Cerebral hemodynamics during the induction of antenatal periventricular leukomalacia by hemorrhagic hypotension in chronically instrumented fetal sheep

High Expression of Adrenal Cortisol Synthases Is Acquired After Intrauterine Inflammation in Periviable Sheep Fetuses

Context

Intrauterine inflammation, a representative stressor for the fetus, has been shown to alter the hypothalamus-pituitary-adrenal (HPA) axis reactivity in preterm fetuses and increase postnatal cortisol production. However, the mechanism of this alteration has not yet been elucidated.

Objective

We aimed to clarify the effects of endotoxin-induced intrauterine inflammation on the HPA axis of periviable sheep fetuses.

Methods

Fetal sheep (0.63 term) were divided into 2 groups: (1) the endotoxin group, in which the endotoxin was injected into the amniotic fluid; and (2) the control group, in which the saline solution was injected instead. A corticotropin-releasing hormone (CRH) challenge test was performed on the third day after injection to evaluate the cortisol-producing capacity of each group. Gene expression levels in the fetal adrenal glands of each group were analyzed by RNA-seq.

Results

The cortisol levels were significantly higher in the endotoxin group than in the control group after CRH challenge (P = .02). There were no significant differences in the responsiveness of adrenocorticotropin and cortisone between the 2 groups. Gene expression levels of the following enzymes involved in cortisol synthesis were significantly elevated in the endotoxin group: cytochrome P450 family (CYP) 11 subfamily A member 1 (log2FC 1.75), CYP 17 subfamily A member 1 (log2FC 3.41), 3β-hydroxysteroid dehydrogenase type I (log2FC 1.13), steroidogenic acute regulatory protein (log2FC 1.09), and CYP 21 (log2FC 0.89).

Conclusion

Periviable fetuses exposed to inflammation in utero have altered the responsiveness of the HPA axis with increased expression of enzymes involved in cortisol synthesis in the adrenal gland.

Monitoring of cerebral haemodynamics in newborn infants

The most important cerebrovascular injuries in newborn infants, particularly in preterm infants, are cerebral haemorrhage and ischemic injury. The typical cerebral vascular anatomy and the disturbance of cerebral haemodynamics play important roles in the pathophysiology. The term 'cerebral haemodynamics' includes cerebral blood flow (CBF), cerebral blood flow velocity, and cerebral blood volume (CBV). Therapy aimed at changing vascular anatomy is not available. Therefore, prevention of disturbances in CBF and CBV is pivotal. However, continuous monitoring of CBF and CBV is still unavailable for clinical use. Tissue oxygenation may be used as a surrogate for CBF, although precision is still questionable. General knowledge of the regulation of CBF and CBV is important. Although this knowledge is still incomplete, especially regarding autoregulation and the exact role of CBV, it is still useful. Using it even without knowing the exact level of CBF and CBV, it is possible to aim to keep CBF and CBV stable. Future research should focus on development of monitoring tools, gaining more insight in neonatal cerebral autoregulation, and demonstrating clinical benefits of a 'cerebral perfusion-oriented' therapy.

Effect of intrauterine inflammation on fetal cerebral hemodynamics and white-matter injury in chronically instrumented fetal sheep

OBJECTIVE

The purpose of this study was to analyze the effects of intrauterine inflammation on cerebral hemodynamics and white-matter injury in premature fetal sheep.

STUDY DESIGN

Fetuses were given an intravenous infusion of granulocyte colony-stimulating factor and an intraamniotic infusion of endotoxin; the fetuses were then assigned randomly to an acute hemorrhage group, an exchange transfusion group, or a control group. During each insult, the cerebral hemodynamics were assessed with near-infrared spectroscopy. Finally, the fetuses were processed for neuropathologic analysis and compared statistically.

RESULTS

Necrotizing funisitis and chorioamnionitis were induced in all the fetuses. A significant decrease in the blood oxygen content and an increase in the brain total hemoglobin level were observed after the endotoxin infusion. Soon after hemodynamic insult, the fetuses in both the acute hemorrhage and the exchange transfusion groups showed an abrupt decrease in the total brain hemoglobin level; 4 of the 5 fetuses in each treatment group, but none of the fetuses in the control group, exhibited periventricular leukomalacia.

CONCLUSION

Hemorrhagic hypotension or anemic hypoxemia might induce a sudden cessation of fetal brain-sparing effects through progressive inflammatory hypoxemia, which results in focal white-matter injuries.

Induction of necrotizing funisitis by fetal administration of intravenous granulocyte-colony stimulating factor and intra-amniotic endotoxin in premature fetal sheep

The purpose of the present study was to determine whether experimental intrauterine inflammation could induce necrotizing funisitis, a severe, chronic inflammation of the umbilical cord. Fetuses, randomly divided into four groups (n = 4 each), were infused with 50 mug/d of granulocyte-colony stimulating factor (G-CSF) intravenously on d 125-129 of gestation (G-CSF group), 20 mg of endotoxin into the amniotic cavity on d 127 gestation (endotoxin group), both G-CSF and endotoxin (G-CSF + endotoxin group), or only saline (control group). On d 130 of gestation, the umbilical cords were processed for histologic analysis, scored for degree of inflammation, and compared statistically. At birth, the blood polymorphonuclear leukocyte counts in G-CSF and G-CSF + endotoxin groups were significantly higher than those in endotoxin and control groups (p < 0.05). The inflammatory score of the umbilical cord in G-CSF + endotoxin group was significantly higher than those in the other three groups (p < 0.05). All the fetuses in G-CSF + endotoxin group had necrotizing funisitis, but none of the fetuses in the other three groups developed this condition. An increase in blood polymorphonuclear leukocytes before their activation in the umbilical cord is probably essential for experimentally inducing necrotizing funisitis.