The newborn rat gastric emptying rate is volume and not developmentally dependent.

BACKGROUND: Gastric residuals are a common finding in enterally fed preterm neonates and traditionally thought to reflect immaturity-related delayed gastric emptying. Adult human data suggest that the meal volume regulate the gastric emptying rate, but early in life, this has not been adequately evaluated. The goal of this study was to study the rat postnatal changes in gastric emptying rate and the strain-induced effect on muscle contraction. We hypothesized that the stomach content volume and not developmental factors determines the newborn gastric emptying rate, via the Rho-kinase 2 (ROCK-2) pathway. METHODS: Gastric volume and emptying rate measurements were obtained by ultrasound at different postprandial times and the wall strain-dependent changes in muscle contraction were evaluated ex vivo. KEY RESULTS: The newborn rat gastric emptying rate was unrelated to postnatal age, maximal 30 min postprandial, and directly proportional to content volume. In vitro measurements showed that the agonist-induced gastric muscle contraction was directly proportional to the stomach wall strain. These changes were mediated via upregulation of ROCK-2 activity. CONCLUSIONS & INFERENCES: The newborn rat gastric emptying rate is not developmentally regulated, but dependent on the content volume via wall strain-induced ROCK-2 activation. Further clinical studies addressing the content volume effect on the rate of gastric emptying are warranted, to enhance feeding tolerance in preterm neonates.

Age-dependent changes in the regulation of cyclooxygenases in the gastrointestinal tract after gram-negative endotoxemia.

BACKGROUND: Cyclooxygenases (COXs) modulate prostaglandin synthesis in the gastrointestinal tract. Prostaglandins have been shown to have a cytoprotective effect on bowel mucosa in adults, but no similar data are available in neonates. Thus, the purpose of the current study was to evaluate age-dependent changes in gastrointestinal tract COX regulation after Escherichia coli lipopolysaccharide exposure in rats. METHODS: Stomach, small bowel, and large bowel COX-1 and COX-2 mRNA levels (reverse transcription polymerase chain reaction technique) and protein content (Western blot) were obtained from neonates (younger than 3 days old) and adult rats 18 hours after exposure to E. coli O111:B4 lipopolysaccharide toxin. Untreated animals served as controls. RESULTS: Stomach, small bowel, and large bowel tissue COX-1 mRNA levels in the newborn were significantly lower (P < 0.01) than in the adult. No age-dependent differences were found for COX-2 mRNA levels. After lipopolysaccharide exposure, no significant changes in COX-1 levels were seen at either age, whereas COX-2 mRNA levels were increased only in the stomach for both ages. Western blot analysis of small bowel tissue for COX-1 and COX-2 showed no lipopolysaccharide-induced changes in protein content, but the COX-1 content was significantly lower in the newborn (P < 0.01). CONCLUSIONS: In the rat, COX expression in the gastrointestinal tract is regulated in an age-dependent fashion. Lower COX-1 expression and a lack of observable increase in COX-2 mRNA levels in the newborn small bowel after endotoxemia may render the bowel more susceptible to bowel injury early in life.

[Critical analysis of the use of corticosteroids in the neonatal period] / Análise crítica do uso de esteróides no período neonatal.

OBJECTIVE: To review the use of corticosteroids in the treatment of newborns with chronic lung disease, adrenal insufficiency and upper airway edema. SOURCES: Review of the available medical literature on the use of corticosteroids in newborns. SUMMARY OF THE FINDINGS: Although there is evidence of short-term clinical improvement of chronic lung disease with the administration of dexamethasone, the available literature did not show significant reduction in neonatal morbidity and mortality associated with this condition. CONCLUSIONS: The use of corticosteroids must be carefully analyzed and restricted to the treatment of severe cases, since these drugs may produce irreversible effects on the nervous system and neurological development of newborns.

Effects of in vitro fertilization on low birth weight, preterm delivery, and multiple birth.

