Multi-frequency bioimpedance measurements of children in intensive care

Bioimpedance spectroscopy is used to monitor the condition of the tissues of children staying in intensive care for the treatment of meningitis. The results are significant, with the angular frequency at maximum reactance lying between 1500 and 6400 x 10(3) rads(-1), whereas in a control group, this value does not exceed 900 x 10(3) rads(-1). The ratio between the specific conductance at zero and that at infinite frequency (this ratio is proportional to total body volume/volume of extracellular space) remains constant at 1.4 and equal to the ratio in the control group, despite infusions with physiological saline. The electrical parameters are associated with physiological ones and indicate that the membrane 'capacitance' decreases, as a result of the illness, from approximately 0.4 in the control group to 0.05 in the patient group. However, there is a time-delay between the onset of illness and the change in membrane capacitance. It is also found that the ratio between extracellular and intracellular specific conductivity in the group of patients and controls remains constant at approximately 4.3. The changes in the physiological and electrical parameters were compared with chemical parameters that were measured during the stay in intensive care.

The value of dextran 12,000 in ischemically damaged canine kidneys during machine perfusion

The use of non-heartbeating (NHB) donor kidneys has led to the search for new methods of viability-testing. We investigated, in a canine model, the relationship between the filtration of dextran 12, 000 into urine and a certain period of warm ischemic time (WIT) during machine perfusion. Twenty-four canine kidneys were divided into three groups, sustaining 0 min, 30 min or 60 min of WIT. After cooling and flushing, the kidneys were perfused on a perfusion machine for 8 h. Three hundred milligrams of dextran 12,000 was added to the perfusate. In the perfusate, dextran and lactate dehydrogenase (LDH) concentrations were measured. Dextran concentrations were also analysed in urine. Intrarenal vascular resistance (IRR) was calculated from pressure and flow characteristics. The 30WIT group showed a higher dextran excretion rate than the other two groups. IRR and LDH measurements showed lower levels in the ischemic groups compared with the control group. Dextran 12,000 is not suitable as a viability test but does show interesting results regarding the low LDH and IRR levels in the ischemic groups.

Glutamine: the pivot of our nitrogen economy?

Glutamine serves as a shuttle of useful nontoxic nitrogen, supplying nitrogen from glutamine-producing (eg, muscle) to glutamine-consuming tissues. True production rates of glutamine are difficult to measure, but probably are less than 60 to 100 g/d for a 70-kg man. During catabolic stress increased amounts of glutamine are released from muscle, consisting of protein derived glutamine, newly synthesized glutamine, and glutamine losses from the intramuscular free pool. The large and rapid losses of free muscle glutamine are difficult to restore, presumably as a result of disturbances in the Na+ electrochemical gradient across the cell membrane. Whereas increased amounts of glutamine are released from muscle, glutamine consumption by the immune system (liver, spleen) also is enhanced. Thus, during catabolic stress changes occur in the flow of glutamine between organs. These changes are not necessarily reflected by alterations in the whole-body appearance rate of glutamine. In contrast with the gut, where glutamine is taken up in a concentration dependent manner, the immune system actively takes up glutamine despite decreased plasma concentrations. Supplementation with glutamine influences uptake by both the gut and the immune system, as evidenced by increased mucosal glutamine concentrations and gut glutathione production. There is evidence suggesting that this improves gut barrier function. Although the benefit of glutamine supplementation is most evident from experimental studies, clinical studies on the effect of glutamine do exist and suggest that glutamine supplementation has beneficial effects with regard to patient outcome.

A new method for plasma volume measurements with unlabeled dextran-70 instead of 125I-labeled albumin as an indicator

A method has been developed to determine plasma volume with dextran-70 without the use of a fluorescent label. The results obtained are compared to those found using the 125I-labeled albumin method, which is taken as the gold standard. The CV of the method is about 5%, compared to 3% with the gold standard. It is shown to be of use for the determination of an increase in plasma volume during pregnancy.

