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Small-intestinal absorption of cadmium and the significance of mucosal metallothionein

Walther-Straub-Institut für Pharmakologie und Toxikologie der Ludwig-Maximilians-Universität München, Nussbaumstrasse 26, D-80336 München

GJ Strugala

Walther-Straub-Institut für Pharmakologie und Toxikologie der Ludwig-Maximilians-Universität München, Nussbaumstrasse 26, D-80336 München

SG Schäfer

Pharmakologisches Institut der Universität Hamburg, Universitätskrankenhaus Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany

1 Although food intake is among the most important routes of Cd exposure, not many details are known about the intestinal absorption mechanisms of Cd. In this respect Cd is representative of most other nonessential, merely toxic metals.

2 Based on a concept of two distinguishable steps, intestinal absorption of Cd is characterized by high accumulation within the intestinal mucosa and a low rate of diffusive transfer into the organism.

3 After uptake into the mammalian organism, Cd is sequestered into hepatic metallothionein (MT). It is assumed that hepatic Cd-MT then gradually redis tributes Cd to the kidney, which is the main target organ for chronic Cd toxicity.

4 When feeding low levels of dietary CdCl₂, however, Cd accumulates preferentially in the kidney and to a lesser degree in the liver, a distribution pattern also found after intravenous and peroral administration of the Cd-MT complex itself. As dietary Cd induces intestinal MT, intestinal Cd-MT complexes could be at least partly responsible for the renal accumulation of dietary Cd.

5 For this mechanism, however, serosal release of mucosal Cd-MT is required. In fact, in vitro findings in rats reveal a concentration-dependent release of intestinal MT to the serosal side of the small intestine. These results indicate that endogenous intestinal MT may deliver Cd-MT to other inner organs, thus contributing to the preferential renal accumulation of ingested Cd.

Key Words: cadmium • in vitro • rat • renal uptake • small-intestinal metallothionein • small-intestinal absorption

Human & Experimental Toxicology, Vol. 16, No. 8, 429-434 (1997)
DOI: 10.1177/096032719701600803


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