Identification of albumin as the plasma carrier for zinc absorption by perfused rat intestine

Smith, Kenneth T.; Failla, Mark L.; Cousins, Robert J.

doi:10.1042/bj1840627

Cited by 73 publications

(24 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Placental uptake of zinc and its transfer to the fetus may also be influenced by protein binding in both maternal and fetal plasmas [6]. The importance of albumin in plasma has been demonstrated for the lumen-to-serosal transfer across the isolated perfused rat intestine [14]. The small back flux of zinc from fetus to mother demon strated in our preparation confirms the ob servations of Terry et al [ 10].…”

Section: Discussionsupporting

confidence: 79%

Placental Handling of Zinc in the Guinea Pig

et al. 1985

View full text Add to dashboard Cite

The distribution of zinc between the mother and the fetoplacental unit, and its placental transfer, were studied using stable and isotopic zinc in unanaesthetized pregnant guinea pigs and an in situ perfusion preparation. The concentration of stable zinc in fetal plasma and skeletal muscle was higher than that in the maternal tissues: 2.0 compared with 1.4 μg/ml and 84 with 49 ng/mg dry weight, respectively. The placenta and maternal and fetal liver had similar zinc concentrations: 90, 75 and 88 ng/mg dry weight, respectively. The ability of the placenta to concentrate ⁶⁵Zn, measured 1 h after a single intravenous injection into the unanaesthetized mother, was comparable with that of the maternal liver. Maternal-fetal mass transfer of zinc was directly related to maternal plasma zinc concentrations from 0.7 to 24.1 μg/ml (b = 2 ng·min^––¹·g^––1·μg^––1, r = 0.92). At physiological plasma levels, the calculated transfer would supply the fetus with 0.12 mg zinc/day, similar to the accretion rate over the last trimester. Placental transfer of zinc was not influenced by the concentration of zinc in the placental perfusate. Extraction of zinc from the perfusate was also slow, and partly by absorption. Matemofetal transfer of zinc was directly related to both uterine and umbilical blood flows. The high concentration of zinc in the syncytium, relative to both maternal and fetal plasma levels, suggests active uptake at the maternal surface, combined with a slow release into the fetus, down a concentration gradient.

show abstract

Section: Discussionsupporting

confidence: 79%

Placental Handling of Zinc in the Guinea Pig

et al. 1985

View full text Add to dashboard Cite

show abstract

“…However, a substantially higher percentage of Cu should be bound to albumin in the portal blood because it appears that this protein is responsible for the initial transport of Cu to the liver after absorption by the intestine (36). The same was previously demonstrated for Zn (37,38). This suggests that a more physiological approach to the role of Zn and Cu on hepatocyte MT regulation occurs when the metal is presented to the hepatocyte bound to the physiological chelator(s1.…”

Section: Discussionmentioning

confidence: 57%

Role of extracellular zinc and copper on metallothionein regulation in cultured rat hepatocytes

