The action of Ca2+ on H2O2 formation catalyzed by an NADPH‐dependent H2O2‐generating system was studied in a thyroid particulate fraction. It was shown that H2O2 formation was inhibited by EGTA and restored in the presence of micromolar concentrations of free Ca2+, and that Mg2+ was unable to restore the activity of the EGTA‐inhibited particulate fraction. Consequently, NADPH‐dependent H2O2 formation requires Ca2+, and the Ca2+ stimulation of this process is specific and reversible.

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In this study, it is shown that NADPH iodination occurs in a thyroid peroxidase-H2O2 system in presence of thyroglobulin, the normal iodination substrate. Previous data suggested that thyroid H2O2 generation is a NADPH-dependent system. Present results support the concept of a compartmentalization of the sites of NADPH oxidation and peroxidasic iodination.

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Neurological endemic cretinism is highly prevalent in severe endemic goiter areas. Often associated to euthyroid goiter, it is probably related to iodine deficiency. However the exact pathogenetic mechanism is yet unclear. We report the biochemical study of thyroid tissue obtained from a 26 year-old female cretin with a grade III multinodular goiter, neurological signs and euthyroidism. After surgery, thyroid tissue was analysed: iodoproteins where characterized by gel filtration, electrophoresis, sedimentation coefficient and antigenicity. Iodoalbumin was predominant while thyroglobulin was quantitatively reduced and poorly iodinated. In vitro, iodination with hog thyroid peroxidase was normal. There was no difference in peroxidase affinity for iodide in the oxidation reaction but a significantly reduced ability to iodinate in vitro thyroglobulin and free tyrosine. Oxidation of acetyltyrosilamide into bityrosine was also markedly reduced. These abnormal findings are known to occur in sporadic cases with or without hypothyroidism. The neurological defects could be linked to transient hypothyroidism during the critical period of nervous system maturation, however a role of iodine deficiency per se cannot be ruled out.