Diffusional resistance of the innermost layer of the placental barrier of the rabbit

Faber, J. Job; Hart, Frederick M.; Poutala, Arnold C.

doi:10.1113/jphysiol.1968.sp008565

Cited by 14 publications

(6 citation statements)

References 20 publications

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“…In the placenta of each of these three species the reflexion coefficients of the placental barrier, even for small solutes, are sufficiently different from zero to cause rapid movement of water across the barrier under the influence of a difference between the osmolarities of the foetal and maternal plasmas. The rabbit placenta, however, is very much more permeable to small solutes such as sodium ion and chloride ion, than the sheep placenta (Flexner & Gelihorn, 1942;Faber, Green & Long, 1971;Faber, Hart & Poutala, 1968;Meschia, Battaglia & Bruns, 1967). Understandably, about half of the increase of plasma osmolarity in the rabbit foetus was found to be due to the transfer of mannitol to the foetal plasma (Bruns et al 1963) whereas the amount of mannitol transferred to the sheep foetus was found to be negligible in the present experiments.…”

Section: Discussionmentioning

confidence: 43%

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Foetal placental blood flow in the lamb

Faber¹,

Green²

1972

The Journal of Physiology

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SUMMARY1. Fifteen sheep foetuses of 1-5-5-2 kg body weight were prepared with indwelling arterial and venous catheters for experimentation one to six days later.2. Unanaesthetized foetuses were found to have mean arterial and central venous blood pressures of 40 + 1-5 (S.E. of mean) and 2x0 + 0-3 (S.E. of mean) mm Hg respectively, compared to intra-uterine pressure. Intra-uterine pressure was 16 + 0-8 (S.E. of mean) mm Hg with respect to atmospheric pressure at mid-uterine level.3. Mean placental blood flow of the foetuses was 199 + 20 (S.E. of mean) ml./(min. kg body wt.). Mean cardiac output in eleven of the foetuses was 658 + 102 (S.E. of mean) ml./(min.kg).4. Mean foetal and maternal colloid osmotic pressures were 17'5+ 0 7 (S.E. of mean) and 20-5 + 0-6 (S.E. of mean) mm Hg respectively at 380 C.5. Intravenous infusions into six ewes of 1P8 mole of mannitol and 0 4 mole of NaCl resulted in significant increases in foetal plasma osmolarity, sodium, potassium, and haemoglobin concentrations, without detectable transfer of mannitol to the foetal circulation.6. In the sheep placenta there is osmotic and hydrostatic equilibration of water. As a consequence, there should be an interaction between foetal placental blood flow and foetal water exchange with the maternal circulation. It was concluded that this interaction tends to stabilize foetal placental blood flow.

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Section: Discussionmentioning

confidence: 43%

“…Tritiated mannitol was counted in a Packard Tri-Carb liquid scintillation spectrometer model 314EX by routine methods (Faber et al 1968).…”

Section: Isotope Analysismentioning

confidence: 99%

Foetal placental blood flow in the lamb

Faber¹,

Green²

1972

The Journal of Physiology

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“…The finding in the present study that the endothelial layer contributes more than half of the total diffusion resistance to ferritin contrasts with our previous findings (5,6) that it contributes only some 5-10% of the total diffusion resistance to smaller molecules. Large molecules are less permeable than small ones because large molecules have relatively smaller coefficients of free diffusion in water (15,16,(21)(22)(23), but if the three layers of the rabbit placenta do not discriminate molecular size, there would be no reason to expect that the relative contribution of any one of these layers changes witlh the molecular size of the diffusing solute.…”

Section: Discussioncontrasting

confidence: 56%

The steady state concentration gradients of an electron-dense marker (ferritin in the three-layered hemochorial placenta of the rabbit.

