Supplemental protein and postnatal growth of very low birth weight infants: a randomized trial

BACKGROUND

Providing adequate nutritional support to promote optimal postnatal growth for very low birth weight (VLBW) infants has been a difficult problem to surmount in the NICU. During the past 4 decades, improvements in neonatal critical care have made it possible for more VLBW infants to survive to discharge from NICUs. The NICHD Neonatal Network reported that while intrauterine growth restriction was present in 22% of VLBW infants at birth, 91% demonstrated postnatal growth restriction by 36 weeks post menstrual age. The persistence of this nearly universal growth deficit is associated with the inadequacy of protein and energy intake, which may account for 45-50% of the postnatal growth restriction.

OBJECTIVE

The purpose of this study was to assess whether increasing enteral intake, using supplemental protein, would improve postnatal growth for VLBW infants.

STUDY DESIGN

Randomized clinical trial. Sixty-four infants were enrolled (34 in control group with 15 infants <1000 g, and 30 in intervention group with 13 infants <1000 g).

RESULT

There were no sustained statistical differences between weekly measurements of weight, length, head circumference, and skinfold thickness between groups. There were no significant differences between laboratory results except blood urea nitrogen at time of peak protein intake for intervention group.

CONCLUSIONS

Supplemental enteral protein had minimal to no effect on postnatal weight, length, head circumference, body mass, or length of stay. It may be most important to provide consistent sustained nutritional support with protein from birth to reduce postnatal growth restriction, especially for those infants <1000 g at birth.

Cellular distribution of insulin-like growth factor binding protein mRNAs and peptides during rat lung development

A role for IGF binding proteins (IGFBPs) in lung development is suggested by the identification of IGFBPs in lung tissue and production of IGFBPs by fetal lung cells in culture. To characterize the expression of IGFBPs during lung development in the rat in vivo (16 days gestation through adulthood), the expression of IGFBP mRNAs (IGFBP-1 to IGFBP-6) was examined by Northern analysis and in situ hybridization, and IGFBP peptides (IGFBP-2, IGFBP-3, and IGFBP-5) were localized by immunohistochemistry. IGFBP-1 mRNA was not detectable. IGFBP-2 mRNA (1.8 kb) was expressed in both fetal and postnatal life with peak expression during the fetal pseudoglandular stage. IGFBP-2 mRNA was localized mainly to airway epithelium. IGFBP-3 mRNA (2.4 kb) was maximally expressed postnatally in the saccular stage of lung development; it was identified in airway epithelium and interstitium in the fetal lung, but predominantly in airway epithelium after birth. IGFBP-4 (2.6 kb) and IGFBP-5 (6.0 kb) mRNA levels were maximal after birth, from 3 to 21 days postnatal (saccular and alveolar stage). IGFBP-4 mRNA was localized primarily to the interstitium and blood vessels early in development, but was abundant in airway epithelium in the adult. IGFBP-5 mRNA was most abundant in the airway epithelium. IGFBP-3, IGFBP-4, IGFBP-5, and to a lesser extent IGFBP-6 were localized to the large cartilaginous airways in the adult. IGFBP-2, IGFBP-3, and IGFBP-5 peptides were distributed more widely than their respective mRNAs, with a temporal pattern of immunoreactivity following that of their mRNAs. Maximal staining was noted in airway epithelium for IGFBP-2 in the newborn, for IGFBP-3 in the saccular stage (newborn to 3 days postnatal), and for IGFBP-5 in the alveolar stage (5 to 21 days postnatal). Our studies demonstrate that IGFBP-2, IGFBP-3, IGFBP-4, and IGFBP-5 are synthesized and distributed in spatially and temporally different patterns in the developing lung. The widespread distribution of IGFBP immunoreactivity compared with their respective mRNAs suggests that IGFBPs are important paracrine factors in the regulation of IGF action in the developing lung.

Effects of mechanical factors on growth and maturation of the lung in fetal sheep

Previous fetal studies indicated that endocrine factors control surfactant maturation, whereas mechanical forces affect lung growth, but not surfactant. We altered mechanical forces in fetal sheep lungs at 100-108 days gestation by tracheal ligation (TL, n = 15, 7 successful studies) to accelerate lung growth, transection of cervical spinal cord (TCSC, n = 17, 6 successful studies) to produce lung hypoplasia, or sham operation (n = 11, 6 successful studies). The reasons for the high mortality rates are not known. At delivery (130-142 days), groups were similar in gestational age, weight, and cortisol. Effects on lung growth were similar to, but effects on surfactant differed from, previous reports. TL increased lung growth but decreased saturated phosphatidylcholine (SatPC) and surfactant protein (SP)A and apparently decreased SP-B and relative numbers of alveolar type II cells (based on immunohistochemical studies of 1 animal in each group); TCSC had opposite effects. In contrast to a previous study (J. A. Kitterman, G. C. Liggins, G. A. Campos, J. A. Clements, C. S. Forster, C. H. Lee, and R. K. Creasy, J. Appl. Physiol, 51: 384-390, 1981), SatPC did not correlate with cortisol. We conclude that altering mechanical forces in fetal lung affects not only lung growth but also surfactant maturation and possibly alveolar epithelial differentiation and disturbs the normal correlation between cortisol and surfactant. Associated changes in insulin-like growth factor I (IGF-I; increased by TL, P = 0.003) suggest a possible role for IGF-I in these effects.

