Fetal heart rate variability and brain stem injury after asphyxia in preterm fetal sheep

This study was undertaken to determine the mechanisms mediating changes in fetal heart rate variability (FHRV) during and after exposure to asphyxia in the premature fetus. Preterm fetal sheep at 0.6 of gestation (91 +/- 1 days, term is 147 days) were exposed to either sham occlusion (n = 10) or to complete umbilical cord occlusion for either 20 (n = 7) or 30 min (n = 10). Cord occlusion led to a transient increase in FHRV with abrupt body movements that resolved after 5 min. In the 30 min group there was a marked increase in FHRV in the final 10 min of occlusion related to abnormal atrial activity. After reperfusion, FHRV in both study groups was initially suppressed and progressively increased to baseline levels over the first 4 h of recovery. In the 20 min group this improvement was associated with return of normal EEG activity and movements. In contrast, in the 30 min group the EEG was abnormal with epileptiform activity superimposed on a suppressed background, which was associated with abnormal fetal movements. As the epileptiform activity resolved, FHRV fell and became suppressed for the remainder of the study. Histological assessment after 72 h demonstrated severe brain stem injury in the 30 min group but not in the 20 min group. In conclusion, during early recovery from asphyxia, epileptiform activity and associated abnormal fetal movements related to evolving neural injury can cause a confounding transient increase in FHRV, which mimics the normal pattern of recovery. However, chronic suppression of FHRV was a strong predictor of severe brain stem injury.     

Nonimmune hydrops fetalis and activation of the renin-angiotensin system after asphyxia in preterm fetal sheep

This study examined the hypothesis that the development of hydrops fetalis after asphyxia in the 0.6 gestation sheep fetus would be associated with activation of the fetal renin-angiotensin system (RAS). Fetuses were randomly assigned to either sham occlusion (n = 7) or to 30 min of asphyxia induced by complete umbilical cord occlusion for 30 min (n = 8). Asphyxia led to severe bradycardia and hypotension that resolved after release of occlusion. After occlusion, plasma renin concentration was significantly increased in the asphyxia group compared with controls (P < 0.005) after 3 min (16.3 +/- 5.3 vs. 4.1 +/- 1.3 ng. ml(-1). h(-1)), and 72 h (30.6 +/- 6.3 vs. 3.7 +/- 1.2 ng. ml(-1). h(-1)). Renal renin concentrations and mRNA levels were significantly greater in the asphyxia group after 72 h of recovery. All fetuses in the asphyxia group showed generalized tissue edema, ascites, and pleural effusions after 72 h of recovery. In conclusion, asphyxia in the preterm fetus caused sustained activation of the RAS, which was associated with hydrops fetalis.     

Linkage between the CYP2C8 and CYP2C9 genetic polymorphisms

Cytochrome P450 (CYP) 2C8 and 2C9 are polymorphic enzymes. The CYP2C8*3 and CYP2C9*2 are the major variant alleles in Caucasian populations. The enzymes encoded by these variant alleles have impaired function for the metabolism of several drug substrates. In the present study 1468 subjects that were used as population-based controls in the Stockholm Heart Epidemiology Program (SHEEP) were genotyped by allelic discrimination using a 5'-nuclease assay for CYP2C8*1, 2C8*3, 2C9*1, 2C9*2, and 2C9*3 variant alleles in which the frequencies appeared to be 0.91, 0.095, 0.83, 0.11, and 0.066, respectively. Approximately, 96% of the subjects with CYP2C8*3 allele also carried a CYP2C9*2 and 85% of the subjects that had CYP2C9*2 variant also carried a CYP2C8*3. The number of subjects carrying both of the CYP2C8*1*3 and CYP2C9*1*2 was 4.5-fold higher than expected. This strong association may be of importance especially for the metabolism of common substrates of CYP2C8 and CYP2C9 like arachidonic acid that produces physiologically active metabolites.     

Fetal acidosis and hypotension during repeated umbilical cord occlusions are associated with enhanced chemoreflex responses in near-term fetal sheep.