Thornburg¹,

Faber²

1976

J. Clin. Invest.

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A B S T R A C T Ferritin was injected into the fetal or the maternal circulation of 27-29-day-pregnant rabbits. After the occurrence of a quasi-steady state, the placentas were prepared for electron microscopy. Ferritin particles were counted in the electron micrographs in the fetal capillaries, in the maternal blood spaces, and in the two interstitial compartments of the three-layered placenta. Under the circumstances of the experiments (excessively elevated plasma ferritin concentrations), no evidence was found for nondiffusional transport of radiolabeled ferritin. Comparison of the standing concentration gradients in the placentas, recorded after maternal and after fetal injection, showed that the interstitial spaces "excluded" ferritin; the plasma-interstitial space ferritin partition coefficients were 10 in the basement membrane space and 3 in the space between the cyto-and syncytiotrophoblasts. 55% of the total concentration gradient across the rabbit placenta occurred across the fetal endothelium, about 45% across the cytotrophoblast, and less than 5% across the syncytiotrophoblast. These figures are believed to reflect the relative contributions of these three layers to the total diffusional resistance in the rabbit placenta. When compared to previous data on the relative contributions of these three layers for small ions and molectules, the present data lead to the conclusion that discrimination of molecular size is a function of the fetal capillary endothelium alone. INTRODUCTIONFlexner and his co-workers studied placental permeability to hydrophilic materials in different species.This work appeared partially in abstract form in The Physiologist. 16: 468, 1973. Received for publication 11 December 1975 and in revised form 14 June 1976. This work of the early 1940's led to the generalization that the diffusion resistance of a placenta correlates roughly with the number of placental layers separating fetal from maternal blood (1). Recent electron microscopic studies have shown marked differences in ultrastructure in these layers, even between homonymous layers of placentas of related species (2, 3). It is unlikely. therefore, that further experiments comparing placental permeabilities in different species can bring out the specific properties of the individual histologic layers. It does seem possible, however, to proceed with an orderly characterization of placental permeability if one can compare the diffusion resistances of the individual layers in a given species. For this purpose, we chose the three layers of the hemodichorial placenta of the rabbit.In many hemochorial placentas, a group of placentas including those of man, guinea pig, rabbit, mice, and rats, there are occasional very thin "epithelial plates" (2)(3)(4) thelium on the fetal side and the syncytiotrophoblast on the maternal side, contributing the remainder. In contrast to these previous studies, which relied on transient methods, the present study reports the steady-state concentration gradients across the entire placental barrier....

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“…In our calculation we have not considered fetal capillary endothelial resistance to transplacental solute movement. However, while the vascular endothelium of the haemochorial placenta of the rabbit restricts the transplacental diffusion of larger molecules, such as ferritin (Thornburg & Faber, 1976), its resistance to the permeation of smaller hydrophilic solutes is small (Faber, Hart & Poutala, 1968). Although corresponding data is not available for the human placenta, studies on the structural organization of the paracellular clefts of human placental terminal villous capillaries suggest that the resistance to diffusion of small solutes in capillary endothelium is small also in human placenta (Leach & Firth, 1992).…”

Section: Reflection Coefficientsmentioning

confidence: 99%

Non‐electrolyte solute permeabilities of human placental microvillous and basal membranes.

Jansson

Powell

Illsley

1993

The Journal of Physiology

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1. Permeability to non‐electrolytes of isolated microvillous and basal membranes from human term placenta was measured using stopped‐flow light‐scattering techniques. The studied solutes were urea, ethylene glycol, glycerol, creatinine, erythritol, arabitol and mannitol. 2. At 37 degrees C, permeability of the microvillous membrane to mannitol and urea was 0.30 +/‐ 0.02 x 10(‐6) cm/s (mean +/‐ S.E.M.) and 3.2 +/‐ 0.2 x 10(‐6) cm/s, respectively. The corresponding permeabilities for the basal membrane were 1.2 +/‐ 0.1 x 10(‐6) cm/s (mannitol) and 4.4 +/‐ 0.3 x 10(‐6) cm/s (urea). The basal membrane was substantially more permeable to hydrophilic solutes than the microvillous membrane. This is probably due to differences in lipid composition, as illustrated by membrane cholesterol content, which was found to be approximately 50% lower in the basal as compared to the microvillous membrane. 3. Similarities between permeabilities in placental membranes and lipid bilayers and the linear relationship noted between solute hydrophobicity and placental permeability suggested that solutes permeate both human syncytiotrophoblast membranes by a solubility/diffusion mechanism. In the microvillous membrane this was supported by data obtained for activation energies (> 10 kcal/mol) and reflection coefficients (close to 1). In the basal membrane, low activation energies for glycerol and urea and a low reflection coefficient for urea indicated that these solutes may, in part, share a common pathway with water. 4. It was estimated that the placental permeability to molecules with a molecular weight under 200 observed in vivo can, to a great extent, be accounted for by transcellular permeation.

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Diffusional resistance of the innermost layer of the placental barrier of the rabbit

Cited by 14 publications

References 20 publications

Foetal placental blood flow in the lamb

Foetal placental blood flow in the lamb

The steady state concentration gradients of an electron-dense marker (ferritin in the three-layered hemochorial placenta of the rabbit.

Non‐electrolyte solute permeabilities of human placental microvillous and basal membranes.

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