ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Whereas bacterial polysaccharides, classified as T-cell-independent antigens, elicit protective antibodies in adults, booster injections fail to produce an augmented response or promote antibody class switching. Because T-cell-dependent antigens, typically proteins, both produce boosted antibody levels and promote antibody class switching, it has been considered highly desirable to attempt to convert the T-cell-independent polysaccharide antigens into T-cell-dependent antigens, particularly for use in high-risk groups. A number of clinical trials now report the efficacy of conjugate vaccines in inducing the production of antibody in response to a number of previously poorly immunogenic–mainly T-cell-independent— antigens. In addition to conjugate vaccines containing bacterial polysaccharides, vaccines containing relevant peptides from a variety of pathogens are also being formulated and investigated. Questions remain, however, regarding their synthesis, use, and efficacy. The best ages for vaccine administration and selection of the optimal protein carrier are still under investigation, as are questions regarding the use of adjuvants, which can greatly affect the vaccine's potency. Spacing and size of epitope and size and composition of the final structure also must be considered; the importance of molecular size and aggregation of antigen in increasing immunogenicity have been well documented. These questions must be addressed for the much-needed development of conjugate vaccines against some common infections worldwide, including malaria, bacterial meningitis, and infections fromPseudomonas aeruginosaandNeisseria gonorrhoeaebecause of increasing susceptibility to these infections and resistance of the pathogens to chemotherapeutic agents and/or antibiotics.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

