Uptake of Se75 in tissues of sheep after administration of a single dose of Se75-sodium selenite, Se75-selenomethionine, or Se75-selenocystine.

A total of 34 sheep of both sexes were used in the experiments. Se-selenomethionine in a tracer dose and Se-sodium selenite at three dose-levels (from a tracer dose to a therapeutic dose) were injected by the subcutaneous route. Se-selenocystine in a dose that may be regarded as higher than a therapeutic dose of selenium was given intravenously. Se-sodium selenite in a tracer dose and a therapeutic dose was injected intraruminally. High levels of Se were noted mainly in renal cortex, liver, and adrenal cortex after injection of Se-sodium selenite, whereas the values for skeletal muscle were low. Injections of Se-selenomethionine and Se-selenocystine resulted in higher Se-levels in pancreas than did tracer doses of Se-sodium selenite. The tissues retained a greater percentage of a tracer dose than of a therapeutic dose of Se-labelled sodium selenite, with the exception of the liver, in which the percentage retention was relatively constant, irrespective of the dose level. The amount of Se recovered in the tissues was higher after subcutaneous than after intraruminal injection of a small selenium dose. The Se-levels differed very little or not at all when a therapeutic dose was injected by these two routes. These results suggest that in sheep the storage of inorganic selenium is limited. In most tissues the difference between the Se-concentration at 2 days and that at 13 days was small after subcutaneous injection of a therapeutic dose of selenium. The Se-content in renal cortex, muscle, and lung was higher, however, at 2–8 days than at 13–22 days. It was also higher in the rumen wall at 2 days than later. When Se-sodium selenite was injected subcutaneously, most of the radioactivity in the tissues was present in the protein precipitated with trichloracetic acid, the recoveries in the precipitate being 71–83 per cent at 2 days and 78–94 per cent at 13 days. The proportion of plasma-Se bound with the proteins averaged 53 per cent at 1 hour and 90 per cent at 7 days.