The intrapulmonary arterial pattern in normal infancy and in transposition of the great arteries

Pulmonary Hypertension: The Hidden Danger for Newborns

Despite growing awareness of the clinical importance of pulmonary hypertension (PH) in preterm infants, uncertainty persists regarding the different clinical settings in which abnormalities of pulmonary vascular growth, function, and structure contribute to high morbidity and mortality, and potential interventions to improve outcomes are uncertain. A major gap for improving outcomes of preterm infants with PH has been the limited characterization of the distinct settings of PH and related disease-specific mechanisms in preterm infants that represent diverse pulmonary vascular phenotypes of prematurity. In comparison with term newborns, preterm infants have a higher risk for developing hypoxemia due to suprasystemic levels of PH in preterm infants shortly after birth or persistent pulmonary hypertension of the newborn (PPHN). Variable and milder levels of PH have also been demonstrated in preterm infants without evidence of severe hypoxemic respiratory failure, suggesting delayed vascular transition of the lung which is associated with higher risks of mortality and developing bronchopulmonary dysplasia (BPD). In addition, early echocardiographic signs of PH at day 7 are strongly associated with the subsequent diagnosis of BPD, late PH, and respiratory disease throughout early childhood. In infants with evolving or established BPD, PH that persists beyond the first few months of life in preterm infants is associated with high mortality. Recent data further show that PVD can persist and cause PH in prematurely born adults. Overall, more precise characterization and studies of diverse pulmonary vascular phenotypes in preterm infants will be likely to improve the development of therapeutic strategies to optimize care of preterm infants with PH.

Maternal adiposity--a determinant of perinatal and offspring outcomes?

Experimental and animal data suggest that maternal obesity during pregnancy adversely affects offspring health in the short-term and the long-term. Whether these effects occur in humans and influence population health is less clear. This Review explores evidence from intervention studies and observational studies that have used designs (such as family-based comparisons and Mendelian randomization) that might help improve understanding of the causal effects of maternal obesity in humans. Collectively, human studies provide evidence that maternal overweight and obesity is causally related to pregnancy complications, increased offspring weight and adiposity at birth, and the difficulties associated with delivery of large-for-gestational-age infants. The underlying mechanisms for these effects probably involve maternal and fetal dysregulation of glucose, insulin, lipid and amino acid metabolism. Some evidence exists that extreme maternal obesity (BMI ≥40 kg/m(2)) is causally related to a long-term increase in offspring adiposity, but further exploration of this relationship is needed. High gestational weight gain may result in a long-term increase in offspring adiposity if women are already overweight or have obesity at the start of pregnancy. To date, little high-quality human evidence exists that any of these effects are mediated by epigenetic mechanisms, but approaches to appropriately test this possibility are being developed.

The origins and roles of cholesterol and fatty acids in the fetus

The fetus grows at a rate that is unparalleled by that at any other stage of life. Significant amounts of cholesterol and fatty acids are required to maintain membrane growth. Recent studies have shown that these lipids are also necessary mediators of processes that are essential for proper development.

Arachidonic acid metabolic pathway of the rabbit placenta

Placenta microsomes prepared from animals late in gestation (29 days) efficiently metabolize arachidonic acid into PGE2, PGF2 alpha, PGD2, TxA2 and little or no prostacyclin. In contrast to the late gestation placenta, the early (17 day) placental microsomes synthesize primarily PGE2. The cytosolic (100,000 X g supernatant) fraction from early or late gestation placentae converted arachidonic acid, with a calcium dependent enzyme, into non-polar metabolites whose synthesis was inhibited by ETYA but not indomethacin. These metabolites were purified by HPLC and GC-MS analysis indicated the presence of 12-hydroxy-, 15-hydroxy-, and 11-hydroxy-eicosatetraenoic acid. The mitochondrial (8,000 X g pellet) produced PGE2; PGF2 alpha; 12-, 11-, 15-HETE; the C-17 fragment HHT; and the unusual cyclooxygenase metabolite 15-keto-PGE2. These biologically active metabolites may play a vital role in the reproductive function of the placenta.