Spatial and temporal distribution of insulin-like growth factors I and II during development of rat lung

Insulin-like growth factors (IGF) I and II genes are expressed in developing lung tissue, but the details of distribution during different stages of lung development have not been delineated. To define the role of IGFs in lung development, the expression of IGF-I and IGF-II mRNAs and peptides was examined in rat lungs from 16-day gestation through adulthood. The expression of stable IGF mRNAs was investigated by Northern analysis, IGF mRNAs were localized by in situ hybridization histochemistry, and IGF peptides were localized by immunohistochemistry. Four IGF-II transcripts (3.5, 2.2, 1.8, and 1.0 kb) were identified; IGF-II mRNA levels were highest early in fetal life (day 16-18) and decreased gradually until 28 days postnatal. Four IGF-I transcripts (7.8, 4.4, 2.1, and 0.6 kb) were detected but were of low abundance. IGF-II mRNA was localized mainly in mesenchymal cells but was also identified in the airway epithelium, with peak expression in the perinatal lung. IGF-II peptide was prominent in late fetal life and for 5 days after birth and was identified in both mesenchymal and epithelial cells. In contrast, there was little evidence of IGF-I mRNA and peptide until after birth: IGF-I was most easily identified between 5 and 14 days postnatal (the height of alveolar multiplication and formation), when both mRNA and peptide were localized to mesenchymal and epithelial cells. Our studies demonstrate that IGF-I and IGF-II are synthesized and distributed in spatially and temporally different patterns in the developing lung. IGF-I and IGF-II peptides are more widely identified than their respective mRNAs, suggesting a paracrine distribution in the developing lung.

Fetal lung growth. Influence of pulmonary arterial flow and surgery in sheep

Aberrant pulmonary arterial flow has been associated with pulmonary hypoplasia, which is a common cause of death in newborns. The current experiments were designed to confirm whether interruption of postductal main pulmonary artery (MPA) flow causes pulmonary hypoplasia. In addition, the effect of fetal surgery on lung growth was investigated. Fetal sheep, instrumented at 107 to 115 d gestation (MPA ligated [n = 5], sham operated [n = 3], and monitored [no thoracotomy, n = 5]), and unoperated twin fetuses (140-d controls, n = 5) were used for analysis of lung growth at 136 to 140 d gestation. Morphometric measurement of lung tissue volumes and assays of DNA, protein, and saturated phosphatidylcholine (SPC) were used to assess lung growth. MPA ligation significantly decreased lung growth and maturation as indicated by decreased surface area and volumes of fine nonparenchyma, future airspace, and parenchymal tissue, and by decreased lung weights, total DNA, protein, and SPC content. There was a significant increase in the volume percentage of coarse nonparenchyma and a decrease in the volume percentage of future airspace. The pattern of lung growth after MPA ligation suggests that growth of peripheral airspace and parenchymal tissue components does not occur, resulting in a significant decrease in the amount of new tissue formed and delayed tissue maturation. Fetal surgery significantly changed only DNA, protein, and SPC content. Studies of the regulation of lung growth must consider the role of pulmonary arterial flow and the smaller, but significant effects of fetal surgery.

Main pulmonary artery ligation reduces lung fluid production in fetal sheep

Pulmonary hypoplasia is increasing as a cause of neonatal death. To understand the pathophysiology of pulmonary hypoplasia, the physiology of fetal lung growth must first be understood. Lung fluid production and fetal breathing are primary factors regulating lung growth. Interruption of pulmonary arterial flow also decreases fetal lung growth. To define the relationship of pulmonary arterial flow to other factors known to be important for fetal lung growth, breathing and lung fluid production were measured after postductal main pulmonary artery (MPA) ligation in fetal sheep. Surgical preparation at 107-116 d gestation included placement of vascular catheters and a tracheal catheter connected to an intrauterine collection bag for lung fluid. Five fetuses served as monitored controls (catheters only), 3 as sham operated controls (catheters and thoracotomy), and 7 had MPA ligation. MPA ligation significantly decreased lung weights at 131-140 d; mean dry weight (g): MPA ligation--6.7, sham--23.4, monitored--22.3. Mean rates of lung fluid production (mL/h) were also decreased (d gestation): 116-122 d: MPA ligation--2.2, sham--9.1, monitored--6.8; 123-129 d: MPA ligation--2.1, sham--9.1, monitored--6.2; 130-136 d: MPA ligation--1.5, sham--12.4, monitored--7.7. There were no differences between MPA ligated, sham, and monitored fetuses in the incidence or intensity of fetal breathing movements. Decreased lung fluid production after main pulmonary artery ligation is most likely due to decreased secretion of lung fluid. Pulmonary arterial flow in other models of pulmonary hypoplasia which decrease lung fluid production (i.e., oligohydramnios) should also be examined.