Mechanism of volume adaptation in the awake early pregnant rat

The objective of the present study was to determine whether the increase in plasma volume (PV) during pregnancy is established by fluid retention or by a shift within the extracellular fluid volume (ECFV) from the interstitium toward the intravascular compartment. To this end, we simultaneously, measured total body water, (TBW), ECFV, and PV together with the hematocrit (Hct) and plasma osmolality 4, 8, and 12 days postsurgery in chronically instrumented pregnant (P) and nonpregnant (NP) rats. The P rats were instrumented with a catheter in the femoral artery on day 1 postconception. In the NP group, neither TBW nor ECFV and PV had changed consistently on days 8 and 12 postsurgery relative to day 4. In contrast, in the P animals, TBW, ECFV, and PV had increased by 16, 24, and 20%, respectively, by day 12 relative to day 4. To evaluate whether PV had increased in concert with an overall rise in TBW or as a result of a fluid shift at the cost of the interstitial fluid volume, we calculated the relative size of each fluid compartment on three consecutive measurement sessions. In the NP group, TBW, presented as percentage of maternal weight (%MW) as well as ECFV (%TBW) and PV (%ECFV) had not changed consistently throughout the measurement period. In the P animals, TBW (%MW) was slightly higher on day 12 compared with day 4, but ECFV (%TBW) and PV (%ECFV) had not changed significantly. Finally, in the NP group, Hct had not changed, whereas, in the P animals, Hct was 10% lower on days 8 and 12 compared with day 4. Plasma osmolality did not change consistently in either group during the course of the experimental period. The gradual synchronous increase in all fluid compartments, without consistent change in their relative distribution, suggests that, in normal rat pregnancy, PV expansion is primarily achieved by fluid retention rather than by a redistribution of the ECFV.

Determination of total body water by multifrequency bio-electric impedance: development of several models

Multifrequency bio-electronic impedance analysis (MF BIA) measurements are taken from a heterogeneous group of patients, varying in size between obese and slim. The measuring system uses four electrodes: two current and two potential electrodes. Three new models are developed to calculate total body water (TBW) from the BIA data, and the resulting TBW values are compared with TBW determined by D2O dilution. The results demonstrate that the most simple model provides the best TBW values. For individual patients, TBW can be determined by means of bioimpedance measurement with an accuracy of 3 litres. In the most simple model (model 1), the body is electrically represented by a cylinder, and corrections are made for the amount of fat. This is an extension of the model used by Xitron. In the more advanced models (2 and 3), the body is represented by a cylinder for the trunk, and truncated cones represent the arms and legs. In model 2, delta TBW amounts to 3 litres. It is shown that the resistance of the trunk is proportional to the square root of the length. In model 3, it is assumed that subcutaneous fat is a poor conductor of electric current. An equation is developed that describes the partition of subcutaneous fat, and the fat layer is then removed from the cones representing arms and legs and from the cylinder that models the trunk.

Gut permeability, intestinal morphology, and nutritional depletion

Nutritional depletion increases the risk for postoperative complications. The intestinal barrier may be important in the underlying pathophysiologic mechanism. In this study, 26 patients were evaluated to determine whether nutritional depletion was related to gut integrity and intestinal morphology. Nutritional depletion was estimated by calculating percentage ideal body weight (PIB) or percentage ideal fat free mass (PIFFM). To assess gut integrity, a lactulose/mannitol (L/M) test was performed. Duodenal biopsies were taken, and villous height, crypt depth, number of IgA-producing plasma cells, intraepithelial lymphocytes (IELs), and proliferating index were determined. The L/M ratio was increased, and villous height was decreased in depleted patients. Depletion was not associated with differences in the number of immune cells or proliferating index. The number of IgA-producing plasma cells was positively correlated with the L/M ratio. This study shows that nutritional depletion is associated with increased intestinal permeability and a decrease in villous height.

