Malabsorption of zinc in rats with acetic acid-induced enteritis and colitis.

Acute intestinal inflammation was established in rats by intraluminal administration of acetic acid into loops of distal ileum, proximal jejunum or ascending colon. The study included two control groups of intact (untreated) rats and sham-operated (saline-treated) rats for each intestinal segment. A third group of rats received acetic acid. Histological evaluation demonstrated that acetic acid treatment induced a mild inflammatory response. Two days after treatment, zinc absorption was measured using ligated 10-cm loops of each segment in which 65Zn was injected intraluminally. 65Zn absorption by the ileum, jejunum and colon was markedly reduced in those rats in which inflammation was induced by acetic acid. The liver showed the highest uptake of radioisotope, but the relative tissue distribution generally followed the amount of absorption. The surgical procedure itself seemed to reduce zinc absorption. No changes in [3H]leucine absorption were observed between sham-operated and acetic acid-treated controls. There was no significant serosal-->luminal secretion of intramuscularly injected 65Zn in any of the studied segments. Therefore, based upon the data obtained, we conclude that acetic acid-induced intestinal inflammation reduces absorption of zinc by the small and large intestine, and that a surgical procedure (laparotomy) also reduces zinc absorption. The mechanism of this inflammation is such that malabsorption shows some specificity.

Regulation of cysteine-rich intestinal protein by dexamethasone in the neonatal rat.

The cysteine-rich intestinal protein (CRIP) is an intestinal zinc-binding protein containing a single copy of a cysteine-rich domain known as the LIM motif. CRIP mRNA and protein levels increased in the rat small intestine throughout the suckling period, reaching highest levels by the late weanling stage. A similar developmental pattern of CRIP protein levels was also detected by an increase in zinc binding to CRIP-containing HPLC fractions of intestinal cytosol. Administration of the synthetic glucocorticoid hormone dexamethasone to neonates caused the precocious rise of CRIP mRNA and protein. In adult rats, CRIP mRNA levels were not significantly altered by dexamethasone. Maximal CRIP mRNA content was detected in cells from the mid-villus, as confirmed by expression of cryptdin mRNA. In this report we show the glucocorticoid regulation of the LIM motif-containing protein CRIP and suggest that glucocorticoid hormones play a role in developmental regulation of CRIP.

Mechanisms of caeruloplasmin biosynthesis in normal and copper-deficient rats.

To examine the mechanisms of holo-caeruloplasmin biosynthesis, we measured the serum caeruloplasmin concentration and oxidase activity, hepatic caeruloplasmin mRNA content and hepatocyte caeruloplasmin biosynthesis and secretion in normal and copper-deficient rats. Copper deficiency resulted in a near-complete loss of serum caeruloplasmin oxidase activity, yet only a 60% reduction in serum caeruloplasmin concentration and no change in the abundance of hepatic caeruloplasmin mRNA or the rate of caeruloplasmin biosynthesis. Both interleukin-1 alpha and lipopolysaccharide increased hepatic caeruloplasmin mRNA content and caeruloplasmin biosynthesis in normal and copper-deficient animals, but neither mediator increased caeruloplasmin oxidase activity in the copper-deficient group. Pulse-chase studies in primary hepatocytes from normal and copper-deficient rats revealed that the secretory rates for newly synthesized caeruloplasmin were identical, despite little or no holo-caeruloplasmin synthesis in hepatocytes of copper-deficient rats. We conclude that hepatocyte copper content has no effect on hepatic caeruloplasmin-gene expression or caeruloplasmin biosynthesis and that the incorporation of copper into newly synthesized caeruloplasmin is not a rate-limiting step in the biosynthesis or secretion of the apoprotein from rat hepatocytes.

Nuclear zinc uptake and interactions and metallothionein gene expression are influenced by dietary zinc in rats.

Regulation of metallothionein gene expression by dietary zinc and the relationship of dietary zinc to nuclear zinc uptake was examined in growing rats. Zinc was fed at 5, 30 or 180 mg/kg, either in pelleted form for a 2-wk period (ad libitum) or for 2 h as a liquefied preparation (1 g in 4 mL). Two hours after the oral dose, the intestine and liver took up more zinc than other tissues. Nuclei purified from liver, kidney and spleen accumulated substantial amounts of zinc and directly reflected the dietary zinc level within the 2-h feeding period. Nuclei from kidney accumulated the largest amount of dietary zinc within 2 h, accounting for up to 6.2% of the total nuclear zinc concentration. Northern analysis demonstrated that metallothionein expression was proportional to dietary zinc intake in some tissues. It was greatest in kidney, followed in descending order by liver, intestine, spleen and heart. Thymus and lung metallothionein mRNA levels were not changed appreciably by dietary zinc intake. Chromatography of extracts from liver nuclei shows that 65Zn introduced into the portal supply is bound to discrete fractions of nuclear proteins. One of these fractions binds both 65Zn and a 32P-labeled oligonucleotide corresponding to the metal regulatory element of the metallothionein promoter. These results demonstrate that significant amounts of zinc from the diet are rapidly taken up by cell nuclei. Furthermore, they suggest that transcriptional regulation of the metallothionein gene and other genes with metal regulatory elements involves a direct interaction between the dietary supply and intranuclear factors that bind zinc.