This study examined the hypothesis that repeated episodes of brief but severe hypoxia would not attenuate the chemoreflex-mediated rapid initial fall in fetal heart rate (FHR) and, further, that greater hypoxic stress, as shown by hypotension and metabolic acidosis, would be associated with an enhanced chemoreflex response. Chronically instrumented, near-term fetal sheep received 1 min total umbilical cord occlusion either every 5 min for 4 h (1:5 group; n = 8) or every 2.5 min (1:2.5 group; n = 8) until mean arterial blood pressure fell to <20 mmHg on two successive occlusions. Umbilical cord occlusion caused variable decelerations, with sustained hypertension in the 1:5 group and little change in acid-base status (pH 7.34 +/- 0.03 after 4 h). In contrast, the 1:2.5 group showed progressive hypotension and metabolic acidemia (pH 6.92 +/- 0.04 after the last occlusion). The 1:2.5 group showed a significant increase in the rate of initial fall in FHR during the occlusion series, which was greater than the 1:5 group in the last 30 min of the occlusion series (9.4 +/- 1.4 vs. 3.5 +/- 0.3 beats.min(-1).s(-1); P < 0.01), with a greater fall in FHR (71.9 +/- 6.5 vs. 47.0 +/- 8.7 beats/min; P < 0.05). In summary, this study demonstrated that repetitive laborlike cord occlusions, which led to severe fetal compromise, were associated with an increase in the slope and magnitude of the initial FHR deceleration. These findings support the concept of the chemoreflex as a central, robust component of fetal adaptation to severe hypoxia.     

Subclinical exposure to low-dose endotoxin impairs EEG maturation in preterm fetal sheep

Exposure to chorioamnionitis is strongly associated with neurodevelopmental disability after premature birth; however, it remains unclear whether subclinical infection affects functional EEG maturation. Chronically instrumented 103-104-day-old (0.7 gestational age: term 147 days) fetal sheep in utero were randomized to receive either gram-negative LPS by continuous low-dose infusion (100 ng iv over 24 h, followed by 250 ng/24 h for 4 days; n = 6) or the same volume of normal saline (n = 9). Arterial plasma cortisol, ACTH, and IL-6 were measured. The delta (0-3.9 Hz), theta (4-7.9 Hz), alpha (8-12.9 Hz), and beta (13-22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken after 10 days for histopathology. There were no changes in blood gases, cardiovascular variables, or EEG power during LPS infusion, but a transient rise in plasma cortisol and IL-6 (P < 0.05). LPS infusion was associated with loss of the maturational increase to higher frequency activity, with reduced alpha and beta power, and greater delta power than saline controls from 6 to 10 days (P < 0.05). Histologically, LPS was associated with increased numbers of microglia and TNF-α-positive cells in the periventricular white matter and frontoparietal cortex, increased caspase-3-positive cells in white matter, but no loss of CNPase-positive oligodendrocytes, Nurr-1 subplate cells, or gyral complexity. These data suggest that low-dose endotoxin exposure can impair EEG maturation in preterm fetal sheep in association with neural inflammation but without hemodynamic disturbances or cortical injury.     

Mathematical Elegance with Biochemical Realism: The Covarion Model of Molecular Evolution

There is an apparent paradox in our understanding of molecular evolution. Current biochemically based models predict that evolutionary trees should not be recoverable for divergences beyond a few hundred million years. In practice, however, trees often appear to be recovered from much older times. Mathematical models, such as those assuming that sites evolve at different rates [including a Γ distribution of rates across sites (RAS)] may in theory allow the recovery of some ancient divergences. However, such models require that each site maintain its characteristic rate over the whole evolutionary period. This assumption, however, contradicts the knowledge that tertiary structures diverge with time, invalidating the rate-constancy assumption of purely mathematical models. We report here that a hidden Markov version of the covarion model can meet both biochemical and statistical requirements for the analysis of sequence data. The model was proposed on biochemical grounds and can be implemented with only two additional parameters. The two hidden parts of this model are the proportion of sites free to vary (covarions) and the rate of interchange between fixed sites and these variable sites. Simulation results are consistent with this approach, providing a better framework for understanding anciently diverged sequences than the standard RAS models. However, a Γ distribution of rates may approximate a covarion model and may possibly be justified on these grounds. The accurate reconstruction of older divergences from sequence data is still a major problem, and molecular evolution still requires mathematical models that also have a sound biochemical basis. Received: 13 February 2001 / Accepted: 22 May 2001     