Glutathione S-transferase as predictor of functional outcome in transplantation of machine-preserved non-heart-beating donor kidneys

Non-heart-beating (NHB) donors are a valuable source of kidneys for transplantation. The organs, however, sustain substantial warm ischemic damage that may jeopardize the transplantability and result in nonfunction of the grafts. Quantification of warm ischemic time (WIT) and prediction of transplant outcome are essential for the use of NHB donor organs. During machine preservation (MP) the viability of NHB donor kidneys was evaluated through calculating intrarenal vascular resistance and determining lactate dehydrogenase and alpha-glutathione S-transferase (alphaGST) in the perfusate. Thirty-seven functioning (F) and nine nonfunctioning kidneys (NF) were compared. WIT was longer in NF; serum creatinine, donor age, and preservation time were not different. WIT correlated well with alphaGST after 4 and 8 hr of MP (r=0.353, P=0.009, and r=0.346, P=0.011, respectively). When compared with F, intrarenal vascular resistance was increased in NF after 4 and 8 hr of perfusion (P<0.05); at all time points, alphaGST levels were elevated in NF (P<0.05). Lactate dehydrogenase activity was not different between the groups, but could identify immediate functioning grafts within the F group. In conclusion, alphaGST levels correlated strongly with WIT and were also able to distinguish NF from F grafts. alphaGST can adequately predict the functional outcome of NHB donor grafts before transplantation; levels of alphaGST can be used to define reliable safety margins for viability. Therefore, MP is useful in evaluating the viability of NHB donor kidneys, and the parameters discussed will help to select nonviable grafts from this valuable pool of kidneys for transplantation.

An improved bromide assay for the estimation of extracellular water volume by capillary gas chromatography

A sensitive bromide determination has been developed that consists of the following steps: isolation (purification) of bromide; oxidation of bromide to bromine with potassium permanganate and subsequent reaction with acetone, to give the volatile bromoacetone; quantification of bromoacetone by capillary gas chromatography. The method can also be used with small sample volumes appropriate for paediatric applications. Thermodynamic arguments are used to calculate the equilibria involved. The accuracy and reproducibility of the method have been determined. Finally, the bromide space of six volunteers was determined and the clearance of the bromide by the kidneys was investigated.

Glutamine and the preservation of gut integrity

Parenteral glutamine dipeptide improves nitrogen balance in postoperative patients on total parenteral nutrition (TPM). Animal studies show that the structure and function of the gut is preserved by glutamine. It is not known if this is the case in human beings. 20 patients admitted to hospital for total parenteral nutrition were randomly allocated to receive parenteral nutrition enriched with glycyl-L-glutamine (Gln TPN), or standard parenteral nutrition (STPN). Mucosal biopsy specimens were taken from the second part of the duodenum before starting parenteral nutrition, and after two weeks. The ratio between the urine concentrations of lactulose and mannitol after enteral administration was used to measure intestinal permeability. After two weeks of parenteral nutrition in the GlnTPN group, intestinal permeability was unchanged, whereas permeability in the STPN group increased. Villus height was unaltered in the GlnTPN group but in the STPN group it decreased. The addition of glutamine to parenteral nutrition prevents deterioration of gut permeability and preserves mucosal structure.