PURPOSE: To quantify the contribution of in vitro fertilization (IVF) on changes in the rates of low birth weight (LBW), preterm delivery, very low birth weight, and multiple births during the past 3 years. METHODS: Data on IVF pregnancies from 1994 to 1996 within Alberta were reviewed. Population data were obtained from the Provincial notice of a live or stillbirth. RESULTS: The IVF component of increased LBW rate in the province was 17.8% for infants <2500 g and 43.5% for those born <1500 g. IVF accounted for 10.5% of the provincial rate increase in deliveries <37 weeks' gestation and 66.2% of those <30 weeks' gestation. IVF accounted for 21.4% of the twins and all of the sets of triplets in the province. CONCLUSION: During a 3-year period IVF has affected the incidence of LBW, preterm delivery, and multiple birth. IVF is a substantial contributor to changes in very low birth weight and delivery before 30 weeks, which is partly related to multiple births.

Effects of central apnea on cerebral blood flow velocity in healthy term infants.

We evaluated a new method of monitoring cerebral blood flow velocity (CBFV) and described changes in CBFV in relation to central apnea in 17 healthy term infants. The area under the velocity curve during apnea did not change, whereas area under the velocity curve per the waveform showed a significant difference, suggesting that stability is maintained through an increase in CBFV with each heartbeat. The maintenance of cerebral hemodynamics during isolated central apnea supports the assumption that these episodes are benign.

Thoracic electric bioimpedance measurement of cardiac output in the newborn infant.

To evaluate thoracic electric bioimpedance as a noninvasive method for measuring cardiac output, we compared the bioimpedance measurements with those obtained by means of the thermodilution indicator cardiac output technique in seven preterm and term lambs; we also studied 17 term and preterm infants. Sixty-seven simultaneous bioimpedance and thermodilution cardiac output measurements were obtained in the animals after intravascular volume expansion (saline solution infusion) and contraction (phlebotomy). A significant correlation between the cardiac output measurements by the two methods (0.82; p less than 0.001) was observed. In neonates, the observed cardiac output was 198 +/- 46 ml/kg.min in the preterm infants and 178 +/- 46 ml/kg.min in the term infants. Extrapolating animal data to the neonates, we found the thoracic segment length recommended (the average of 29% of body length and electrode distance) to be accurate. These data indicate that bioimpedance cardiac output measurement (1) is comparable to measurement by the thermodilution indicator technique in the newborn animal and (2) may be suitable for use in infants and children.

Changes in pulmonary function during the diuretic phase of respiratory distress syndrome.

To evaluate the relationship between improvement in pulmonary function and spontaneous diuresis in respiratory distress syndrome, nine premature infants requiring mechanical ventilation for RDS were studied at a mean age of 11.9 hours prior to the onset of diuresis, at onset of diuresis, at maximum urine output (mean age 44.9 hours), and at 24 hours after maximum urine output. Prior to diuresis functional residual capacity decreased from mean +/- SEM of 16.2 +/- 2 to 13.3 +/- 1.2 ml/kg, and dynamic lung compliance decreased from 2.5 +/- 0.3 to 1.8 +/- 0.3 ml/cm H2O (P less than 0.05), indicating that the respiratory disease was worsening. There was no significant change in alveolar-arterial oxygen gradient, peak inflating pressure, or rate of intermittent mandatory ventilation over this period. At the time of maximum urine output, however, FRC had increased 36% (P less than 0.05). CL had increased by 60% to 2.8 +/- 0.4 ml/cm H2O (P less than 0.025), AaDO2 had decreased from 246 +/- 27 to 184 +/- 30 torr (P less than 0.005), and PIP had decreased from 14.9 +/- 2.2 to 11.3 +/- 2.1 cm/H2O (P less than 0.05). On follow-up study 24 hours after maximum urine output, there was no further significant improvement in FRC, CL or PIP, but IMV rate and AaDO2 continued to decrease. These data show that the pulmonary function in RDS deteriorates until the onset of diuresis, after which it rapidly improves. This diuresis may represent the removal of excess lung liquid and seems necessary for improvement in RDS.