| Autor: |
SHAW, A J, MUGHAL, M Z, MOHAMMED, T, MARESH, M J A, SIBLEY, C P |
| Zdroj: |
Pediatric Research (Ovid); June 1990, Vol. 27 Issue: 6 p622-625, 4p |
| Abstrakt: |
Mechanisms of maternofetal Mg transfer have been investigated across the in situ perfused rat placenta at 21 d gestation (term23 d). The fetal placental circulation was perfused with Mg-free Krebs-Ringer solution and clearance of Mg from maternal plasma across the placenta unidirectional maternofetal clearance (Kmf) Mg compared with that for 45Ca and 51Cr-EDTA, the latter being used as a diffusional marker. Because diffusion coefficients determined for these solutes were similar (6.8-7.6 X 10~6 cm2-sec−1), greater Kmf values determined for Mg and 45Ca (mean ± SD 26.7 ± 9.2 and 93.1 ± 29.8 nLmin−1-g−1placenta, respectively) compared to 51Cr-EDTA (3.2 0.9 fiLmin '-g ') suggest that maternofetal transfer of these cations occurs by mechanisms in addition to diffusion. Kmf Mg was also greater than Kmf 5ICr-EDTA when measured across the dually perfused rat placenta, in which the maternal uterine artery was additionally perfused with Mg-containing (0.5 mmol-L−1) Krebs-Ringer solution. Decreasing the Mg concentration in the maternal perfusate by 90 reduced Mg appearance in the fetal perfusate by 87 within 8 min; this suggests that Kmf Mg across the in situ perfused placenta largely reflects Mg transfer from maternal plasma and not simply elution of a placental Mg pool. Addition of KCN (1 mmol-L−1) to the fetal perfusate or lowering perfusate temperature from 37 to 26°C significantly reduced Kmf Mg and Kmf 45Ca across the in situ perfused placenta. In contrast, Kmf 51Cr-EDTA was increased by KCN and unaffected by temperature. Both total and ultrafiltrable Mg concentrations were higher in fetal compared with maternal plasma, indicating that maternofetal Mg transfer occurs against a chemical gradient. These data collectively suggest that maternofetal transfer of Mg, as well as that of Ca, is dependent on placental metabolism. (Pediatr Res 27 622-625, 1990 |
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