Circulatory models in assessment of cardiac enzyme release in dogs

Cardiac ischemia causes interstitial leakage of cellular enzymes followed by release of these enzymes into plasma. Quantitative interpretation of these data requires a specific circulatory model, and the performance of such models was investigated. Plasma activities of cardiac enzymes were measured for increasingly abrupt forms of ischemic heart injury in the dog: 1) permanent ligation of the left anterior descending coronary artery (LAD); 2) reperfusion after 2 h of ligation of the LAD; and 3) calcium-free perfusion of the LAD during 10 min (calcium-paradox injury). Release into plasma of a rapidly (41%/h) and a slowly (2.2%/h) catabolized enzyme was calculated from the plasma activities, using a detailed circulatory model with compartments for heart, plasma, muscle, skin, and viscera. The time course of cellular enzyme leakage into interstitial space in the heart was calculated from release into plasma and a range of reported values for transendothelial permeability. Simplification to one- and two-compartment models introduced, respectively, 10 and 2% error in calculated cumulative release. Considering the other sources of error, this implies adequate performance of the two-compartment model. Protein washout from the heart is strongly influenced by expansion of interstitial protein space with dead myocyte volume and depends on the microheterogeneity of necrotic tissue areas. Accelerated release of enzymes into plasma after reperfusion reflects accelerated cellular leakage rather than enhanced washout.

A network thermodynamic model of the concentrating properties of the rabbit/rat kidney in the steady state using the electronic network simulation program SPICE

A model for the simulation of the diluting and concentrating properties of the rabbit and rat kidney is developed. Translation of the physical model into an electronic one brings the model into a form that can be handled by the electronic network simulation program SPICE. The steady state responses of both kidneys to various inputs are calculated under certain conditions.

Estimation of fetal lung maturity by assessment of lamellar body particle concentration

The concentration of lamellar bodies expressed as the optical density at 700 nm in amniotic fluid samples was calculated after centrifugation of the samples to obtain the lamellar bodies in a relatively pure form. The lamellar body concentrations obtained were compared with lecithin-sphingomyelin (L/S) ratios from the same samples. The advantages of the method compared with the L/S ratio are discussed as is the dependence on total volume that the method shares with all other procedures which depend on the measurement of a single concentration.

Role of maternal glucose as a metabolic substrate for the guinea pig conceptus

Our study in pregnant guinea pigs was designed to determine whether the modest fractional contribution of glucose to the late-pregnant uterine caloric uptake was due to inadequate uterine glucose supply or to diminished uterine glucose demand. To this end, uterine uptake of glucose, O2, and lactate was measured in 27 late-pregnant guinea pigs with a wide range of litter sizes. A group of 11 mid-pregnant guinea pigs served as a reference. The fractional uterine uptake of glucose in mid- and late-pregnancy was 90 and 45%, respectively, confirming the indirect data calculated from different studies. In late pregnancy, uteroplacental blood flow (microspheres, -40%) as well as arterial glucose concentration (-30%) had decreased relative to mid-gestation, giving rise to a 60% lower wt-specific uterine glucose supply and a 21% lower wt-specific uterine glucose uptake. Inasmuch as fetal and placental glycogen stores become rapidly depleted after the 50th day of pregnancy, the lower uterine glucose uptake in late pregnancy appears to reflect inadequate uterine glucose supply rather than diminished fetal glucose demands. In late pregnancy, uterine caloric demand per kg is about 60% more than in mid-gestation, most likely associated with accelerated fetal fat accretion. Inasmuch as the latter appears to be mostly fueled by nonglucose fat precursors, it could explain why the glucose fraction of the uterine caloric uptake in late pregnancy has decreased by 50% instead of 21% as compared to mid-gestation. The reduction in arterial glucose concentration in late pregnancy was independent of litter size suggesting this phenomenon is to be a maturational adaptation rather than a sign of inadequate maternal glucose production.

Serum water determination by means of microwave evaporation

A novel method is described for the determination of serum water using a microwave oven. The sources of experimental errors were analysed. Serum samples from two hundred patients were analysed for sodium, water and protein, and the data were used to calculate serum sodium molalities. A possible correlation was investigated between serum water content and protein concentration. The results were compared with those in the literature.