In situ cross-sectional morphology of the ductus venosus and related vessels was studied after rapid whole-body freezing of the fetal and neonatal rat. In the fetus, the ductus venosus was open widely, connecting the umbilical sinus and the inferior vena cava. The diameter of the ductus venosus was 50% of the diameter of the umbilical sinus. The ductus venous joined the left dorsal side of the inferior vena cava. A thin, short, membrane-like edge was present at the inner junction of the ductus venosus and the inferior vena cava, presumably effecting laminar flow of the ductus venosus blood to the left side of the thoracic inferior vena cava. A very prominent eustachian valve was present at the junction of the inferior vena cava and the right atrium, presumably directing its flow to the opening of the foramen ovale. After birth, the ductus venosus narrowed rapidly and closed completely in 2 d. The closing ductus venosus was tubular, with the cranial end slightly wider than the caudal portion. Localized constriction was not present. These observations showed the structural substrate for preferential flow from the ductus venosus to the foramen ovale and left atrium in the fetus and did not support localized sphincter mechanism in postnatal closure of the ductus venosus.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To determine the fate of the atrioventricular endocardial cushions in cardiac development, we used staining methods for extracellular fibronectin, which is abundant in the endocardial cushions, and actin, which is abundant in the myocytes. White Leghorn chick embryo hearts were harvested at Hamburger and Hamilton stages 26 to 36, and serial sections of the atrioventricular valve region were stained. Before atrioventricular valve formation, fibronectin and actin staining reveal separation between the fibronectin-rich endocardial cushions and the actin-rich myocardial layer. The developing mitral valve leafets at all of the observed stages contain a fibronectinrich matrix but no actin-rich myocytes. In contrast, the tricuspid band includes both fibronectin matrix and actinrich cells. We conclude that the mitral valve leaflets in the chick form predominantly from the endocardial cushion tissue, and the tricuspid band receives contributions from both the endocardial cushions and surrounding myocardium.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We developed an experimental rat model of congenital diaphragmatic hernia (CDH) to elucidate the etiology and pathogenesis of this serious congenital anomaly in humans and in particular to study the effects of a short period of artificial ventilation on the CDH lung in relation to antioxidant defense mechanisms. CDH was induced in about 60% of the offspring by maternal exposure to 2,4-dichlorophenylp-nitrophenylether (Nitrofen) during pregnancy. This herbicide resembles thyroid hormone in chemical structure. The lungs of fetal rats (d 19, 20, 21, and 22) were examined for protein and DNA content and activity of superoxide dismutase, catalase, and glutathioae peroxidase (GPX). The same parameters were assessed in tracheotomized newborn rats after pressure-controlled artificial ventilation with either room air or pure oxygen during a short period of 5 h. In both CDH rats and controls, wet lung weight increased during gestation. At term, CDH rats had significantly lower mean lung weights than controls. Neither group differed in protein and DNA content per mg lung or superoxide dismutase, catalase, and GPX activity before and at birth. After artificial ventilation of neonates with air and pure oxygen, superoxide dismutase activity tended to decrease, whereas catalase activity remained virtually unchanged in the CDH long. However, GPX activity in the CDH lung was reduced to 80% of initial activity at term after ventilation with air and to 70% with pure oxygen. The present finding of a decline in GPX activity in this animal model after a short period of artificial ventilation may indicate that the CDH rat neonate is at risk to develop oxygen-related lung damage.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The ability of erythrocytes from newborn babies and adults to maintain reduced glutathione levels during oxidative stress was studied.In vitroincubation of erythrocytes with H2O2with or without inactivation of catalase, caused a rapid depletion of reduced glutathione (GSH) and concomitant accumulation of oxidized glutathione followed by recovery of GSH and fall of oxidized glutathione to initial values in all subjects. Inactivation of catalase resulted in a 50% loss of intracellular glutathione (p< 0.005), a larger maximum GSH depletion (p< 0.05), and a longer GSH recovery time (p< 0.005). Erythrocytes from newborn babies showed a smaller maximum GSH depletion (p< 0.05) and a shorter GSH recovery time (p< 0.005) compared with those from adults. These differences between the newborn and adult groups persisted after inactivation of catalase. An increase in maximum GSH depletion and GSH recovery time (p< 0.005) was observed when a lower hematocrit was used for these GSH recovery studies. Effective glutathione recycling in erythrocytes may protect immature tissues of the newborn baby from peroxidative damage.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The classic “biphasic‘’ ventilatory response to 15% O2was previously observed in preterm infants who were Large compared with those in the intensive care nursery today. We hypothesized that in the smaller infant (≤1500 g) the response might be closer to that of the fetus, with no initial increase in ventilation. Thus, we studied 14 healthy preterm infants ± 1500 g [birth weight 1220 ± 63 g (mean ± SEM); gestationl age 29 ± 0.4 wlq postnatal age 17 ± 3 d] during rapid eye movement and quiet sleep. Ventilation was measured using a nosepiece and a flowthrough system. Sleep states were defined using EEC, electro-oculogram, and body movements. After a control period in 21% 02 (3 min), infants breathed 15% O2, for 5 min. In rapid eye movement sleep, minute ventilation decreased from 0.186 ± 0.020 (control) to 0.178 ± 0.021 (30 s) to 0.171 ± 0.017 (1 min;p= 0.03), to 0.145 ± 0.016 (3 min;p= 0.002), and to 0.129 ± 0.011 1 ± min−1kg−1(5 min;p= 0.004). In quiet sleep, it decreased from 0.173 ± 0.019 (control) to 0.164 ± 0.019 (30 s), to 0.166 ± 0.019 (1 ± min−1to 0.148 ± 0.013 (3 min;p= 0.03) and to 0.146 ± 0.012 1 ± min−1± kg−1(5 min;p=0.04). These changes in ventilation were primarily related to a decrease in frequency in rapid eye movement [38 ± 2 (control)versus28 ± 3 (5 min);p0.01 and in quiet sleep [36 ± 5 (control) versus 27 ±3(5 min);p= 0.02]. Changes in tidal volume were negligible. These findings suggest that the classic biphas response to hypoxia is not observed in very small preterm infants. These infants show only a sustained decrease in ventilation with low O2. We speculate that the response reflects a more pronounced inhibitory mechanism induced by hypoxia at this gestational age, representing an intermediate profile between that observed in the fetus and that present in larger neonates.