization of thyroperoxidase (TPO), TPO-associated hydrogen peroxide-generating sites (H(2)O(2) sites), and monoamine oxidase (MAO) in terms of morphology and biochemical TPO activity in abnormal thyroids. We examined 11 cases of nontoxic multinodular goiter, 5 cases of Hashimoto's thyroiditis, 1 case of oncocytic (Hürthle or oxyphilic cell) adenoma, 5 cases of Graves' disease, 4 cases of papillary carcinoma, and 4 cases of perinodular normal tissue. In the perinodular tissue, TPO was detected mainly in the nuclear envelope, rough endoplasmic reticulum (RER), and subapical vesicles, but not in the apical surface. In multinodular goiter, heterogeneous TPO reactivity ranging from almost null to strongly positive was detected in similar locations as in the perinodular tissue, and was absent in the microvilli. Follicular cells from Hashimoto's thyroiditis displayed TPO in the nuclear envelope and the scarce RER. Remarkably, oncocytic cells from both Hashimoto's thyroiditis and oncocytic adenoma, typically packed with mitochondria, displayed evident TPO reaction exclusively in mitochondrial cristae. In Graves' disease, the nuclear envelope, enlarged RER, and apical vesicles were strongly TPO positive, and microvilli also exhibited TPO activity. Papillary carcinoma cells were negative for TPO. The localization and characteristics of TPO activity in the H(2)O(2) sites were similar to that of TPO in all tissues. MAO was positive in mitochondria of perinodular tissues, multinodular goiter, and oncocytes and negative in Hashimoto's thyroiditis and Graves' disease. Interestingly, MAO was intensely positive in the nuclear envelope of papillary carcinoma but unreactive in mitochondria. Biochemical TPO activity was increased in multinodular goiter and Graves' disease. In conclusion, several changes in ultracytochemical characteristics of TPO, H(2)O(2) sites, and MAO were associated with thyroid disease. Nonmalignant oncocytic cells exhibited an unusual mitochondrial location of TPO and H(2)O(2) sites. The distribution of MAO in nuclear envelope of papillary carcinoma cells could be a further feature of malignancy.