ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The bone disease of preterm birth has traditionally been explained by a decrease in bone formation from insufficient availability of calcium and phosphorus. However, there is emerging evidence that there is increased bone resorption in the bone disease of preterm birth, an observation that indicates some other explanation for this condition. The biomechanical model of postnatal bone formation states that, through a regulatory feedback system in the bone called the mechanostat, bone is able to respond to increased bone loading by increasing bone strength and to decreased bone loading by decreasing bone strength. It is suggested that this increased bone resorption in the markedly preterm infant compared with the term infant is secondary to decreased bone loading. Application of this model to the fetus and preterm infant suggests that intrauterine bone loading of the fetus from movement and kicking against the uterus is critical for normal fetal bone formation. The associated muscle growth from this activity also contributes to bone loading. The markedly preterm infant is deprived of much of this critical time period of intrauterine bone accretion, and bone formation occurs in the less favorable extrauterine environment, where there is significantly less bone loading.

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The isolation of human fetal DNA from the maternal circulation has provided a source of fetal material for prenatal diagnosis. The objective of this study was to investigate whether a similar pattern could be observed in the maternal circulation of male-bearing gravid rhesus monkeys. A real-time PCR TaqMan system for the rhesus Y-chromosome sex determining region was used to determine fetal sex and to quantify fetal DNA concentrations. Results in 14 healthy pregnancies indicated that fetal male DNA could be routinely detected in maternal serum by 50 d of gestation (late first trimester; term 165 ± 10 d). Fetal DNA concentrations increased with advancing gestation, reaching a mean of 341 genome equivalents/mL of serum (range 11–1570 copies/mL) in the last trimester of gestation, similar to findings in humans. The fetal DNA concentration corresponded to 2.7% of the total maternal serum DNA in the third trimester. Similar to findings in humans, male fetal DNA sequences were not detected postpartum (through 4 wk postpartum) or in animals with a previous history of delivering male offspring. These data indicate that fetal male DNA is present in the maternal circulation of gravid rhesus monkeys comparable to findings in humans and further support the use of this nonhuman primate species as a model to investigate fetomaternal cell trafficking and microchimerism.

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Greater protein intakes are required than have been commonly used to achieve fetalin uteroprotein accretion rates in preterm neonates. To study the efficacy and safety of more aggressive amino acid intake, we performed a prospective randomized study in 28 infants [mean wt, 946 ± 40 g (SEM)] of 1 (low amino acid intake, LAA)versus3 g·kg−1·d−1(high amino acid intake, HAA) at 52.0 ± 3.0 h of life. After a minimum of 12 h of parenteral nutrition, efficacy was determined by protein balance and was significantly lower in the LAAversusHAA groups by both nitrogen balance (−0.26 ± 0.11versus1.16 ± 0.15 g·kg−1·d−1,p< 0.00005) and leucine stable isotope (0.184 ± 0.17versus1.63 ± 0.20 g·kg−1·d−1,p< 0.0005) methods. Leucine flux and oxidation and nonoxidative leucine disposal rates were all significantly higher in the HAAversusLAA groups (249 ± 13versus164 ± 8, 69 ± 5versus32 ± 3, and 180 ± 10versus132 ± 8 &mgr;mol·kg−1·h−1, respectively,p< 0.005), but leucine appearance from protein breakdown was not (140 ± 15 in HAAversus128 ± 8 &mgr;mol·kg−1·h−1). In terms of possible toxicity with HAA, there were no significant differences between groups in the amount of sodium bicarbonate administered, degree of acidosis as determined by base deficit, or blood urea nitrogen concentration. Parenteral HAAversusLAA intake resulted in increased protein accretion, primarily by increasing protein synthesisversussuppressing protein breakdown, and appeared to be well tolerated by very preterm infants in the first days of life.

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Bone elongation in the postnatal animal is a result of cellular activity during endochondral ossification. Growth plate chondrocytes undergo a differentiation cascade involving stem cell clonal expansion and cellular enlargement during hypertrophy. Nutritional status has a significant effect on rates of bone growth, and a period of accelerated growth will occur if nutritional stunting of growth in early childhood can be corrected. This study focuses on changes inratesof increase in bone length in a model of catch-up growth in 4-wk-old male rats. Animals fasted for 3 d reached a weight ∼60% of the control littermates. By 28 d postfasting, fasted animals had regained weight to 95% of control levels. A 3-d fast caused an immediate and profound decrease in rate of growth in the proximal tibial growth plate to only 30% of that of control animals, whilestoppinggrowth in the distal tibial growth plate. During the rapid initial rate acceleration of bone elongation, growth rate in both growth plates reached that of the control littermates by 7 d postfasting. The proximal tibial growth plate then maintained rates that were 10–15% higher than control over the rest of the experimental period. By 10 d postfasting, the previously fasted animals were on the same weight/rate trajectory as the control littermates. Changes in elongation rates were reflected by dramatic changes in growth plate morphology in all cellular zones. This is the first study to directly correlate weight recovery during catch-up with growth rate responses at the level of the growth plate.

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Heme oxygenase (HO), the rate-limiting enzyme in the formation of bilirubin, is expressed in the lung and may serve as an antioxidant. This enzyme results in the formation of antioxidant bile pigments and the degradation of pro-oxidant heme. We wanted to evaluate the differences in expression of HO-1, the inducible form, and HO-2, the constitutive isoenzyme, during lung maturation and document whether lung HO expression was similar to that of other antioxidant enzymes. Lung total HO activity and HO-1 and HO-2 proteins as well as HO-1 and HO-2 mRNA were evaluated in animals from 16 d of gestation (e16.5) to 2 mo of age. Heme content was also evaluated because heme is the substrate of the reaction. HO-1 mRNA was maximal at e19.5and e20.5, whereas HO-2 mRNA was not changed throughout maturation. Lung HO-1 protein was highest on the first days of life and lowest in adults, whereas HO-2 protein was maximally expressed at postnatal d 5 and then declined to reach adult values. As to HO activity, there was a prenatal peak at e20.5, a second lesser peak at d 5, and thereafter a decline to adult values. Lung heme content was inversely correlated with HO activity or protein as the highest heme values were seen in adults with the lowest HO activity. In response to hyperoxia, HO-1 mRNA was induced only in the adult lungs. A better understanding of the maturational regulation of lung HO will define a role for HO in newborns at risk for oxygen toxicity.

ISSN:0031-3998    

出版商:OVID    

年代:2003

数据来源: OVID