John M. Bissonnette

Glucose uptake into plasma membrane vesicles from the maternal surface of human placenta

SummaryGlucose uptake into plasma membrane vesicles from the maternal surface of the human placenta was measured with the Millipore filtration technique. Uptake ofd-glucose was dependent on the osmolarity of the incubation medium surrounding the vesicles. Uptake ofd-glucose exceeded that ofl-glucose. The uptake ofd-glucose was not enhanced by placing 100mm NaCl or NaSCN in the medium outside the vesicles (none inside) at the onset of uptake determinations.d-glucose transport was inhibited by cytochalasin B; phloretin, phlorizin, and 1-fluoro-2,4-dinitrobenzene.d-glucose uptake was inhibited by 2-deoxy-d-glucose, 3-O-methyl-d-glucose and to a lesser extent byd-galactose. It was not inhibited by α-methyl-d-glucoside. Cytochalasin B binding to the vesicles was 30% inhibited in the presence of 80mm d-glucose. The results indicate that the system for facilitated transport ofd-glucose at the maternal face of the placenta is distinctly different from that on the brush-border membrane of intestine or renal tubule and more closely resembles that of human erythrocyte.

Gas exchange of the fertile hen's egg: Components of resistance

The resistance to diffusion of respiratory gases falls by 50% from day 10 to day 18 in the incubating fertile hens egg (Temple and Metcalfe, 1970). We have calculated the change in the components of this resistance with respect to incubation age. The egg shell resistance remains unchanged. The chorioallantoic membrane (including capillary endothelium) resistance decreases dramatically from day 10 to day 14 and then remains relatively unchanged. The resistance offered by the blood is unchanged from day 10 to day 12, it decreases by day 14 due to an increase in oxygen capacity and continues to decline at days 16 and 18 because of the combined effects of a continued increase in oxygen capacity and an increase in capillary volume.

Persistent pulmonary hypertension in the neonate: Development of an animal model

Chronic intrauterine hypoxia was induced in third-trimester lamb fetuses by daily embolization of the maternal side of the placenta with nonradioactive microspheres. After delivery at term, the chronically hypoxic fetuses had significantly increased pulmonary artery pressures when compared to nonhypoxic control measurements. This preparation appears to be a satisfactory model for experimental study of persistent pulmonary hypertension in the neonate.

Hen's eggs with retarded gas exchange. I. Chrorioallantoic capillary growth☆

The diffusing capacity of the hens egg for carbon monoxide (D tau co) increases during incubation, reflecting the development of the chorioallantoic circulation. Previous work showed that the increase in D tau co could be diminished by incubating eggs in a 60% oxygen environment. The present work explored the effects of impeding gas exchange on the development of D tau co. Half the shell area was covered during incubation by a removable neoprene membrane which limited D tau co by approximately 20%. No difference could be detected between the D tau co values (measured with the membrane removed) of these eggs and control eggs incubated in the same 21% oxygen environment without a neoprene membrane. We conclude that the development of the chorioallantoic circulation is at its maximum under normal conditions of incubation and cannot be accelerated by restricting gas exchange.

Effect of metabolic acidosis on fetal breathing movements in utero

Abstract Experiments were carried out in 7 unanesthetized fetal lambs in utero in which catheters had previously been placed in the trachea (for intrathoracic pressure measurements), axillary artery (for pH and blood gas determinations), brachial vein (for infusions) and amniotic fluid. Fetal breathing movements (FBM) were noted as negative deflections in intrathoracic pressure recorded simultaneously with intraamniotic pressure and expressed as the incidence per 60-min period, in percent. Intravenous infusion of 0.2 N HCl lowered pH from 7.368±0.012 to 7.128±0.022 (with no significant change in PaCO2) for an 8-hour period. The incidence of FBM did not increase above control levels for the first 4 hours after the initiation of the acidosis. However, in the 5th to 8th hours FBMs occurred 52%, 53%, 59% and 64% of the time, respectively. These are all significantly above the control levels of 23%, 30%, 27% and 21% observed during these same hours on other days in the same animals. We conclude that fetal respiratory activity in utero is stimulated by hydrogen ion (H+) possibly mediated by central chemoreceptive structures.