Autoimmunity against INS-IGF2 Protein Expressed in Human Pancreatic Islets

Insulin is a major autoantigen in islet autoimmunity and progression to type 1 diabetes. It has been suggested that the insulin B-chain may be critical to insulin autoimmunity in type 1 diabetes. INS-IGF2 consists of the preproinsulin signal peptide, the insulin B-chain, and eight amino acids of the C-peptide in addition to 138 amino acids from the IGF2 gene. We aimed to determine the expression of INS-IGF2 in human pancreatic islets and autoantibodies in newly diagnosed children with type 1 diabetes and controls. INS-IGF2, expressed primarily in beta cells, showed higher levels of expression in islets from normal compared with donors with either type 2 diabetes (p = 0.006) or high HbA1c levels (p < 0.001). INS-IGF2 autoantibody levels were increased in newly diagnosed patients with type 1 diabetes (n = 304) compared with healthy controls (n = 355; p < 0.001). Displacement with cold insulin and INS-IGF2 revealed that more patients than controls had doubly reactive insulin-INS-IGF2 autoantibodies. These data suggest that INS-IGF2, which contains the preproinsulin signal peptide, the B-chain, and eight amino acids of the C-peptide may be an autoantigen in type 1 diabetes. INS-IGF2 and insulin may share autoantibody-binding sites, thus complicating the notion that insulin is the primary autoantigen in type 1 diabetes.     

Prognosis and early management of birth injuries to the brachial plexus.

Twenty-four cases of birth injury to the brachial plexus were seen in 21 infants over 15 years. Obstetric complications were common, and in 11 cases traction was needed to deliver the shoulders. Three out of every four arms fully recovered after exercises. Splints were not needed. Reconstructive procedures were performed on three permanently paralysed arms when the children were aged about 4. There was no way of predicting which patients would recover. The muscles supplied by the suprascapular nerve were paralysed in all patients, and this paralysis persisted in those whose arms failed to recover fully.     

Maturation of the mitochondrial redox response to profound asphyxia in fetal sheep

Fetal susceptibility to hypoxic brain injury increases over the last third of gestation. This study examined the hypothesis that this is associated with impaired mitochondrial adaptation, as measured by more rapid oxidation of cytochrome oxidase (CytOx) during profound asphyxia. METHODS: Chronically instrumented fetal sheep at 0.6, 0.7, and 0.85 gestation were subjected to either 30 min (0.6 gestational age (ga), n = 6), 25 min (0.7 ga, n = 27) or 15 min (0.85 ga, n = 17) of complete umbilical cord occlusion. Fetal EEG, cerebral impedance (to measure brain swelling) and near-infrared spectroscopy-derived intra-cerebral oxygenation (ΔHb = HbO(2) - Hb), total hemoglobin (THb) and CytOx redox state were monitored continuously. Occlusion was associated with profound, rapid fall in ΔHb in all groups to a plateau from 6 min, greatest at 0.85 ga compared to 0.6 and 0.7 ga (p<0.05). THb initially increased at all ages, with the greatest rise at 0.85 ga (p<0.05), followed by a progressive fall from 7 min in all groups. CytOx initially increased in all groups with the greatest rise at 0.85 ga (p<0.05), followed by a further, delayed increase in preterm fetuses, but a striking fall in the 0.85 group after 6 min of occlusion. Cerebral impedance (a measure of cytotoxic edema) increased earlier and more rapidly with greater gestation. In conclusion, the more rapid rise in CytOx and cortical impedance during profound asphyxia with greater maturation is consistent with increasing dependence on oxidative metabolism leading to earlier onset of neural energy failure before the onset of systemic hypotension.