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Biomedical subjects

J J Faber

Publications and source records attributed to J J Faber.

70 records · Page 4Linked to original sources
PubMed1968

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

1. The permeability of the endothelial cell layer of the foetal capillaries of the rabbit placenta was measured by the tracer-dilution method. Isotopically labelled water, urea, chloride and sodium ions, and inulin were used. Radio-iodinated human serum albumin served as reference tracer. The measurements were made in in situ placentas of 27-29 days gestation of which the foetal circulation was perfused with homologous blood.2. The permeability of water was found to be 1.7 ml. min(-1).g(-1), the permeabilities of urea, chloride ions and sodium ions were in the range of 0.28-0.42 ml. min(-1).g(-1) and the permeability of inulin was 0.053 ml. min(-1).g(-1). These values may be underestimates, particularly the value of water.3. The approximate maternal blood space, foetal blood space, and extravascular sodium space were determined in rabbit placentas of 27-29 days gestation and found to be 0.16, 0.07, and 0.48 ml./g respectively.4. The permeabilities of the endothelial layer were compared to those published for the entire placenta and found to be far greater. The resistance to diffusion of the endothelial layer is only a small part of the total resistance to diffusion. Most of the resistance is localized in the syncytioand/or cellular trophoblasts.5. It was concluded that lipid insoluble molecules diffuse through the interstitial water spaces of the trophoblast in few, relatively wide channels but that diffusing water can make use of intracellular as well as extracellular paths.

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PubMedDate not supplied

Electrophysiology of extrafetal membranes.

This paper reviews some of the equations that apply to the electrophysiology of the extrafetal membranes, and stresses the limitations that may apply to the use of these equations. A literature review of experimental data on potential differences between the fetus, the extrafetal fluid compartments and the mother leads to the conclusion that the transplacental potential difference is no more than a few millivolts and that, in some species, there is an electrical generator outside the placenta.

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PubMedDate not supplied

In vivo placental permeability to hydrophilic solutes as a function of fetal weight in the guinea pig.

The permeability of the placenta was measured with unlabelled inulin in unanaesthetized guinea pigs. Inulin was injected into the sows and the plasma concentrations were recorded at regular intervals. The inulin contents of the conceptuses were calculated from fetal weights, fetal plasma inulin concentrations and a measured inulin distribution volume of 180 ml/kg fetus. From fetal inulin contents and the time integral of the difference in maternal and fetal plasma concentrations, we calculated a mean inulin permeability of 29 +/- 9 (s.e.m.) nl/s per gram placental weight. The inulin permeability per gram placental weight rose statistically significantly with increasing fetal weight. Comparison with a similar rise observed for the smaller cyanocobalamin molecule studied previously led to the conclusions that in the last ten days of gestation the transplacental passages narrow while at the same time there are apparent changes in the numbers and/or lengths of these passages that suffice to increase the unrestricted permeability fourfold.

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PubMedDate not supplied

Current topic: water volume of the ovine conceptus; point of view.

The sheep is the only species for which there is sufficient information to justify an overview of maternofetal water transfer. Current information points to the following conclusions: (1) the site of water exchange between mother and conceptus is mainly the placenta; (2) the pressure that initiates transfer to the fetus is the osmotic pressure of solutes that are present in higher concentrations in fetal plasma than in maternal plasma, such as urea, fructose, amino acids, bicarbonate and lactate; (3) maternal ultrafiltrate thus attracted into the conceptus arrives there mostly denuded of electrolytes and is strongly hypotonic; thus it is the transfer of electrolyte that restrains the transfer of water; (4) maternofetal transfer of water is strongly facilitated by angiotensin I in the fetal circulation by a sequence of events that has not yet been elucidated; (5) the net combined osmotic and hydrostatic pressure that drives water across the placenta is of the order of only 20 to 80 mm Hg; (6) it is necessary to make a sharp distinction between transfer from mother to conceptus and transfer from one compartment to another compartment within the conceptus. Finally, the review lists certain precautions to be taken in the further study of water exchange between mother and conceptus.

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PubMedDate not supplied

Flexner's Na+ clearances and the histological structure and age of the placenta in various species.

1939 and the early 1940s saw the publication of a remarkable series of papers on placental transfer. For the first time, a group of investigators made a quantitative and systematic study of the transfer of a simple, presumably inert physiological solute, the sodium ion, in a number of different species at various gestational ages. The driving force behind these studies was Louis Barkhouse Flexner.

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