Placental diffusing capacity for carbon monoxide in unanesthetized guinea pigs

In unanesthetized pregnant guinea pigs 5-7 ml of maternal blood which had been equilibrated with carbon monoxide (CO) was reinfused into the sows carotid artery. Three serial blood samples were withdrawn from the sow and a single terminal fetal sample obtained for determination of CO content and hemoglobin concentration. Transplacental CO uptake (VCO) was determined as the product of fetal blood CO content and fetal CO space (11.8% of fetal weight). Placental diffusing capacity (DPCO) was calculated by dividing VCO by the mean partial pressure difference between maternal and fetal blood. DPCO (ml-min(-1)/torr) increased significantly with gestational age: 45-50 days = 0.0413, 51-57 days = 0.1092 and 58-68 days = 0.1858. This increase paralleled fetal weight but was not related to placental weight.

Placental Diffusing Capacities at Varied Carbon Monoxide Tensions

To test the hypothesis that carbon monoxide transfer across the placenta is, in part, a facilitated process, we have looked for evidence of saturation kinetics for carbon monoxide. In eight pregnant ewes, fetal to maternal carbon monoxide transfer was examined in a preparation in which the fetal side of the placenta was perfused with blood. The carboxyhemoglobin concentrations on the fetal side of the placenta were varied from 4.8 to 70% in 23 measurements. At increased carbon monoxide tensions, the transfer from fetus to mother always decreased. The slope of log rate of carbon monoxide transfer vs. log partial pressure gradient across the placenta was significantly different from 1. Placental membrane diffusing capacity was calculated separately from total placental diffusing capacity which includes hemoglobin reaction rates and erythrocyte membrane diffusion. Placental membrane diffusing capacity decreased at increased carbon monoxide tensions. Placental permeability for urea did not change with increasing carbon monoxide tensions. These results are consistent with the hypothesis that carbon monoxide diffusion in the placenta is, in part, carrier mediated.

The role of a trial of labor with a positive contraction stress test

During a 28 month period 812 patients underwent antepartum FHR testing. Twenty-eight patients had a positive CST. There were two antepartum fetal deaths and 11 patients had a cesarean section without a trial of labor. Fifteen patients had a trial of closely monitored labor (continuous FHR and fetal scalp blood sampling when indicated) and 11 of these (73%) were delivered vaginally. The CST records were examined for: per cent late deceleration, baseline FHR, presence of FHR accelerations, duration of the latency period (time from onset of contraction to onset of deceleration), and amplitude of deceleration. The absence of accelerations (nonreactive CST) and a latency period of less than 45 seconds both predicted persistent late deceleration during labor or fetal death in utero but statistical significance was found only for the latter parameter.

Uterine oxygen uptake in the pregnant pygmy goat

The diffusion equilibrium method was used to measure uterine blood flow (Qut) and oxygen consumption (VutO2) of 7 Pygmy goats in the last third of pregnancy. VutO2 was 9.3 +/- 1.3 (mean +/- SEM) ml.min-1.kg-1 weight of the uterus and its contents: the placenta, fetus and fetal membranes. This O2 requirement was provided by a high blood flow (349 +/- 48 ml.min-1.kg-1) and a narrow arteriovenous difference (2.4 +/- 0.1 vol%) across the uterus. Maternal arterial O2 content (CaO2) was varied by incurring chronic anemia in 3 animals. CaO2 over the range 6.5 - 12.8 vol% did not affect uterine blood flow or the arteriovenous oxygen content difference across the uterus. Weight specific (ml.min-1.kg-1) VutO2 did not differ in animals whose total uterine weights varied over a wide range and uterine vein oxygen tension and content did not fall prior to delivery. We conclude that the absolute uterine blood flow varies over a wide range to meet the requirements of the uterine contents.

A COMPARISON OF CHORIOALLANTOIC AND PLACENTAL RESPIRATION

Publisher Summary This chapter presents a comparison of chorioallantoic and placental respiration. The studies of the dynamics of oxygen supply described in the chapter were started by measuring the total carbon monoxide diffusing capacity of the fertile hens egg, using a preparation that was very simple in principle. Several living eggs at a known stage of incubation were placed in a closed system, containing a CO analyzer. Room air recirculated rapidly through the system. After temperature equilibrium to 38°C had been achieved, a small amount of CO was injected into the recirculating air, and its rate of disappearance was measured. Before the sixth day of incubation, eggs have such a low diffusing capacity that it cannot be measured accurately with this method. However, beginning at the sixth day, satisfactory measurements were obtained. Knowing the relative diffusibilities of O2 and CO, these measurements were translated into values for O2 diffusing capacity (DO2). The chapter also presents a graphical comparison of the oxygen tension gradient between environmental air and the tissues of a mammalian and an avian embryo.