Ian Gross

INHALED NITRIC OXIDE AND PERSISTENT PULMONARY HYPERTENSION OF THE NEWBORN

Background Persistent pulmonary hypertension of the newborn causes systemic arterial hypoxemia because of increased pulmonary vascular resistance and right-to-left shunting of deoxygenated blood. Inhaled nitric oxide decreases pulmonary vascular resistance in newborns. We studied whether inhaled nitric oxide decreases severe hypoxemia in infants with persistent pulmonary hypertension. Methods In a prospective, multicenter study, 58 full-term infants with severe hypoxemia and persistent pulmonary hypertension were randomly assigned to breathe either a control gas (nitrogen) or nitric oxide (80 parts per million), mixed with oxygen from a ventilator. If oxygenation increased after 20 minutes and systemic blood pressure did not decrease, the treatment was considered successful and was continued at lower concentrations. Otherwise, it was discontinued and alternative therapies, including extracorporeal membrane oxygenation, were used. Results Inhaled nitric oxide successfully doubled systemic oxygenation in 16 of 30 infants (53 percent), whereas conventional therapy without inhaled nitric oxide increased oxygenation in only 2 of 28 infants (7 percent). Long-term therapy with inhaled nitric oxide sustained systemic oxygenation in 75 percent of the infants who had initial improvement. Extracorporeal membrane oxygenation was required in 71 percent of the control group and 40 percent of the nitric oxide group (P=0.02). The number of deaths was similar in the two groups. Inhaled nitric oxide did not cause systemic hypotension or increase methemoglobin levels. Conclusions Inhaled nitric oxide improves systemic oxygenation in infants with persistent pulmonary hypertension and may reduce the need for more invasive treatments.

Development of glycogen and phospholipid metabolism in fetal and newborn rat lung

Glucose, a major metabolic substrate for the mammalian fetus, probably makes significant contributions to surface active phospholipid synthesis in adult lung. We examined the developmental patterns of glycogen content, glycogen synthase activity, glycogen phosphorylase activity and glucose oxidation in fetal and newborn rat lung. These patterns were correlated with the development of phosphatidylcholine synthesis, content and the activities of enzymes involved in phosphatidylcholine synthesis. Fetal lung glycogen concentration increased until day 20 of gestation (term is 22 days) after which it declined to low levels. Activity of both glycogen synthase I and total glycogen synthase (I + D) in fetal lung increased late in gestation. Increased lung glycogen concentration preceded changes in enzyme activity. Glycogen phosphorylase a and total glycogen phosphorylase (a + b) activity in fetal lung increased during the period of prenatal glycogen depletion. The activity of the pentose phosphate pathway, as measured by the ratio of CO2 derived from oxidation of C1 and C6 of glucose, declined after birth. Fetal lung total phospholipid, phosphatidycholine and disaturated phosphatidylcholine content increased by 60, 90 and 180%, respectively, between day 19 of gestation and the first postnatal day. Incorporation of choline into phosphatidylcholine and disaturated phosphatidylcholine increased 10-fold during this time. No changes in phosphatidylcholine enzyme activities were noted during gestation, but both choline phosphate cytidylyltransferase and phosphatidate phosphatase activity increased after birth. The possible contributions of carbohydrate derived from fetal lung glycogen to phospholipid synthesis are discussed.

A Comparison of Early-Onset Group B Streptococcal Neonatal Infection and the Respiratory-Distress Syndrome of the Newborn

In attempting to differentiate early-onset Group B streptococcal infection from hyaline-membrane disease we found features of severe Group B infection to be rupture of the membranes for more than 12 hours before delivery (four or eight versus one of nine), gram-positive cocci in the gastric aspirate (four or four versus none of one), apnea and shock in the first 24 hours of life (seven of eight versus none of nine), and the generation of lower peak inspiratory pressures on avolume-cycled respirator (mean of 36.5 +/- 2.8 versus 63.9 +/- 6.2 cm of water; P = 0.005). In eight fatal cases of Group B infection, four patients had radiographic features indistinguishable from hyaline-membrane disease whereas the other cases were consistent with neonatal pneumonia. Seven of the eight infected infants had no histologic evidence of coexisting hyaline-membrane disease. Microscopical features of Group B infection included cocci in unevenly distributed hyaline membranes and minimal atelectasis. Group B streptococcal infection differs clinically and pathologically from hyaline-membrane disease. Differentiating clinical features include early apnea and shock and lower inspiratory pressures on mechanical ventilation.

Effects of betamethasone on phospholipid content, composition and biosynthesis in the fetal rabbit lung.