A study of the relationship between placental non-haem iron and iron transfer in the guinea pig: the maturation of the transfer process

The relationship between placental non-haem iron and placental iron transfer has been studied in the guinea pig. From day 25 to day 50, non-haem iron and iron transfer increase. Expressed on placental wet weight or per g of placental DNA, iron transfer and non-haem iron were inversely related; an increase of transfer was accompanied by a decrease of the non-haem iron content. The results are discussed in terms of the hypothesis, that accumulation of non-haem iron in early pregnancy is caused by an imbalance between iron uptake and iron transfer. The steady increase of total non-haem iron till term which has been demonstrated in this study is in contradiction with this hypothesis. The paper describes an alternative hypothesis in which placental non-haem iron, most likely ferritin iron, is assumed to play an active role in the regulation of placental iron transfer.

Movement of oxygen, glucose, and lactate across the uterus of the awake near-term guinea pig

In this study the uterine movement of oxygen, glucose, and lactate was quantitated in the awake late pregnant guinea pig. Mean uterine uptake of oxygen per kg of uterus with conceptus was 581 mumol min-1, which is comparable to the value reported for the awake near-term rabbit, but 30% higher than the value reported for the awake near-term sheep. Experiment-related anemia in some animals was associated with a reduced uterine oxygen uptake. The arteriovenous oxygen difference across the uterus correlated positively with the arterial oxygen content and the hemoglobin concentration and negatively with uteroplacental blood flow. Uterine oxygen uptake showed a positive correlation with both the arterial hemoglobin and the uteroplacental blood flow. Uterine lactate output accounted for 20% of uterine glucose uptake, assuming maternally derived glucose to be the only source for uterine lactate output. After correction for this lactate output, the uterine glucose uptake was 96.5 mumol min-1 X kg-1 of pregnant uterus. This value is 30% higher than in the awake near-term rabbit and more than twice as high as that in the awake near-term sheep. Nevertheless, because of the high uterine demand for substrates, this uterine glucose uptake could only cover 45% of the caloric requirements of the pregnant uterus. The late pregnant guinea pig fetus may derive as much as 55% of its caloric uptake for fat deposition and protein accretion. Therefore, it is likely that the nonglucose uterine caloric uptake in the late pregnant guinea pig consists predominantly of fat precursors and amino acids.

Studies on the mechanisms involved in iron transfer across the isolated guinea pig placenta by means of bolus experiments

Placental binding and uptake of diferric transferrin as well as transplacental iron transfer has been studied in isolated, perfused guinea pig placenta. The process of binding and uptake of transferrin was saturable only on the maternal side. On the fetal side no specific binding occurred. This indicates an asymmetric distribution of transferrin receptors. No receptors are present for albumin, neither on maternal, nor fetal side. Most of the 125I-59Fe transferrin, administered with a single bolus, enters the trophoblast. A small part remains attached to the plasma membranes, as shown by cell fractionation and in transferrin exchange experiments. The majority transferrin, which was internalized, is unlikely to be bound to plasma membranes and may be bound to receptors dissociated from plasma membranes. Based on kinetics of 59Fe appearance and washout at the fetal side of the perfused placenta as a model for trans-placental iron transfer has been postulated. A central feature is the role played by a small compartment (0.14 mumol) to which iron is supplied by a very rapid process at the trophoblast receptor, without internalisation of transferrin. A second un-identified pathway is supposed to regulate the magnitude of the iron transfer pool.

Uterine arterial and venous concentrations of glucose, lactate, ketones, free fatty acids, and oxygen in the awake pregnant guinea pig

The concentration differences across the pregnant uterus of glucose, lactate, ketoacids, free fatty acids (FFA), and oxygen were determined in 21 chronically catheterized guinea pigs. Polyvinyl catheters were inserted into one of the ovarian veins and the right carotid artery around the 50th day of pregnancy. Postoperative recovery of maternal substrate concentrations in this preparation was evaluated in five animals. Elevated hemoglobin and ketoacid concentrations persisted up to the 4th day after surgery in the awake animal. In 16 animals between 54 and 62 days gestation, arterial and venous blood samples were collected between the 4th and 13th postoperative days. Arteriovenous substrate differences across the pregnant uterus (means +/- SD) were as follows: glucose, 0.87 +/- 0.22 mM; lactate, 0.31 +/- 0.11 mM; and oxygen 4.77 +/- 0.58 mM. There was no significant difference for ketoacids. In 10 animals, plasma FFA concentrations were determined. In nine animals, the arterial concentration was higher suggesting a net uptake of FFA by the pregnant uterus. Lactate production by the uterus accounted for approximately 18% of uterine glucose uptake if glucose is assumed to be the only source of uterine lactate production. The mean glucose/oxygen quotient across the uterus corrected for lactate output was 0.92 +/- 0.34. It is concluded that glucose is a major metabolic substrate for the near-term uterus in the pregnant guinea pig and can account for most of the uterine oxygen consumption.

