Placental Handling of Zinc in the Guinea Pig

Simmer, Karen; Dwight, Julia; Brown, Iain; Thompson, R. P. H.; Young, Melissa

doi:10.1159/000242162

Cited by 23 publications

(13 citation statements)

References 13 publications

(15 reference statements)

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“…This could arise if the binding proteins in the tissue take up or release zinc by mass action. This conclusion is in agreement with Simmer et al 1985).…”

Section: Discussionsupporting

confidence: 93%

“…The maternal aspect of the placenta could be the principal barrier to materno-fetal transport of zinc. In studies on the guinea-pig such transfer occurred against a concentration gradient and when placental zinc levels exceeded those in fetal and maternal plasma (Simmer et al 1985). The maternal surface appeared to be rate controlling and it was concluded that zinc is taken up by active transport at the maternal surface of the placenta and released across the fetal surface by diffusion.…”

Section: Introductionmentioning

confidence: 99%

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The Transfer of Zinc Across the Term Dually Perfused Human Placental Lobule

et al. 1988

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SUMMARYNet zinc transfer between fetal and maternal circulation has been described in the in vitro perfused lobule of the human term placenta. The transfer results in a 3 ItM differential between fetal and maternal perfusates which is comparable to estimated values in vivo. Tissue zinc concentration is more than 10 times perfusate concentration and is correlated with zinc flux across the fetal borders of the lobule. Open-circuit studies on net transport of zinc, and upon flow of 65Zn relative to tritiated water (3H20), indicate these fluxes depend upon the nonprotein-bound (free) zinc gradient across the fetal-facing membranes. On the other hand movement across the maternal surface is not related to diffusion gradients of free zinc and is either independent of, or inversely related to, the level of tissue zinc. It is concluded that the uptake of zinc from the maternal perfusate may be coupled to metabolism, whereas its transfer to fetal circulation is linked to the level of free zinc in the tissue.

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“…This could arise if the binding proteins in the tissue take up or release zinc by mass action. This conclusion is in agreement with Simmer et al 1985).…”

Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

The Transfer of Zinc Across the Term Dually Perfused Human Placental Lobule

et al. 1988

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“…The positive correlation found in our study and by others [6,7] between maternal and cord values of serum zinc, and particularly the higher cord serum zinc that we observed in women with serum zinc in the higher quartile, are consistent with findings in the guinea pig [21], In this animal species, maternal-fetal mass transfer of zinc was directly related to maternal plasma zinc concentrations, being non-saturable even in the upper range of physiological levels. This could be due to a more favorable diffusional placental-fetal gra dient of zinc with increasing maternal circu lating zinc concentrations.…”

Section: Effect O F Maternal Serum Zinc Levelssupporting

confidence: 93%

“…particularly in humans. Transfer seems to depend both on maternal and fetal serum zinc-binding ligands [4], with differences in affinity and concentrations possibly playing a role, as has been in part demonstrated in the guinea pig [21,22], Transfer may also depend on placental uptake, utilization and release to the fetus, related to membrane transport sys tems in the svncytiotrophoblast [23], placen tal zinc-binding proteins [24,25] and placen tal metabolism [26].…”

Section: Effect O F Maternal Serum Zinc Levelsmentioning

confidence: 90%

“…These mechanisms probably operate at the maternal surface [21,23] considered to be the limiting step of zinc transfer to the fetus, cou pled with placental metabolism [26], The fi nal transfer of zinc to the fetus seems to occur by simple diffusion down a concentration gra dient [21], dependent on the nonproteinbound zinc across the fetal-facing membranes of the placenta [26].…”

Section: Effect O F Maternal Serum Zinc Levelsmentioning

confidence: 99%

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Maternal, Placental and Cord Zinc Components in Healthy Women with Different Levels of Serum Zinc

