The metabolism of [75Se]selenomethionine in four women

Abstract

1. The long-term fate of an oral dose of [⁷⁵Se]selenomethionine was studied in four women.2. Urinary and faecal excretion, respiratory losses and whole-body retention of ⁷⁵Se were measured, and also ⁷⁵Se turnover in whole body, plasma and erythrocytes during a period of 33–44 weeks.3. Intestinal absorption of [⁷⁵Se]selenomethionine by the four subjects was 95.5–97.3% of the administered dose.4. Urinary excretion accounted for 6–9% of absorbed ⁷⁵Se in the first 2 weeks. No radioactivity was detected in expired air.5. After the initial 8 weeks during which radioactivity decreased more rapidly, whole-body retention of ⁷⁵Se decreased exponentially with a half-time of 207–290 d.6. Plasma ⁷⁵Se concentration reached a maximum level 3–4 h after the dose. Transient initial uptake of ⁷⁵Se in erythrocytes during the first hour was followed by a gradual increase to a maximum concentration at 8–12 weeks.7. These results are compared with the results of an earlier study of the metabolism of [⁷⁵Se]selenite in two of the same women. ⁷⁵Se from [⁷⁵Se]selenomethionine was found to be more completely absorbed, had a greater retention and smaller endogenous urinary and faecal losses than ⁷⁵Se from [⁷⁵Se]selenite, and these differences persisted throughout the experimental period. These findings differed from those obtained in rats in which, after an initial period, ⁷⁵Se from selenite was metabolized similarly to that from selenomethionine.