Effect of hypoxemia on fetal hemoglobin synthesis during late gestation.

This study was carried out to investigate the effect of fetal hypoxemia, as a result of acute intermittent maternal hypoxia, on the switchover from fetal to adult type Hb as well as Hb oxygen affinity and 2,3-diphosphoglycerate levels in the near-term fetus. These experiments were carried out using 10 fetal lambs with gestational ages ranging from 132 to 140 d. After the installation of appropriate fetal catheters, five of the ewes were exposed to an air mixture containing 10% O2 for 90 min/d for 4 consecutive d. Blood samples were withdrawn before the beginning of the hypoxic experiments and between the 5th and 6th d after the first episode of hypoxia. These samples were for the determination of 2,3-diphosphoglycerate concentration, arterial O2 pressure at which Hb is 50% saturated, and Hb type synthesis. Blood gases were monitored during each hypoxic episode. During the hypoxia, fetal arterial O2 pressure decreased from 2.43 +/- 0.36 kPa (18.2 +/- 2.7 mm Hg) to 1.57 +/- 0.17 kPa (11.8 +/- 1.3 mm Hg). These values returned to their initial levels after cessation of the maternal hypoxia. Five control animals of the same gestational age were also followed. During the interval of the study, a decrease of fetal Hb synthesis was noted (71.7 +/- 12.1 to 57.4 +/- 10.2%, p less than 0.001) in the control group. However, the level of fetal Hb synthesis did not significantly change in the hypoxic group (85.1 +/- 11.1 versus 80.6 +/- 18.9%).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated levels of fetal hemoglobin synthesis in infants with bronchopulmonary dysplasia.

A study was devised to determine whether levels of fetal hemoglobin (HbF) synthesis are elevated in infants with bronchopulmonary dysplasia (BPD) when compared with the levels of HbF synthesis found in normal control infants. Twelve infants with BPD, whose postconceptional ages ranged from 40 to 62 weeks, were studied. The mean (+/- SD) gestational age and birth weight was 29 +/- 1.9 weeks and 1289 +/- 376 g, respectively. Elevation infants matched for birth weight, gestational age, and postnatal age served as the control subjects. Blood samples were incubated in an amino acid mixture containing [14C]leucine. The adult hemoglobin and HbF were then separated by column chromatography on diethylaminoethyl-Sephadex. The results demonstrated that the mean (+/- SD) level of HbF synthesis in infants with BPD was significantly higher than that in the control infants (42.6 +/- 22.9% vs 18.8 +/- 12.8%; P less than .01). When levels of HbF synthesis in the infants with BPD and the control infants were compared with data previously reported in normal infants, 7 of the 12 infants with BPD, but none of the control infants, were synthesizing amounts of HbF greater than would be expected for their postconceptional age. The results suggest that cardiopulmonary insufficiency could stimulate HbF synthesis during the first year of life as a result of an erythropoietic response to hypoxemia.

Hemoglobin oxygen dissociation (P50) in bronchopulmonary dysplasia.

A study was devised to determine the P50 in infants with bronchopulmonary dysplasia (BPD). Other factors such as red blood cell 2,3-diphosphoglycerate (2,3-DPG) level proportions of adult (HbA) to fetal (HbF) hemoglobins which could affect P50 were also measured. Fourteen infants with clinical and radiological signs of BPD with a mean post-conceptional age of 42.2 +/- 4.7 weeks born at a mean gestational age of 29.3 +/- 2.0 weeks were evaluated. The percentage of HbF determined in 8 infants was 40.1 +/- 20.3% and the mean 2,3-DPG concentrations was 13.1 +/- 2.2 mumol/g Hb. The P50 was 25.1 +/- 2.7 mm Hg (range 18-29.5 mm Hg). When a HbO2 curve was established based on a large volume of blood consisting of adult blood and newborn cord blood mixed to attain a P50 of 25.1 mm Hg, the PaO2 at 90% O2 saturation was 52 mm Hg. Since there can be a wide range in HbO2 in infants with chronic BPD, pulse oximetry remains the most prudent method of monitoring oxygen therapy in BPD infants.

The inhibition of the postnatal rise of 2,3-diphosphoglycerate in newborn lambs as a result of glucose perfusion.

Due to the abrupt increase in 2,3-diphosphoglycerate (2,3-DPG) concentration in the newborn lamb, which begins soon after birth, this interval in development was considered an excellent period to test the hypothesis that glucose perfusions could inhibit 2,3-DPG synthesis. Ten newborn lambs were divided into two groups and perfused either with glucose (15 mg/kg/min) or physiologic saline (45% NaCl) for 10 days. Blood gases, electrolytes, glycemia, O2 pressure at 50% Hb saturation, and 2,3-DPG levels were compared in the two groups. Glucose levels remained significantly elevated during the first 3 days in the glucose perfused group. The O2 pressure at 50% Hb saturation increased in both groups but was significantly lower in the glucose perfused group when determined on day 5 and 8. The postnatal increase in 2,3-DPG was significantly diminished in the glucose infused lambs, which suggests that glucose perfusion has an inhibiting effect on erythrocyte 2,3-DPG synthesis.