Zapata

Melo

Donangelo³

1997

Neonatology

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Serum zinc is known to decrease during pregnancy, but the range of individual values at the end of normal gestation may be considerably large, with uncertain physiological significance in terms of maternal zinc status and maternal-fetal transfer of zinc. In this study we compared several maternal and cord blood indices of zinc status, placental zinc, placental metallothionein and the relationship between maternal, cord and placental components, in 40 healthy pregnant women at delivery with different levels of serum zinc. Subjects were divided into three groups according to serum zinc using as cutoff points the lower and upper quartile values [LZn, < 7.6 µmol/l (n = 10); MZn, 7.6–10.7 µmol/l (n = 20), and HZn, > 10.7 µmol/l (n = 10)]. Habitual zinc intakes were similar in all groups (average 11.5 mg/day). Considering all women, maternal serum and erythrocyte zinc correlated significantly (r = 0.40; p = 0.021). Maternal erythrocyte zinc was higher (p < 0.01) in HZn compared to the other groups. Maternal and cord values of serum zinc correlated significantly (r = 0.43; p = 0.006). Cord serum zinc values were very similar in LZn and MZn but were higher (p < 0.01) in HZn. Cord erythrocyte zinc levels were similar in all groups and about 20–25% of the maternal values. Cord erythrocyte metallothionein levels were also similar in all groups and similar to maternal values. Comparing the percentage distribution of zinc in maternal and cord serum fractions, major differences were observed in HZn, with zinc in albumin fraction being 70% in cord compared to 56% in maternal serum. There was a higher (p < 0.01) percentage of zinc bound to α₂-macroglobulin fraction in maternal serum of HZn compared to maternal serum of the other groups. Maternal and cord zinc in the albumin fractions correlated significantly (r = 0.48; p = 0.002) particularly in HZn (r = 0.71; p < 0.021). Placental zinc correlated negatively (r = ––0.34; p = 0.035) with zinc in the maternal α₂-macroglobulin fraction, but did not relate to placental metallothionein, which had similar levels in all groups (average 0.28 nmol/g wet tissue). Placental zinc levels were lower (p < 0.01) in HZn. Our results indicate that high levels of maternal serum zinc in healthy women at delivery may be related to maternal tissue zinc redistribution that could favor diffusional components of maternal-fetal transfer of zinc.

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Uptake of125I-labelled α2-macroglobulin and albumin by human placental syncytiotrophoblast in vitro

et al. 1998

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We have investigated the binding and internalization of alpha2-macroglobulin and serum albumin by human placental syncytiotrophoblast cells in vitro. The time course (obtained at 4 degrees C) of alpha2-macroglobulin binding indicated that an equilibrium was reached after 4 h. The binding of 125I-labelled alpha2-macroglobulin to syncytiotrophoblast cells was competitively reduced in the presence of excess unlabelled alpha2-macroglobulin. When the concentration-dependence of binding was examined over a wide concentration range, non-linear regression analysis yielded a Kd of 6.4 nM. In the case of albumin, binding was weak and ligand dissociated from the cell surface during aqueous washing making it impractical to analyze the binding reaction. In other experiments, syncytiotrophoblast cells were incubated with 125I-labelled alpha2-macroglobulin at 37 degrees C. Under these conditions, trypsin-resistant cell-associated radioactivity increased with time consistent with ligand internalization. 125I-labelled-ligand was internalized with a t1/2 of about 5 min. After a lag period some radioactivity was released back into the incubation medium. When measured at times up to 210 min, this was found to consist of mostly TCA-precipitable material that had been lost from the cell surface. However, when the incubation was extended to 24 h, almost 15% of the initial cell-associated radioactivity was released to the extracellular medium as TCA-soluble material, consistent with a slow rate of ligand degradation. The specific binding of 65Zn-labelled alpha2M was similar to that of the 125I-labelled ligand and trypsin-resistance measurements provided evidence of alpha2M-mediated 65Zn uptake. These results support a role for syncytiotrophoblast in the metabolism of alpha2-macroglobulin during pregnancy and are also consistent with a role for alpha2-macroglobulin in the maternal-fetal transport of zinc.

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Placental Handling of Zinc in the Guinea Pig

Cited by 23 publications

References 13 publications

The Transfer of Zinc Across the Term Dually Perfused Human Placental Lobule

The Transfer of Zinc Across the Term Dually Perfused Human Placental Lobule

Maternal, Placental and Cord Zinc Components in Healthy Women with Different Levels of Serum Zinc

Uptake of125I-labelled α2-macroglobulin and albumin by human placental syncytiotrophoblast in vitro

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