Administration of betamethasone (0.2 mg/kg, intramuscularly) to pregnant rabbits had the following effects on the fetal lung at 26--27 days gestation. It increased the amount of phosphatidylcholine in lung lavage by 70% and almost doubled the phosphatidylcholine/sphingomyelin ratio, it increased the rate of incorporation of choline into phosphatidylcholine in fetal lung slices by up to 90%, it increased the activities of pulmonary cholinephosphate cytidylyltransferase and phosphatidate phosphatase by 50% and it reduced the amount of lung glycogen to 60% of the amount in the controls. Betamethasone had no effect on the activities of pulmonary cholinephosphotransferase or lysolecithin: lysolecithin acyltransferase but it slightly decreased the activity of choline kinase. Betamethasone administration to the doe did not increase the amount of surfactant phospholipid in fetal lung lavage to as great an extent as did direct administration of cortisol to the fetuses. Neither did betamethasone stimulate the activity of pulmonary cholinephosphotransferase. These data suggest that agents other than glucocorticoids mediate the stress-induced acceleration of fetal lung maturation and surfactant production.

The influence of hormones on the biochemical development of fetal rat lung in organ culture: I. Estrogen

Abstract It was recently demonstrated that 17β-estradiol enhances phosphatidylcholine synthesis in fetal lung in vivo. In order to determine whether estrogen acts directly on the lung, we examined the influence of 17β-estradiol on phospholipid and glycogen metabolism in explants of 18 day fetal rat lung in organ culture. Exposure of the explants to 17β-estradiol resulted in significant stimulation of [Me- 3 H]choline incorporation into phosphatidylcholine, disaturated phosphatidylcholine and sphingomyelin. Incorporation of [ 3 H]acetate into total phospholipid was increased by 63% ( P P 3 H] acetate in the various phospholipid fractions, it was found that there was a 29% increase in the phos-phatidylglycerol fraction ( P P P These data indicate that estrogen acts directly on the fetal lung and stimulates the incorporation of choline and acetate into phospholipids. It may specifically enhance incorporation into phosphatidylglycerol, the second most abundant phospholipid in pulmonary surfactant.

Influence of epidermal growth factor on fetal rat lung development in vitro.

ABSTRACT. Epidermal growth factor (EGF) has been shown to enhance cell multiplication or differentiation in a number of developing tissues. We have examined the effects of this growth factor on the biochemical development of explants of fetal rat lung, cultured in serum-free medium for 48 h. EGF enhanced the rate of choline incorporation into phosphatidylcholine and disaturated phosphatidylcholine in a dose dependent fashion. Half maximal stimulation occurred at a concentration of 1.0 nM, similar to the Kd for EGF binding to rat lung cell membranes. There was also significant stimulation of acetate incorporation into all phospholipids, particularly phosphatidylglycerol (539%), and increased distribution of radioactivity from acetate in this phospholipid fraction. Exposure to EGF stimulated PC synthesis in 18- and 19-day explants (term is 22 days) whereas maximal enhancement of DNA synthesis occurred after this time. This sequence differs from that observed during early embryonic development when EGF initially enhances cell multiplication. An additive interaction with regard to enhancement of PC synthesis was observed with EGF and thyroid hormone, but not EGF and dexamethasone. EGF had no effect on the activity of the enzymes of the choline incorporation pathway of phosphatidylcholine synthesis or on the activity of enzymes involved with acidic phospholipid synthesis. Fetal lung EGF content and EGF binding capacity were not increased by glucocorticoid treatment and similarly glucocorticoid binding capacity was not increased by EGF. These data indicate that EGF enhances fetal rat lung phospholipid synthesis in a dose-dependent manner and suggest that this is a direct effect on the lung tissue mediated by specific receptors.

Plasma Thyroid Hormones and Prolactin in Premature Infants and Their Mothers after Prenatal Treatment with Thyrotropin-Releasing Hormone

ABSTRACT: We assayed TSH, triiodothyronine, free thyroxine, and prolactin (PRL) in plasma of women and infants participating in a trial of prenatal thyrotropin-releasing hormone (TRH) treatment for prevention of newborn lung disease. Women in labor at 26–34 wk of gestation received 400 μg of TRH i.v. every 8 h (one to four doses) plus 12 mg betamethasone (one or two doses); controls received saline plus betamethasone. Mean cord concentrations in control infants were TSH 9.7 mU/L, triiodothyronine 0.6 nmol/L (40.2 ng/dL), free thyroxine 14.4 pmol/L (1.13 ng/dL), and PRL 67.6 μg/L. TRH increased maternal plasma TSH by 100% at 2–4 h after treatment and decreased levels by 28–34% at 5–36 h. In cord blood of treated infants delivered at 2–6 h, TSH, triiodothyronine, and PRL were all increased about 2-fold versus control, and free thyroxine was increased 19%; the response was similar after one, two, three, or four doses of TRH. In treated infants delivered at 13–36 h, cord TSH and triiodothyronine levels were decreased 62 and 54%, respectively, and all thyroid hormones were lower after birth at 2 h of age versus control. We conclude that prenatal TRH administration increases thyroid hormones and PRL in preterm fetuses to levels similar to those normally occurring at term. Pituitary-thyroid function is transiently suppressed after treatment to a greater extent in fetus than mother, and infants born during the early phase of suppression do not have the normal postnatal surge in thyroid hormones.