Mechanisms involved in the transfer of calcium across the isolated guinea pigs placenta

The mechanisms of calcium transfer across the trophoblast cells of the guinea pig placenta were investigated. The isolated guinea pig placenta was perfused on both sides with an artificial medium. Uptake and release of 45Ca was studied using different compositions of the perfusion medium. It was found, that calcium enters the trophoblast as a positive ion. Addition of calcium to the perfusion medium caused depolarisation of the cell potential. As a result the uptake of 45Ca decreased when excess calcium was added to the medium. When the NaCl in the medium was replaced by choline chloride or KCl, the uptake of 45Ca was increased, despite depolarisation of the cell potential (van Dijk and van Kreel, 1982). This increased net uptake is probably due to a decrease in the release of 45Ca from the cell. The same effect was observed when KCN or Mg was added to the medium. By inhibiting calcium extrusion at one side of the trophoblast, a net transfer of 45Ca from one side of the placenta to the other side was demonstrated. This transfer occurred against the electrochemical potential gradient and must therefore involve a free energy yielding process.

Iron metabolism and placental iron transfer in the guinea pig

The interrelationship between fetal iron uptake and maternal iron metabolism has been studied in the guinea pig in the course of pregnancy. The rapid increase of the maternal need for iron during the period of fast increasing rates of placental iron transfer is largely compensated for by increased intestinal absorption. No enhanced mobilisation of iron from the liver and spleen iron stores could be demonstrated. The plasma iron turnover, corrected for the transplacental iron transfer rate, remained constant during pregnancy. This means that not only the mobilisation of iron from the stores remains principally unchanged, but also the supply of iron to the maternal organs and tissues. The haemoglobin concentration decreased by about 15% during the period of rapid fetal growth and iron uptake. The maternal blood volume increased during this very period and explained most of the observed reduction. Intestinal iron absorption increases. At day 55 of pregnancy placental iron transfer is maximal. It could be shown that a day 55 the rate of intestinal iron uptake equals the rate of iron transfer across the placentas. It is evident that pregnancy effects a direct influence on intestinal iron absorption, independent of the magnitude of the maternal iron stores. How this influence is realized without changing the iron kinetics of the maternal stores, cannot be explained with the prevailing theory.

Placental transfer and metabolism of purines and nucleosides in the pregnant guinea pig

The placental transfer and metabolism of several purines and nucleosides have been investigated using an artificially perfused guinea-pig placenta. A model describing transfer and metabolism in the uteroplacental unit is constructed and applied. Measurements of oxypurines and guanine have been performed in vivo in the blood of pregnant guinea pigs and their fetuses. It appears that only the oxypurines and, to a lesser extent, guanine are present in the maternal and fetal circulations. These purines could be involved in transfer from mother to fetus and used for salvage in the fetal tissues.