Fatty acid utilization in perinatal de novo synthesis of tissues

The fatty acid content of fetal tissues was utilized to estimate essential fatty acid accretion during intrauterine growth. These rates of essential fatty acid accretion were used to predict that 400 mg/kg of body weight for omega-6 fatty acids and 50 mg/kg of body weight for omega-3 fatty acids per day would be used for intrauterine de novo synthesis of tissues. For the high risk low birth weight infant of approx. 1300 g birthweight it can be calculated that extrauterine de novo tissue synthesis would utilize about 280 mg/kg of body weight for omega-6 fatty acids and about 35 mg/kg of body weight for omega-3 fatty acids based on projected growth rates that are similar in composition to intrauterine growth and amount to 17 g of gain per day. From fatty acid analysis of brown and white adipose tissue it was estimated that some 70 and 78% of these net whole body accretion rates for essential fatty acids represent omega-6 and omega-3 fatty acid accretion in the adipose organs. Fatty acid analysis of human milk at day 16 of lactation was utilized to estimate the low birth weight infants' daily intake of major essential and other fatty acids. For intake levels of 120 kcal/kg it was concluded that the essential fatty acid content of mothers' own milk provides 6650 +/- 345 mg of total fatty acids, 850 +/- 160 mg of omega-6 fatty acids and 140 +/- 17 mg of omega-3 fatty acids.

The development of pulmonary vascular obstructive disease after successful Mustard operation in early infancy

Pulmonary vascular obstructive disease developed postoperatively in an infant with aortopulmonary transposition and intact ventricular septum who underwent a Mustard operation in 3 months of age. Preoperative catheterization had shown normal pulmonary artery pressures. Four months after surgery, catheterization showed pulmonary artery systolic pressure above the systemic level and a tortuous, attenuated pulmonary vascular tree visualized angiographically. Early corrective surgery may not preclude the development of pulmonary vascular obstructive disease in patients with aortopulmonary transposition.

Regulation of placental enzymes of the carbohydrate and lipid metabolic pathways

The activity of enzymes with a regulatory function in the pathways of glycolysis, gluconeogenesis, NADPH generation and fatty acid synthesis was measured in the placenta and liver of rats. Compared with the liver, a high activity of pyruvate kinase was found in the placenta, indicating a high glycolytic potential; a small capacity for gluconeogenesis was also present and a moderate to low activity of enzymes associated with lipogenesis. The activity of all placental enzymes fell from day 15 to 20 of gestation irrespective of the pathway they represented. The pattern of decline continued when the gestation was prolonged up to day 26 by the administration of chorionic gonadotropin. The rates of activity disappearance over 11 days of gestation differed for each enzyme, with half-lives ranging from 2.7 days for NADP-malate dehydrogenase to 7 days for glucose-6-phosphate dehydrogenase. In contrast, the activity of hepatic enzymes either remained unchanged or showed individual adaptation to the advancing pregnancy. The regression in placental metabolic capacity after day 15 of gestation was also evident by the decrease in glucose uptake and its channelling to lactate, CO2, glycerol and fatty acids. In addition, placental ageing was associated with triglyceride accumulation, mainly due to the decrease in free fatty acid oxidation. Treatment of pregnant rats with several hormones, while markedly affecting the hepatic enzyme activities, failed to induce appreciable changes in the corresponding placental enzymes. This was illustrated in the case of triiodothyronine treatment. Similarly, insulin deficiency induced by streptozotocin failed to elicit adaptive changes in placental enzyme activities typical of diabetes like those occurring in the maternal liver; some converse responses in the placenta were attributed to hyperglycaemia. On the other hand, responses in some fetal liver enzymes were suggestive of fetal hyperinsulinaemia. These observations indicate that placental enzymes are not susceptible to endocrine regulation and imply that placental metabolism is largely independent of the physiopathological alterations affecting the maternal organism. The gradual activity decreases with gestation suggest that the enzyme complement of the placenta, once developed, is designed to last through its limited lifespan without continuous replenishment. Within this context, no mechanism seems to operate to ind1ce the adaptive synthesis of individual enzymes, and the age of the placenta appears to be the primary factor determining its enzyme activity and metabolic performance.

Carbohydrate-induced lipogenesis in the human placenta of normal and diabetic pregnancies

Using in vitro incubation, human placental slices have been shown to synthesize lipid from 14-C fructose, but to a lesser extent than from 14-C glucose. Diabetic placentae did not incorporate more of either sugar into lipid than did placentae from normal pregnancies; nor did insulin in the incubation medium enhance lipogenesis. There was a correlation between the extent of incorporation of 14-C fructose and 14-C glucose into triglyceride, suggesting a linked enzyme system for phosphorylation of the two hexoses.