Onset Of Hypoxia Research Articles

THE HYPOXIC BRAIN

While high altitude mountain climbers know that the human brain can eventually adjust to low oxygen levels, sadly the same is not true in the clinical setting. Within minutes of a stroke or heart failure, delicate neural tissue is already beginning to shut down as the processes that initially

Oxygen limited thermal tolerance in fish?--Answers obtained by nuclear magnetic resonance techniques.

In various phyla of marine invertebrates limited capacities of both ventilatory and circulatory performance were found to set the borders of the thermal tolerance window with limitations in aerobic scope and onset of hypoxia as a first line of sensitivity to both cold and warm temperature extremes. The hypothesis of oxygen limited thermal tolerance has recently been investigated in fish using a combination of non-invasive nuclear magnetic resonance (NMR) methodology with invasive techniques. In contrast to observations in marine invertebrates arterial oxygen tensions in fish were independent of temperature, while venous oxygen tensions displayed a thermal optimum. As the fish heart relies on venous oxygen supply, limited cardio-circulatory capacity is concluded to set the first level of thermal intolerance in fish. Nonetheless, maximized ventilatory capacity is seen to support circulation in maintaining the width of thermal tolerance windows. The interdependent setting of low and high tolerance limits is interpreted to result from trade-offs between optimized tissue functional capacity and baseline oxygen demand and energy turnover co-determined by the adjustment of mitochondrial densities and functional properties to a species-specific temperature range. At temperature extremes, systemic hypoxia will elicit metabolic depression, thereby widening the thermal window transiently sustained especially in those species preadapted to hypoxic environments.

Hydraulic Study of the Onset of Hypoxia in the Tone River Estuary

Field measurements were conducted to investigate the onset and growth of hypoxia in the Tone River Estuary. Vertical profiles of dissolved oxygen (DO), salinity, and temperature were measured along the deepest line of the estuary. Rates of oxygen consumption by water and sediment in a salt wedge were obtained using laboratory tests. The measurements showed that hypoxia frequently occurred in the front part of the salt wedge and expanded its area toward the river mouth during the summer when the river flow rate was small. The data also suggested that the onset of hypoxia was delayed by the estuarine circulation which supplied oxygen-rich seawater to the salt wedge. To simulate this phenomenon, a two-dimensional flow model in the vertical-longitudinal plane was constructed by transversely integrating the k-ε model equations. The results of model simulation for three months in the summer of 1997 closely matched the field data. The model simulation proved that DO degradation is highly correlated with the residence time of salt water in the estuary.

Transfusion-Related Acute Lung Injury Resulting From Designated Blood Transfusion Between Mother and Child

Transfusion-related acute lung injury (TRALI) is an underdiagnosed serious complication of blood transfusion characterized by the rapid onset of respiratory distress, hypoxia, and noncardiogenic pulmonary edema during or soon after blood transfusion. The presence of anti-HLA and/or antigranulocyte antibodies in the plasma of donors is implicated in the pathogenesis of TRALI. We report 2 cases of TRALI that were caused by designated blood transfusion between mothers and their daughters; one in a 4-month-old girl who received designated packed RBCs donated by her mother and the second in a 78-year-old mother who received blood from her daughter. In both cases, examination of mother’s serum revealed panel-reactive cytotoxic HLA antibodies. It is most likely that the mothers were sensitized from earlier pregnancy and produced HLA antibodies against the daughters’ paternally derived HLA antigens. Designated blood transfusion between multiparous mothers and children might add an additional transfusion-related risk owing to the higher likelihood of the HLA antibody-antigen specificity between mother and child.

