A comparison of the metabolism of intravenously injected sodium selenite, sodium selenate, and selenomethionine in rats

Abstract

Rats were injected with Se⁷⁵-sodium selenite, Se⁷⁵-sodium selenate, and Se⁷⁵-selenomethionine, and the distributions of Se⁷⁵ in tissues, and in proteins isolated from plasma, liver supernatants, and kidney supernatants, were studied as a function of time.

The livers of rats injected with selenite had a much greater initial Se⁷⁵ concentration than those from rats receiving selenate. Kidneys of rats injected with selenite had a peak Se⁷⁵ concentration in the sample taken 1 hr after injection; this was followed by a rapid decline. Kidneys from rats injected with selenate had an almost constant Se⁷⁵ level in all samples from 1 hr to 7 days. In other tissues the Se⁷⁵ activities for rats injected with selenite were similar to those for rats injected with selenate. As has been reported elsewhere the tissues retaining the highest Se⁷⁵ levels were the livers, kidneys, and adrenals.

Rats injected with selenomethionine contained greater Se⁷⁵ concentrations in the pancreas than rats injected with selenite or selenate.

Dialysis of plasma and liver and kidney supernatants against isotonic saline showed that at 1 hr after injection selenomethionine was associated with protein to a greater extent than was selenite or selenate. Disulphide-cleaving reagents (mercaptoethanol and cysteine) and urea were effective in releasing Se⁷⁵ from liver, kidney, and plasma proteins from rats injected with either selenomethionine, selenite, or selenate.

Se⁷⁵ distribution patterns in liver, kidney, and plasma proteins separated by gel filtration or disc-electrophoresis were very similar for samples collected at 1 day, 3 days, and 7 days after injection of rats with either selenite, selenate, or selenomethionine. If, as has been proposed, selenium from selenite or selenate is present in protein as selenotrisulphide, this finding suggests that selenomethionine may not be incorporated into protein intact.