Electric potential differences in the isolated guinea-pig placenta

Knowledge of the magnitude of the electric potential differences between the maternal and fetal circulations and the trophoblast is necessary to describe transport of ions into and out of the trophoblast as it occurs in placental transfer of charged molecules. The value of the electric potential difference is also of significance in describing the transport of neutral molecules when their transport is coupled to electrogenic co-transport systems. We developed a method to obtain the values of these potential differences, in the isolated guinea-pig placenta perfused on both sides with an artificial medium. A positively charged ion that carries a radioactive label is allowed to equilibrate between the trophoblast and its circulations. The intracellular equilibrium concentration can be calculated and, because the extracellular concentration is known, the potential difference can be obtained with the Nernst equation. Rapid equilibrium is obtained by charging the trophoblast by means of perfusion of the placenta with the ion at a high concentration, followed by reduction of the concentration in the medium until equilibrium is observed. This is done in both a continuous and discontinuous manner. In addition to measurements of the potential differences, their origin was investigated. It was shown that at least part of the potential difference is generated by the action of transcellular Na--K exchange, because depolarization could always be obtained by decreasing the transmembrane Na and K gradients. Mean values obtained were delta psi F = 71 +/- 21 mV (+/- SD) for the potential difference between the fetal circulation and the trophoblast and delta psi m = 64 +/- 16 mV for the potential difference between the maternal side and the trophoblast with the cell interior negative.

Hypoxanthine metabolism and transfer in the pregnant rhesus monkey

Fetal metabolic conversion and clearance of hypoxanthine was investigated in five pregnant rhesus monkeys. [14C]hypoxanthine injected into the fetal circulation disappeared rapidly and its metabolic break-down products uric acid and allantoin appeared in fetal plasma and erythrocytes. In amniotic fluid only hypoxanthine could be demonstrated. When [14C] hypoxanthine was infused into the fetal circulation at a constant rate and metabolic conversion to uric acid and allantoin was inhibited with allopurinol, a constant level of hypoxanthine was obtained within 30 min. No uric acid or allantoin was demonstrated, but inosine monophosphate and adenine nucleotides appeared in the fetal erythrocytes. The concentration of adenine nucleotides in the fetal red cells showed a steady increase during the experiments. Total fetal hypoxanthine clearance, calculated in the steady-state from the maternal and fetal arterial concentrations and the amount infused per unit of time varied between 4.2 and 8.4 ml min-1. In two separate experiments maternal blood was incubated with [14C] hypoxanthine and [14C]adenosine. The erythrocytes appeared to be unable to convert hypoxanthine into adenine nucleotides, but adenosine was readily converted into ADP and ATP. There appears to be no preferential uptake of hypoxanthine by the fetal erythrocytes which makes it unlikely that they could serve as carriers in the transport of hypoxanthine.

Fetal and maternal concentrations of uric acid and oxypurines during labor and post partum

Concentrations of uric acid (UA) and oxypurines (OPs) were enzymatically determined in fetal scalp plasma, amniotic fluid, and maternal venous plasma simultaneously collected during oxytocin-induced labor in 19 normal term parturient patients. Values were compared with concentrations in arterial and venous cord plasma and maternal plasma drawn immediately post partum. During labor until just before delivery fetal levels of UA were significantly lower and OP concentrations were significantly higher than the corresponding maternal levels. These differences were absent when cord and maternal concentrations were compared. It is concluded that UA and OP values in cord plasma do not reflect fetal levels during labor. The cause of this discrepancy remains obscure.

Maternal and umbilical plasma concentrations of uric acid and oxypurines at delivery in normal and hypertensive pregnancy

Concentrations of uric acid (UA) and oxypurines (OP) were enzymatically determined in arterial and venous cord plasma, and in maternal plasma at delivery in normal (n = 45) and hypertensive (n = 22) pregnant women. Concentrations of UA in all samples were significantly higher in hypertensive than in normal pregnancies. Concentrations of OP in hypertensive pregnancies showed a nonsignificant increase as compared with normal pregnancies. There were no significant differences between concentrations of UA or OP in paired samples of arterial or venous cord plasma and maternal plasma. This finding suggests an easy transfer of UA and OP across the placenta during labor, which is at variance with earlier experimental data obtained in the pregnant rhesus monkey. The hypothesis is put forward, that labor and delivery could influence the facility of placental transfer of UA and OP.