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Newborn rats prenatally treated with TRH or the combination of TRH+DEX have lower long antioxidant enzyme activities at birth than control newborn but are able to induce an adaptive antioxidant enzyme response to hyperoxic exposure of similar or even greater magnitude compared to O2control offspring. Because of this greater antioxidant enzyme response, we hypothesized that the hormonally pretreated newborn might demonstrate superior tolerance to prolonged high O2exposure. However, when placed in >95% O2at birth, the survival rates were consistently lower in the TRH- and TRH+DEX-treated pups at all time periods in hyperoxia from 9 d (control = 74 of 92 (80%); TRH+DEX = 32 of 47 (68%); TRH = 29 of 48 (60%)p< 0.05] to 14 d (control = 43 of 92 (47%); TRH+DEX = 11 of 47 (23%); TRH = nine of 48 (19%); (p< 0.05). Other evidence of poorer O2tolerance in the prenatal hormone-treated pups included a greater incidence of intraalveolar edema and elevated lung conjugated dienes, an index of lipid peroxidation, at 3, 5, and 7 d of O2exposure. There was also a persistent elevation in 3,5,3‘-triiodo-L-thyronine and thyroxine serum levels in the 10-d-old TRH treated offspring. We conclude that prenatal TRH treatment, possibly working through the secretion of 3,5,3’-triiodo-L-thyronine and thyroxine, has some important lasting postnatal effect (not completely reversed by dexamethasone) that predisposes newborn rats to greater O2radical-induced lung sequelae of prolonged hyperoxic exposure.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The aim of this study was to reappraise the effects of maternal meperidine administration on breathing pattern during the first hours of life taking into account the state of alertness. Because breathing instability is more pronounced during active sleep, we hypothesized that meperidine administration might create a greater risk for respiratory instability during active sleep, the prominent sleep state in new borns. We studied eight full-term, healthy new borns whose mothers had received a continuous i.v. infusion of meperidine (81 ± 9 mg) that was terminated 5.5 ± 2.1 h before delivery. These infants were compared with a control group of eight full-term newbons whose mothers did not receive any opioids. In both groups, all babies were delivered vaginally after a normal labor and had Apgar scores of 9 or 10 at 1 and 5 min. Neonatal gastric secretion and maternal venous and umbilical venous blood were sampled at delivery for determination of meperidine concentration. From 60 to 300 min after delivery, behavioral sleep states and thoracic and abdominal movement as well as transcutaneous arterial oxygen saturation (SaO2) were monitored continuously. The number of apneic spells lasting more than 3 s during 100 min of recording and the percentage of time with SaO2below 90% in each sleep state were recorded. During quiet sleep, all respiratory variables were similar in both groups. During active sleep, there were significantly more apneic episodes (37.1 ± 25.1versus11.2 ± 13.9) and a higher percentage of time with Sao2< 90% (14.3 ± 16.7%versus13 ± 1.5%) in the meperidine group than in the control group (p< 0.01). In addition, the percentage of time with Sao2, < 90% was significantly correlated with maternal meperidine dose (p< 0.02), drug-delivery interval (p< 0.01), and gastric concentration of meperidine (p< 0.01). These data show that maternal administration of meperidine induces respiratory abnormalities in healthy, full-term newborns that occur only during active sleep. This result indicates that the state of alertness has to be characterized during the monitoring of long-term neonatal respiratory effects of any narcotic agent. In addition, we speculate that maternal meperidine administration may provoke more severe respiratory disturbances in at-risk neonates and that respiratory monitoring during the first hours of life may be useful in these newborns.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We have investigated the effect of changing environmental temperature on metabolic rate, sleep state, and water loss in a longitudinal study of 22 lightly clothed babies from 2 d to 3 mo of age. Studies were performed in a modified barometric plethysmograph while recording sleep state, oxygen consumption, and skin and axillary temperatures. Oxygen consumption was higher in rapid eye movement sleep than in quiet sleep at all ages and varied widely between infants at each temperature. Within the first week, there was a 19% rise in oxygen consumption on cooling to 19–22°C during rapid eye movement sleep and a 6% rise during quiet sleep. The median duration of quiet sleep periods was reduced from 17 to 12 min on cooling within the first week. No such change was seen at 1, 2, and 3 mo. Axillary temperature was reduced at 3 mo during cooling. This may be a part of normal patterns of change in temperature during sleep, unrelated to cooling. At each age, total evaporative water loss fell linearly with falling environmental temperature both within and below the temperature range at which metabolic rate was minimal. The evaporative water losses were greater than expected and suggested that sweating was occurring, both at temperatures at which metabolic rate was minimal and at those at which it was increased. The metabolic response to cooling and the process of sweating appear to be in dynamic equilibrium across this temperature range. Thus, it was not possible to define a temperature range over which both metabolic rate and evaporative water loss were at minimum values.

ISSN:0031-3998    

出版商:OVID    

年代:1992

数据来源: OVID