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Pregnant rats were submitted to a selenium\x=req-\ deficient diet immediately after mating; it was continued for 4 weeks after delivery. The pups were sacrificed at 3 and 4 weeks of age. Perchlorate, an antithyroid agent inhibiting iodide trapping in the thyroid, was administered via the drinking water to half of the rats. Rats submitted to a normal laboratory diet and to the experimental diet supplemented with selenium were used as controls. The effects of selenium deficiency were an increase in the number of growth abnormalities, growth retardation, and decreased seleno-dependent glutathione peroxidase (GSH-Px) activity in plasma and in various organs. These effects were relieved by selenium supplementation in the diet. Perchlorate treatment induced the classic picture of primary hypothyroidism. Selenium deficiency increased thyroid hormone levels in perchlorate-treated rats and in controls drinking tap water. In the latter group, it also decreased TSH plasma concentration and thyroid weight. These effects were partially reversed by Se supplementation. In vitro experiments, performed on adult rats, revealed increased radioiodide uptake and organification in glands from the rats submitted to the selenium-free diet. Plasma T3 half-life was similar in control and Se-deficient rats. These data suggest a higher efficiency of thyroid hormone synthesis in the thyroids of selenium-deficient rats, despite a lower thyroid stimulation as evaluated by serum TSH. They are compatible with the hypothesis that decreased selenium supply, leading to a decreased GSH-Px in the thyroid, increases hydrogen peroxide steady state level and thus thyroid peroxidase activity and thyroid hormone synthesis.

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Die Umsetzung der Thioketone (I) mit CH, N2 führt zu Gemischen aus den Thiiranen (II) und den Methyl‐alkenyl‐sulfiden (III); (IIIb) liegt als E‐2‐Isomerengemisch (1:1) vor.

Carbon-13 N M R spectra of various aliphatic ketones and tbioketones were determined and interpreted. As shown by the relation between OC chemical sbifts in C=A groups, the C=S is more sensitive to the substituents than the C=O group. Conjugative effects are more pronounced in a-cyclopropyl thioketones than in a-cydopropyl ketones. Compte tenu des remarques suivantes nous avons tent6 de relier So, S, et o, en restant conscient de ce que, en skrie cktonique, les variations AE ont une part non nkgligeable dans les variations de 6 , : RESULTATS ET DISCUSSIONS S6rie aliphatique(1) Pour A fixe (0 ou S) le terme Q, peut Ctre relik h la somme des constantes a, de Taft des substituants X et l'on peut admettre en premikre approximation que ? L a prtsence de radicaux alcoyles au voisinage du groupe carbonyle entraine un kger dtplacement bathochrome de la transition m* + n (Rtf. 5); on peut d'ailleurs relier le dkplacement chimique 6, des cktones aliphatique avec la valeur A,(a* + n) (Rkfs. 6-8). Il n'y a pas de relation directe dans le cas des thiocktones: la position du A,, ne vane pas lintairement avec le nombre de substituants en a (cf. Rtf. 9). Par contre elle varie beaucoup quand on passe d'une &tone la thiodtone homologue. On ne pourra donc pas relier les valeurs SI3C(=0) et 6I3C(=S) en terme de densitt de charge uniquement (cf. Rtf. 2).