Relative rates of fetal hemoglobin and adult hemoglobin synthesis in cord blood of infants of insulin-dependent diabetic mothers.

Erythrocytosis, extramedullary erythropoiesis, and increased levels of plasma erythropoietin have been observed in newborn infants of diabetic mothers. Because there is evidence that there is a relationship between increased fetal hemoglobin production and acute erythropoietic expansion, it was considered important to study the proportion of fetal hemoglobin and adult hemoglobin synthesis in newborn infants of insulin-dependent diabetic mothers. Samples from nine newborn infants of diabetic mothers as well as nine control infants, ranging from 36 to 38 weeks of gestation, were incubated in an amino acid mixture containing [14C]leucine. The adult hemoglobin and fetal hemoglobin were then separated by column chromatography on DEAE [O-(diethylaminoethyl)] Sephadex. To confirm that the fetal hemoglobin obtained after Sephadex chromatography was not contaminated with other hemoglobins, several of the DEAE separations from each group were reconstituted and subjected to polypeptide chain elution using carboxyl-methyl cellulose chromatography. The data demonstrated that the newborn infants of diabetic mothers are synthesizing significantly more fetal hemoglobin than is expected for their period of development (82.2 +/- 3.6 v 72.8 +/- 4.2; P less than .005). It is suggested that the in utero environment of the fetus of the diabetic mother causes an increase in fetal hemoglobin synthesis.

Postnatal fetal and adult hemoglobin synthesis is preterm infants whose birth weight was less than 1,000 grams.

To determine if environmental factors could effect the switchover from fetal hemoglobin (HbF) to adult hemoglobin (HbA) synthesis, studies were carried out on blood samples from eight infants born at less than 1,000 g, when they had reached their postconceptional age corresponding to term. All of these infants required prolonged intensive care, multiple blood transfusions, and two required exchange transfusions. Several were ventilated mechanically for 60 d and two infants had bronchopulmonary dysplasia at the time of the study. The blood samples were incubated in an amino acid mixture containing [14C]leucine followed by column chromatography on DEAE Sephadex for separation of radioactive HbA and HbF. In spite of the extreme prematurity and poor growth of these sick infants, the proportional synthesis of HbF and HbA, as determined by the incorporation of [14C]leucine during the erythrocyte incubations, was characteristic of the period of human development from which the erythrocytes were obtained.

Oxygenation in anemic newborn lambs with high or low oxygen affinity red cells.

Experiments to determine the effect of the oxygen-hemoglobin dissociation curve on oxygen delivery during neonatal anemia, were carried out on 15 sedated and ventilated lambs less than 48 hr of age. Eight of the animals were exchange transfused with adult blood. The P50 of the exchange transfused group was 32.1 mm Hg (low O2 affinity) compared to 19.4 mm Hg for the controls (high O2 affinity). The animals were made anemic by isovolumic exchange transfusions with plasma. At different levels of hemoglobulin defined as mild (8 mg/100 ml), moderate (6 mg/100 ml), and severe (4 mg/100 ml) anemia, tissue oxygenation, hemodynamic status, and blood gases were compared. Mixed venous PO2 was significantly lower in the high affinity group throughout this study. Cardiac output was significantly greater in the low affinity group during severe anemia. Oxygen consumption remained stable in the low affinity group, but decreased significantly in the high affinity group when the anemia was severe. The data indicate that during severe anemia, blood with a high P50 is more capable of adequately oxygenating tissues than that with a low P50.

Synthesis, opiate receptor affinity, and conformational parameters of [4-tryptophan]enkephalin analogues.

A series of analogues of the opioid peptide enkephalin with tryptophan substituted for phenylalanine in position 4 was synthesized by the solid-phase method. The [Trp4]enkephalin analogues and the corresponding [Phe4]enkephalin analogues displayed nearly parallel affinities in the opiate receptor binding assay throughout the series. In a conformational study fluorescence parameters were measured and intramolecular Tyr-Trp distances were estimated on the basis of resonance energy transfer experiments. No gross conformational differences were observed between analogues with widely differing opiate receptor affinity; however, small but significant changes in the intramolecular distance between the phenol ring and the indole moiety and/or in their relative orientation became apparent in some compounds. Identical intramolecular distances of 9.3 +/- 0.2 angstrom between the two aromatic rings were obtained with [Trp4,Met5]enkephalin, [Trp4,Leu5]enkephalin, and the N-terminal tetrapeptide comprised in the latter two analogues, indicating the existence of folded conformationas in 2 X 10(-5) M aqueous solution and demonstrating conformational analogy between these three peptides. The conformational parameters are discussed in relation to the observed affinities and the putative opiate receptor topography.