The Diffusibility of Oxygen Across the Sheep Placenta

Abstract

Estimates have been made of: (1) the oxygen tension in blood samples drawn from unanesthetized ewes and their fetuses via chronic catheters in the uterine vein, umbilical artery and umbilical vein between 90 days and full term; (2) the rate of oxygen uptake by the umbilical circulation between 80 and 134 days in a series of anesthetized ewes, and (3) the 'diffusing capacity' of the placenta for oxygen in eleven anesthetized ewes in stages of gestation from 81 to 134 days. The results demonstrate: (1) there is no regular change with advancing gestation in the oxygen tension of the blood in the vessels sampled, and (2) the quantity of oxygen taken up by the umbilical blood and the 'diffusing eapacity' of the placenta for oxygen both increase as the fetal weight.As we explained earlier our interest in the permeability of the placenta of the ewe to oxygen, in the period 80 days to full term, grew out of two conflicting lines of evidence. One suggests that the permeability of the placenta and the weight of the cotyledons both reach a maximum about 100-110 days, the other that the permeability to oxygen increases with the fetal requirements as gestation advances beyond the 100th day. Data bearing on the question have been obtained through observations on: (1) the transplacental difference in oxygen tension; (2) the rate at which oxygen crosses the placenta relative to the fetal weight, and (3) the 'diffusing capacity' of the placenta for oxygen. These data are complementary and taken together support the second alternative. MATERIAL AND METHODS(1) The Transpiacental Difference in Oxygen Tension. -Pure bred Dorset ewes, at known stages in gestation, were used in all the experiments reported here. The uterine and umbilical bloods for the estimation of the transplacental difference in P02 were obtained via indwelling catheters [Meschia et at., 1959;.For each estimation two samples were drawn from a single vessel, one of 1-6 ml. into 0-4 ml. of an isotonic heparin-fluoride mixture, a second of 2 ml. (4 ml. from a maternal vessel) into an oiled glass syringe. The pH of the first was measured at room temperature with a glass electrode and a Beckman meter (model G); the result was corrected to 380 by subtracting 0*015 pH units for each degree below 380 at which the measurement was made. The oxygen content of the second sample was determined in duplicate on 0*5 ml. with the Van Slyke-Neil apparatus. The oxygen capacity was.calculated from the optical density at 530 my, of blood diluted 1 to 250 parts with distilled water and alkalinized with ammonia. The colorimeter was standardized with sheep blood saturated with oxygen in a Barcroft tonometer before the content * U.S.P.H. Fellow -present address:

Placental Evolution within the Supraordinal Clades of Eutheria with the Perspective of Alternative Animal Models for Human Placentation

“…Such techniques allow repeated sampling from nonanesthetized animals free of surgical stress in order to obtain data on fetomaternal exchange processes, placental gas exchange, and fetal oxygen supply, under in vivo conditions and experimental manipulations [68,71,138,139,142,143]. The oxygen consumption of the placenta as a highly metabolically active organ is between half and 80% of the total oxygen uptake by the gravid uterus, mainly used for oxidative phosphorylation of glucose [141][142][143]. Indeed, about 80% of the uteroplacental glucose uptake is consumed by the placenta and not transferred to the fetus [144].…”

The Regional Distribution and Determinants of Myocardial Blood Flow during Asphyxia in the Fetal Lamb

“…Glycosylation of Hb occurs by a nonenzymatic reaction that is continuous throughout the lifespan of the red blood cell (8). It follows that g1yco Hb levels will reflect the time-averaged blood glucose level over a period of [8][9][10][11][12] weeks (16,20). This has led to increasing interest of the clinicians in the study of the g1yco Hb levels in relation to diabetes mellitus (14,15).…”

The effects of maternal hypercapnia on foetal oxygenation and uterine blood flow in the pig.

“…Since then this gradient has been studied in other animals and in man, and extensively reported in the literature. Meschia, Cotter, Breathnach & Barron (1965) studied the sheep and Barron & Battaglia (1955) the rabbit. The condition in the rhesus monkey was described by Hellegers, Meschia, Prystowsky, Wolkoff & Barron (1964) and that of the human by Prystowsky (1957).…”