Morphometric study of the role of pulmonary arterial flow in fetal lung growth in sheep

Pulmonary hypoplasia has been associated with absent or hypoplastic pulmonary artery in four cases in humans. Despite these reports, the effects of decreased pulmonary arterial flow on fetal lung growth have not been adequately studied. This study defines the effects of left pulmonary artery (LPA) ligation on fetal lung growth in sheep by comparing morphometrically determined pulmonary volumes from LPA-ligated, sham-operated, and un-operated control fetuses. LPA ligation (n = 5) or sham operation (n = 4) was performed at 105- to 114-d gestation. lungs were intratracheally fixed for light microscopy. At 112 d (n = 4) and at 140 d (n = 4), unoperated control fetuses were similarly delivered. Absolute pulmonary volumes were then measured using standard stereologic methods. Normal growth of the left lung from 112 to 140 d resulted in significant increases in wet and dry wt, displacement volume, and volumes of future airspace and capillary contents. LPA ligation caused significant decreases in left lung wet and dry wt, displacement volume, and in absolute volumes of fine nonparenchymal, future airspace, parenchymal tissue, and capillary contents compared to sham-operated and 140-d controls. Parenchymal tissue volume was also less than in 112-d controls. In addition, lung wt, displacement volume, and future airspace volume were significantly decreased in sham-operated fetuses compared to 140-d controls. The effects of LPA ligation on bronchial collateral circulation and factors known to affect lung growth (i.e. lung fluid volume) remain to be determined. Clearly, during the canalicular and alveolar stage of fetal lung development, pulmonary arterial flow is necessary for normal lung growth.

Meclofenamate does not affect lung development in fetal sheep

Prostaglandins may be involved in some aspects of fetal lung development, including surfactant metabolism, tracheal fluid production, and possibly lung growth. In the fetus, during the days before delivery, plasma PGE2 concentration increases and concurrently, tracheal fluid production decreases and surfactant production increases. To determine whether the increase in PGE2, specifically plasma PGE2 concentration, is responsible for these changes, we continuously infused the prostaglandin synthetase inhibitor, meclofenamate (0.7 mg/h per kg), into 8 fetal sheep for 5-13 days before delivery; 5 control fetuses received a continuous infusion of solvent for 5-11 days before delivery. Meclofenamate infusion significantly decreased plasma PGE2 concentrations until the day of delivery. However, meclofenamate did not affect tracheal fluid production or its decrease before delivery, fetal plasma cortisol concentration, surfactant content of tracheal fluid and lung tissue, organ weights, lung weights, or lung DNA and protein content. We conclude that the changes in lung development during the days before delivery are not dependent on the usual high fetal plasma concentration of PGE2 or its increase before delivery.

Prostaglandin E2 causes hypoventilation and apnea in newborn lambs

To test the hypothesis that prostaglandin (PG) E2 is a respiratory depressant in the newborn lamb, 12 chronically catheterized, unanesthetized lambs (age 2-6 days) were infused with progressively increasing doses of PGE2 (0.1, 0.5, 1.0, and 5.0 micrograms.kg-1.min-1; 30 min for each dose) into the ascending aorta. PGE2 caused significant progressive decreases in ventilation (due to decreased tidal volume and breathing rate), heart rate, blood pressure, and percent of the time spent in low-voltage electrocortical activity (LVA). PGE2 also caused respiratory acidosis, hypoxemia, and increased frequency and duration of apneic events (greater than 3 s). During the infusion there was a dose-related increase in plasma concentration of PGE2. At 30 min postinfusion, all measured variables showed recovery, although arterial pH, CO2 tension, and plasma PGE2 remained significantly different from control values, and the percent time in LVA was even higher than during control. Infusion of the vehicle alone (n = 5) caused no significant changes in any of the measured variables. The results, taken in combination with previous fetal studies, indicate that PGE2 has marked inhibitory effects on breathing movements both before and after birth.

