Changes in serum thyroid hormone levels and urinary ketone body excretion caused by a low selenium diet or silver loading in rats.

Biochemical indices of selenium (Se) deficiency (tissue Se content and glutathione peroxidase activity, serum thyroid hormone level, and urinary ketone bodies during fasting) were measured in rats fed a low-Se diet or rats loaded with silver (Ag). One group of male weanling Wistar rats was fed a casein-based low-Se basal diet (Se content, 0.027 mg/kg). Other groups were fed the basal diet supplemented with sodium selenite (0.2 mg/kg of Se), or silver acetate (250 mg/kg of Ag), or both for 6 weeks. Without silver loading, hepatic and blood Se contents and GSH-Px activities were much lower in the rats fed the basal diet than in the rats fed the selenite-supplemented diet. The Ag loading decreased the Se contents and GSH-Px activities irrespective of dietary Se level. There were significantly higher serum thyroxine (T4) concentrations in rats fed the low-Se diet and in Ag-loaded rats than in rats fed the selenite-supplemented diet without added Ag. Differences in serum 3'-, 5, 3-triiodothyronine (T3) concentration were not significant among the 4 groups. Urinary ketone body excretion was abnormally high in rats fed the basal low-Se diet, but Ag-loading decreased the ketone body excretion; ketone body metabolism in the Ag-induced low-Se state was different from that in the diet-induced low-Se state.