1991

View full text Add to dashboard Cite

Cellular and extracellular metallothionein contents of rat hepatocytes cultured in the presence of albumin (30 pmoVL) with zinc (1,10,50 and 100 pmol/L), copper (1, 10 and 50 pmol/L), zinc and copper (1, 10 and 50 pmol/L of each metal) or no metals in the culture medium have been measured by radioimmunoassay. Cellular metallothionein levels increased steadily with culture time regardless of the metal treatment and showed little dependence (only a twofold increase) on extracellular zinc or copper at all metal concentrations and times (up to 3 days) studied. In contrast, the presence of both metals simultaneously in the culture medium strongly increased cellular metallothionein contents, acting synergistically in some cases. Significant extracellular metallothionein was observed when copper or zinc and copper were present in the culture medium, most of which is likely a consequence of cell leakage because no evidence of physiological secretion was observed. Total metallothionein production (cellular and extracellular metallothionein levels) indicated that copper was a better metallothionein inducer than zinc in these experimental conditions. These results indicate that metallothionein regulation in the hepatocyte is different depending on the extracellular metal levels and composition and that attention must be given to metallothionein release from the hepatocyte. (HEPATOLOGY 1991;14:648-654.)The liver is believed to be a central organ in zinc (Zn) and copper (Cu) homeostasis in the organism (1, 2). To characterize how the liver regulates the metabolism of these essential heavy metals, the use of cultured hepatocytes has proved to be a useful tool. Several comprehensive studies on the hepatocyte metabolism of Zn and Cu have been published (3-11). In these studies metallothionein (MT), a low molecular weight heavy metal-binding protein, was usually considered to play a central role. However, its levels were either not measured or measured by rather insensitive or nonspecific The putative secretion of MT by cultured hepatocytes has never been studied in detail. This is noteworthy because experimental studies suggest a normal presence of circulating MT (12-21), the source of which, at least in part, might be the liver (22). Biliary excretion of MT has also been reported (16, 23). Studies on the putative secretion of MT by hepatocytes therefore are needed to establish such a possibility.Therefore the aim of this work was to study the effect of physiological (10 p,moliL) and nonphysiological (0, 1, 50 and 100 FmoVL) concentrations of Zn and/or Cu in the culture medium (in the presence of the physiological chelator albumin) on hepatocyte MT content and the putative MT secretion in those conditions (the terms physiological and nonphysiological for metal concentrations are relative; see Discussion). MATERIALS AND METHODSIsolation and Maintenance of Hepatocytes. Isolated liver parenchymal cells were prepared from adult male Lou rats by using the three-step perfusion technique of Garvey and Heil (24) as modified from Seglen ...

show abstract

“…None of the other changes in serum Zn, serum Cu or albumin were different among treatments. Serum albumin is considered m be the primary carrier of readily available Zn in the body (Smith et aL, 1979). Because no differences were observed among treatments for changes in serum albumin, any differences in performance or blood criteria apparently were not due to differences in amounts of carrier proteins.…”

Section: Resultsmentioning

confidence: 99%

Zinc-Amino Acid Complexes for Swine

Hill

Peo²,

Lewis

et al. 1986

Journal of Animal Science

View full text Add to dashboard Cite

Two experiments were conducted to determine the effect of sources of dietary zinc on gain, feed conversion and blood and bone traits of swine. In the first experiment 96 pigs were used in a 28-d study. The pigs were fed diets with no supplemental Zn or with either 9 or 12 ppm supplemental Zn from zinc sulfate (ZnSO 4), zinc methionine (ZnMet) or zinc methionine with picolinic acid (ZnMet w/PAL each with or without 5% added corn oil. There were differences (P<.05) in average daily gain (ADG) and average daily feed intake (ADFI) between the pigs fed the two organic Zn sources, with those fed ZnMet w/PA showing the better gains and feed conversion.However, neither organic Zn source resulted in pig performance that was different from either the diet with no supplemental Zn or the diets supplemented with Zn from ZnSO 4. In the second experiment the same dietary Zn sources and treatments were fed as in Exp. 1 except that corn oil was deleted as a variable. No differences in ADG, ADFI, feed/gain (F/G) or in changes in serum Zn or Cu were observed among treatmerlts during either the 21-d nursery or the 56-d growing periods. During the subsequent 56-d finishing period ADG and ADFI were greater (P<.01) for pigs fed the Zn-supplemented diets than for those fed the diets without supplemental Zn. There were no differences among treatments in F/G during the finishing period. Zn content of bone ash was lower (P<.01) in the non-Zn-supplemented pigs. These data suggest that the Zn sources used are of similar biological value and do not support the theory that picolinic acid aids Zn absorption.

show abstract

Identification of albumin as the plasma carrier for zinc absorption by perfused rat intestine

Cited by 73 publications

References 14 publications

Placental Handling of Zinc in the Guinea Pig

Placental Handling of Zinc in the Guinea Pig

Role of extracellular zinc and copper on metallothionein regulation in cultured rat hepatocytes

Zinc-Amino Acid Complexes for Swine

Contact Info

Product

Resources

About