Lack of Effect of Oxygen Tension upon the Permeability of the Guinea Pig Placenta to d(+)xylose and Sorbose

Abstract

The rate a t which different sugars cross the placenta varies from sugar to sugar. The aldoses glucose and d( +)xylose are exampIes of rapidly crossing sugars, whereas the ketohexoses sorbose and fructose pass the placenta slowly. It has been assumed that the permeability of the placenta to d( + )xylose is of a similar nature as that to glucose; the permeability to sorbose is comparable with that to fructose (KARVONEN et al., in press). D( + )xylose and sorbose may thus be used as tracer analogues to glucose and fructose, respectively, due to the inability of the organism to metabolize the foreign sugars.The purpose of the present study was to compare the placental permeability of sugars under normal conditions t,o those existing when the mother is kept under hypoxia or hyperoxia, by making it breathe different oxygen-nitrogen mixtures. Material and Nethods.Guinea pigs were used as experimental animals. They were anaesthetized with Nembutal intraperitoneally. The foetuses were delivered through caesarean section into a 0.9 yo NaCl bath kept at 38" C, where they remained connected with a functioning placenta. The foetuses were weighed after the experiment; their exact age was not known.

The placental transfer of hexoses and polyols in the guinea‐pig, as shown by umbilical perfusion of the placenta

“…Most workers agree that, far from being a simple diffusion, placental passage of sugars is either an active process or one of facilitated transfer, as proposed by Widdas (1952). Karvonen, Laamen & Raiha (1956) reported that reduced 02 tension has no effect on transplacental sugar passage, which suggests that an active transfer is not involved.…”

The transfer of free α‐amino nitrogen across the placental membrane in the guinea‐pig

“…These observations are in keeping with those of others on the transport of metabolites and electrolytes by foetal and placental tissue. Wilson & Lin (1960) demonstrated that L-tyrosine is transported anaerobically by the small intestine in the foetal and new-born rabbit for some weeks after birth; Karvonen, Laamanen & Raiha (1956) showed that the placental transfer of D-xylose and sorbose from the foetal to maternal circulation was not influenced by hypoxia, though Lumley & Wood (1967) found that maternal hypoxia did, apparently, decrease transfer ofglucose from mother to foetus in the human subject. Whittam (1960), studying kidney slices, found that sodium, potassium and water concentrations were well maintained under anaerobic conditions in the immature and new-born rabbit and rat, in comparison with the corresponding adult tissue and the more mature new-born guinea-pig.…”

Transplacental xylose transfer in bovine pregnancy

“…Results from studies in humans [18] and rats [32] have verified the materno-fetal unidirectional nature of xylose placental transfer, where xylose accumulation in the uterine compartments, including the fetus, closely reflects its transport. Conversely, results obtained from guinea pigs [22] and sheep [31] suggested the existence of a feto-maternal transfer. By the examination of the transplacental xylose transfer in bovine pregnancies, the aims of this study, were (a) to evaluate the rate of plasma xylose disappearance in pregnant and nonpregnant females, (b) to verify the existence of a feto-maternal transplacental xylose transfer, and (c) to assess the materno-fetal placental permeability to xylose.…”

“…Xylose may be used as a tracer analog to circumvent this problem, since glucose and xylose enter cells by sharing components of the glucose transporter system [29,31]. Both molecules are rapidly transported across the placenta, and placental permeability to both sugars is assumed to be similar [18,22]. The exact mechanism of transplacental xylose transfer is not understood, but a carrier-mediated mechanism has been proposed for the sheep and rat placenta [31,32].…”

“…The exact mechanism of transplacental xylose transfer is not understood, but a carrier-mediated mechanism has been proposed for the sheep and rat placenta [31,32]. Under physiological conditions, xylose is slowly metabolized [8,37], enabling its use for the study of transplacental substrate transfer in humans [18], guinea pigs [22], sheep [31], and rats [32].…”