Summary
Thirty‐two growing rats were fed restrictively 10 semisynthetic diets which were adjusted to Se contents of 40, 70, 100, 150, 200, 300, 450, 600, 1000 and 3000 ng/g by adding Na selenite. After 3 weeks of collecting the faecal and renal excretions the animals were killed. True absorption and endogenous faecal excretions were determined by the isotope‐dilution technique after an injection of 75Se at day 7 of the experiment.
True absorption and endogenous faecal excretion of Se averaged 96% and 7% of intake irrespective of the Se supply. Renal excretions accounted for 12% of intake between dietary Se levels of 40 and 100 ng/g, increased abruptly to 32% at 150 ng/g, rose degressively to a maximum of 68% at 1000 ng/g and fell to 63% at highest Se intake. The Se retention was proportional to Se intake up to dietary Se levels of 100 ng/g, remained constant up to 200 ng/g and then increased at rising extent as dietary Se rose.
The tissue Se concentrations increased with rising dietary Se contents, especially between 40 and 150 ng/g and between 1000 and 3000 ng/g. The most pronounced changes were observed in the liver which acted as Se storage. In brain, testes and hair the Se concentrations remained constant except at highest Se supply.
Rising Se intake intensified the elimination of injected 75Se mainly via urine and reduced the final whole body 75Se activity from 88% of injected dose at 40 ng/g to 7% at 3000 ng/g. Below 150 ng/g the contribution of liver 75Se to whole body 75Se was reduced in favour of testes and other tissues. At high Se supply, the 75Se contribution of skeletal muscles increased. This may indicate the existence of a slow exchanging or immobile Se compartment within this tissue. The recovery of injected 75Se was complete irrespective of the level of Se supply. Se exhalations were therefore not of quantitative importance.
The GSH‐Px activity in blood plasma increased degressively with rising Se supply. Due to its continuous change the GSH‐Px activity could not be used to identify the transition from a deficient to a sufficient dietary Se supply.
In conclusion, the homeostatic control of Se metabolism is based on the urinary Se excretion. The onset of this regulation at dietary Se levels between 100 and 150 ng/g indicates the transition of a deficient to a sufficient dietary Se supply. The compensatory capacity of Se homeostasis seems to be overloaded at dietary Se contents above 600 ng/g.
Zusammenfassung
Homöostatische Anpassung des Se‐Stoffwechsels sowie des Gewebeselens an eine über einen weiten Bereich hinweg variierende Se‐ Versorgung 75Se‐markierter Ratten
32 wachsende Ratten erhielten restriktiv 10 semisynthetische Diäten, deren Se‐Gehalte mit NaSelenit auf 40, 70, 100, 150, 200, 300, 450, 600, 1000 bzw. 3000 ng/g eingestellt waren. Die Kot‐ und Harnausscheidungen wurden quantitativ gesammelt und die Tiere nach 3 Wochen getötet. Die wahre Absorption und endogene fäkale Exkretion wurde über die Isotopen‐Verdünnungsmethode nach Injektion von 75Se am 7. Versuchstag ermittelt.
Die wahre Abso...