Transport and accumulation of alpha-aminoisobutyric acid (A.I.B.) in the guinea pig placenta

Active transport of A.I.B. from mother to fetus was studied. This was done in the intact animal and using the isolated placenta, artificially perfused at both sides. It was shown that A.I.B. is actively accumulated in the placental cells. An estimate of the kinetic constants is given. It is shown that this accumulation takes place predominantly from the maternal side of the placenta. A.I.B. that has been accumulated is cleared to the maternal and fetal circulation in equal amounts. So the netto active transport from mother to fetus is brought about by an unequal distribution of carriers, the maternal side being most active.

Transfer and dynamics of uric acid in the pregnant rhesus monkey. I. Transplacental and renal uric acid clearances

Data from the literature suggest that uric acid produced by the fetus could pass across the placenta and contribute to the observed increase in maternal plasma levels of uric acid in preeclamptic pregnancy. To investigate this hypothesis, fetal transplacental and renal uric acid clearances were estimated in 4 term pregnant rhesus monkeys by means of the steady infusion method using 14C-labeled uric acid. Allantoin clearances were determined in one pregnant monkey. Samples of maternal and fetal arterial blood were collected at regular intervals. The total amount of fetal urine produced during the experiment was collected at the end of the experiment. In addition, maternal endogenous renal uric acid and creatinine clearances were measured in 6 term pregnant monkeys. Fetal transplacental uric acid clearances appeared to be almost entirely limited by placental permeability and varied between 3.6 and 8.6 ml X min-1 X kg-1 of fetal weight; fetal renal clearances were between 0.11 and 0.20 ml X min-1 X kg-1. The allantoin clearances were found to be of the same magnitude. Maternal renal clearances of uric acid and creatinine were almost equal (mean 3.2 +/- 0.6 and 3.0 +/- 0.5 ml X min-1 X kg-1 of maternal weight, respectively). Extrapolation of these data to human preeclamptic pregnancy reveals that it is unlikely that fetal uric acid could significantly contribute to the maternal uric acid load.

Transfer and dynamics of uric acid in the pregnant rhesus monkey. II. A mathematical model

The objective of the present study was to develop a mathematical model of the dynamics of uric acid between fetal and maternal compartments in the term pregnant rhesus monkey. In 3 different animals 14C-labeled uric acid was injected into the fetal circulation, the amniotic fluid and the maternal circulation, respectively. In one experiment no uric acid was administered and the fetus was deliberately killed at the beginning of the experiment. Samples of fetal and maternal blood, maternal urine and amniotic fluid were collected at regular intervals. Semilogarithmic time-activity curves were constructed and time constants were determined. An open four-compartment model (fetal-placental plasma, fetal-placental interstitial space, amniotic fluid and maternal plasma) was applied to describe the intercompartmental dynamics of uric acid. Transplacental clearance was approx. 1 ml X min-1 in both directions, maternal renal clearance was about 17 ml X min-1. These results and the calculated values of the other intercompartmental clearances support earlier results, obtained with the steady infusion method. Uric acid concentrations in amniotic fluid and fetal plasma appeared to increase significantly during the experiments. The rise in amniotic fluid levels can only be explained by accepting a yet undefined compartment in which uric acid is produced and cleared directly into the amniotic cavity. It is speculated that this additional compartment could be the fetal lung.

Transport of uric acid and hypoxanthine across the isolated guinea pig placenta

Transport of uric acid and hypoxanthine across the isolated guinea pig placenta is investigated quantitatively. The clearances measured are independent of concentration. It is shown that the uric acid transport is not greatly influenced by variations in flow, so it is concluded that the uric acid transport is membrane limited. The clearance of hypoxanthine is even less than the uric acid clearance, so hypoxanthine transport is also membrane limited. Xanthine oxidase is shown to be present in the uterine tissues, and an apparent Km and a maximum velocity have been determined.