title: Evidence for active maternofetal transfer of magnesium across the in situ perfused rat placenta.
abstract: Mechanisms of maternofetal Mg transfer have been investigated across the in situ perfused rat placenta at 21 d gestation (term = 23 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 microL.min-1.g-1 placenta, respectively) compared to 51Cr-EDTA (3.2 +/- 0.9 microL.min-1.g-1) suggest that maternofetal transfer of these cations occurs by mechanisms in addition to diffusion. Kmf Mg was also greater than Kmf 51Cr-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 degrees 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.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Child Health, University of Manchester, St. Mary's Hospital, England, United Kingdom.
authors.forename: A J
authors.initials: AJ
authors.lastname: Shaw
authors.forename: M Z
authors.initials: MZ
authors.lastname: Mughal
authors.forename: T
authors.initials: T
authors.lastname: Mohammed
authors.forename: M J
authors.initials: MJ
authors.lastname: Maresh
authors.forename: C P
authors.initials: CP
authors.lastname: Sibley
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000097:blood*; D008431:Maternal-Fetal Exchange / Q000502:physiology*; D010477:Perfusion; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D008274:Magnesium; D002118:Calcium