Effects of meclofenamate on breathing movements in fetal sheep before delivery

There is evidence that prostaglandins (PG), specifically PGE2, participate in the regulation of fetal breathing movements (FBM). During late gestation, when FBM occur intermittently and primarily during low-voltage electrocortical activity, the concentration of PGE2 in fetal plasma ([PGE2]) is high. During the days before delivery [PGE2] increases and FBM decrease. To determine whether the increase in [PGE2] is responsible for the concurrent decrease in FBM, we infused the prostaglandin synthase inhibitor, meclofenamate (0.7 mg.kg-1.h-1), into eight fetal sheep continuously for 5-13 days before delivery; five control fetuses received a continuous infusion of the solvent for 5-11 days before delivery. Compared with control infusion, meclofenamate caused a significant decrease in [PGE 2] until the day of delivery and a significant increase in FBM [overall and during high-voltage electrocortical activity (HVA)] until 2 days before delivery. Although there were significant correlations between [PGE2] and FBM (overall and during HVA), both groups showed similar decreases in FBM during the 2 days before delivery. We conclude that the decrease in FBM before delivery is not dependent on the concurrent increase in [PGE2].

Effects of prostaglandins on fetal breathing do not involve peripheral chemoreceptors

In sheep, prostaglandin (PG) E2 inhibits fetal breathing movements and meclofenamate, a PG synthetase inhibitor, causes a marked stimulation of fetal breathing movements; the site of action of these agents is not known. To determine whether these effects are mediated through the peripheral chemoreceptors, we studied 13 fetal sheep at gestational ages of 127 to 138 days. Seven fetuses had bilateral section of the carotid sinus and vagus nerves (denervated); six had sham operations. Beginning at least 6 days after the operation, we infused PGE2 (0.6 microgram X kg-1 X min-1) into five denervated and five sham-operated fetuses and meclofenamate (0.4 mg X kg-1 X h-1) into six denervated and four sham-operated fetuses. Infusions averaged 20 h in duration. During preinfusion control periods, the incidence of fetal breathing movements (% of time) was lower in denervated than in sham-operated fetuses (18.9% vs. 31.5%; P less than 0.005). In both groups, the incidence of fetal breathing movements was decreased by PGE2 and was increased by meclofenamate; when expressed as absolute values, the magnitude of the changes with both agents was greater in sham-operated fetuses than denervated fetuses. However, the effects were similar in both groups when the changes were expressed as a percent of the respective control values. The incidence of fetal breathing movements (% of control) was decreased by PGE2 to 25.4% in denervated and to 28.2% in sham-operated fetuses and was increased by meclofenamate to 297.3% in denervated and to 304.0% in sham-operated fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of breathing movements in fetal sheep by prostaglandin E2

In fetal sheep, plasma prostaglandin (PG) E2 concentrations are high, and fetal breathing movements (FBM) occur intermittently, primarily during low-voltage fast electrocortical activity (LVFA). There is evidence suggesting that prostaglandins, specifically PGE2, may regulate FBM. To define the physiological role of PGE2 in regulation of FBM, we infused meclofenamate (0.9 mg X kg-1 X h-1), a prostaglandin synthetase inhibitor, into six fetal sheep to suppress endogenous prostaglandin production. Afterward, PGE2 was added in mean doses of 9, 18, 36, and 90 ng X kg-1 X min-1. Meclofenamate decreased PGE2 concentrations and increased FBM, especially during high-voltage slow electrocortical activity (HVSA). Addition of PGE2 reversed the effects of meclofenamate, increasing PGE2 concentrations and decreasing FBM, especially during HVSA. The response to PGE2 was dose dependent; the overall incidence of FBM and incidences of FBM during HVSA and LVFA were inversely correlated with both the infused PGE2 dose and the mean PGE2 concentration. At higher doses of PGE2, FBM occurred intermittently and only during LVFA; thus PGE2 infusion restored the physiological pattern of FBM. These results indicate that PGE2 regulates FBM by inhibiting FBM during HVSA.

Denervation of peripheral chemoreceptors decreases breathing movements in fetal sheep

The role of the peripheral chemoreceptors in the control of fetal breathing movements has not been fully defined. To determine whether denervation of the peripheral chemoreceptors affects fetal breathing movements, we studied 14 chronically catheterized fetal sheep from 120 to 138 days of gestation. In seven fetuses the chemoreceptors were denervated by bilateral section of the vagus and carotid sinus nerves; in seven others, sham operations were performed. We compared several variables during two study periods: 0-5 and 6-13 days after operation. In the denervated fetuses there were significant decreases in the incidence and amplitude of fetal breathing movements during both study periods. There were no differences between the two groups in incidence of low-voltage electrocortical activity, arterial pH and blood gas tensions, fetal heart rate, mean arterial blood pressure, or duration of survival after operation or birth weight. We conclude that denervation of the peripheral chemoreceptors decreases fetal breathing movements. These results indicate that the peripheral chemoreceptors are active during fetal life and participate in the control of fetal breathing movements.