Thyrotropin-Releasing Hormone Increases the Amount of Surfactant in Lung Lavage from Fetal Rabbits

Summary: Administration of thyrotropin-releasing hormone (TRH) to pregnant rabbits at 25 and 26 days of gestation results in increased pulmonary surfactant production by the fetus at 27 days (full term is 31 days). There was 60% more total phospholipid and 150% more phosphatidylcholine (the major component of surfactant) in the lung lavage from the fetuses in the treated group than in that from the controls. Lung lavage from the fetuses in the treated litters contained 13.4 ± 1.6 μg of total phospholipid phosphorus/g lung dry wt and 5.6 ± 1.1 μg of phosphatidylcholine phosphorus while that from the fetuses in the control litters contained only 8.2 ± 1.1 μg and 2.2 ± 0.4 μg, respectively. The phosphatidylcholine/sphingomyelin ratio increased from 1.0 in the lavage from the controls to 2.2 in that from the treated group. These changes in lung lavage phospholipid content and composition are in the direction of increased lung maturation. TRH administration had no effect on the incorporation of choline into phosphatidylcholine in fetal lung slices. These data suggest that TRH stimulates surfactant release rather than synthesis.Speculation: TRH has a physiologic role in fetal lung maturation and surfactant production. It may potentially be used in the prevention of the respiratory distress syndrome in humans.

Glucocorticoid stimulation of choline-phosphate cytidylyltransferase activity in fetal rat lung: receptor-response relationships.

A number of previous studies using in vivo and cultured fetal lung models have shown that the activity of choline-phosphate cytidylyltransferase, the enzyme which catalyzes a rate-limiting reaction in de novo phosphatidylcholine synthesis, is increased by glucocorticoids and other hormones which accelerate fetal lung maturation. To examine the mechanism of this glucocorticoid action further, we examined the effect of dexamethasone on cytidylyltransferase activity in cultured fetal rat lung explants and related it to specific dexamethasone binding. Dexamethasone stimulated cytidylyltransferase activity in the homogenate, microsomal and 105,000 X g supernatant fractions. The hormone did not alter the subcellular distribution of the enzyme, however; the bulk of the activity was in the supernatant fraction in both the control and dexamethasone-treated cultures. The dose-response curves for stimulation of cytidylyltransferase activity in the supernatant fraction and specific nuclear binding of dexamethasone were similar and both plateaued at approx. 20 nM. The EC50 for cytidylyltransferase stimulation was 6.6 nM and the Kd for dexamethasone binding was 6.8 nM. The relative potencies of various steroids for stimulating choline-phosphate cytidylyltransferase and for specific nuclear glucocorticoid binding were the same: dexamethasone greater than cortisol = corticosterone = dihydrocorticosterone greater than progesterone. The stimulation by dexamethasone of cytidylyltransferase activity and of choline incorporation into phosphatidylcholine were both abolished by actinomycin D. These data show that the stimulatory effect of dexamethasone on fetal rat lung choline-phosphate cytidylyltransferase activity is largely on the enzyme in the supernatant fraction and does not involve enzyme translocation to the microsomes as has been reported for cytidylyltransferase activation in some other systems. This effect of dexamethasone is a receptor-mediated process dependent on RNA and protein synthesis.

The influence of hormones on the biochemical development of fetal rat lung in organ culture. II. Insulin.

Summary: The influence of insulin on the biochemical and morphologic maturation of 19-day fetal rat lung (term is 22 days) was studied in an organ culture system. Exposure to insulin for 24 hr resulted in a significant increase in the glycogen content and the rate of glucose oxidation to CO2. In association with this, there was morphologic evidence of delayed lung maturation as evidenced by a significant decrease in the number of lamellar bodies and type II cells in the explants.Insulin treatment had no effect on the rate of choline incorporation into phosphatidylcholine (PC) or disaturated PC and did not antagonize the dexamethasone-induced stimulation of choline incorporation into PC. When the incorporation of [3H]acetate into the various phospholipid fractions was examined, however, it was found that exposure to insulin resulted in a significant decrease in the percentage of phospholipid radioactivity in the disaturated PC fraction and an increase in the percentage of radioactivity in the “membrane” phospholipids, phosphatidylethanolamine, phosphatidylinositol plus phosphatidylserine, and sphingomyelin. There was no significant change in the unsaturated PC and phosphatidylglycerol fractions. Treatment with dexamethasone generally had the opposite effect to insulin with regard to acetate incorporation into the various phospholipid fractions, and when the two hormones were combined, this effect was diminished or abolished. The effects of insulin could not be accounted for on the basis of a change in activity of any of the enzymes of phospholipid synthesis that were examined.These findings suggest that insulin stimulates the synthesis of the cell membrane phospholipids while decreasing that of the surfactant phospholipid, disaturated PC.Speculation: Insulin stimulates lung cell growth while delaying lung cell differentiation.