Effect of neuronal nitric oxide synthase inhibition on CA 2+/calmodulin kinase kinase and CA 2+/calmodulin kinase IV activity during hypoxia in cortical nuclei of newborn piglets

The present study tests the hypothesis that cerebral tissue hypoxia results in increased Ca 2+/calmodulin (CaM) kinase kinase activity and that the administration of nitric oxide synthase inhibitors ( N-nitro- l-arginine [NNLA], or 7-nitroindazole sodium [7-NINA]) prior to the onset of hypoxia will prevent the hypoxia-induced increase in the enzyme activity. To test this hypothesis, CaM kinase kinase and CaM kinase IV activities were determined in normoxic, hypoxic, NNLA-treated hypoxic, and 7-NINA-treated hypoxic piglets. Hypoxia was induced (FiO 2=0.05−0.08×1 h) and confirmed biochemically by tissue levels of ATP and phosphocreatine. CaM kinase kinase activity was determined in a medium containing protein kinase and phosphatase inhibitors, calmodulin, and a specifically designed CaM kinase kinase target peptide. CaM kinase IV activity was determined by 33P-incorporation into syntide-2 in a buffer containing protein kinase and phosphatase inhibitors. Compared with normoxic animals, ATP and phosphocreatine levels were significantly lower in all hypoxic piglets whether or not pretreated with nitric oxide synthase inhibitors. There was a significant difference among CaM kinase kinase activity (pmol/mg protein/min) in normoxic (76.84±14.1), hypoxic (138.86±18.2, P<0.05 vs normoxia), NNLA-pretreated hypoxic (91.34±19.3; P=NS vs normoxia, P<0.05 vs hypoxia) and 7-NINA-pretreated hypoxic animals (100.12±23.3; P=NS vs normoxia, P<0.05 vs hypoxia). There was a significant difference among CaM kinase IV activity (pmol/mg protein/min) in normoxia (1270.80±126.1), hypoxia (2680.80±136.7; P<0.05 vs normoxia), NNLA-pretreated hypoxia (1666.00±154.8; P<0.05 vs normoxia, P<0.05 vs hypoxia), and 7-NINA-pretreated hypoxic (1712.9±231.5; P=NS vs normoxia, P<0.05 vs hypoxia). We conclude that the hypoxia-induced increase in CaM kinase kinase and CaM kinase IV activity is mediated by neuronal NOS-derived NO.

Another major US nuclear order for MHI

Pathogenesis of pulmonary hypertension is complex and involves activation of the transcription factor, hypoxia-inducible factor-1 (HIF-1) that shifts cellular metabolism from aerobic respiration to glycolysis, in part, by increasing the expression of its downstream target pyruvate dehydrogenase kinase-1 (PDK-1), thereby promoting a proliferative, apoptosis-resistant phenotype in pulmonary vascular cells. Activation of the nuclear hormone transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ), attenuates pulmonary hypertension and pulmonary artery smooth muscle cell (PASMC) proliferation. In the current study, we determined whether PPARγ inhibits HIF-1α and PDK-1 expression in human PASMCs.HPASMCs were exposed to normoxia (21% O2) or hypoxia (1% O2) for 2-72 hours ± treatment with the PPARγ-ligand, rosiglitazone (RSG, 10 μM).Compared to normoxia, HIF-1α mRNA levels were elevated in HPASMC at 2 hours hypoxia and reduced to baseline levels by 24-72 hours. HIF-1α protein levels increased following 4 and 8 hours of hypoxia and returned to baseline levels by 24 and 72 hours. PDK-1 protein levels increased following 24 hours hypoxia and remained elevated by 72 hours. RSG treatment at the onset of hypoxia attenuated HIF-1α protein and PDK-1 mRNA and protein levels at 4, 8 and 24 hours of hypoxia, respectively. However, RSG treatment during final 24 hours of 72-hour hypoxia, an intervention that inhibits HPASMC proliferation, failed to prevent hypoxia-induced PDK-1 expression.Hypoxia causes transient activation of HPASMC HIF-1α that is attenuated by RSG treatment initiated at hypoxia onset. These findings provide novel evidence that PPARγ modulates fundamental and acute cellular responses to hypoxia through both HIF-1-dependent and HIF-1-independent mechanisms.

Differential haemoglobin gene expression in the crustacean Daphnia magna exposed to different oxygen partial pressures.

The quantity and quality of the haemoglobin (Hb) of Daphnia magna is related to oxygen partial pressure in the water. Both the dynamics of hypoxia-induced Hb gene transcription, as well as Hb properties in animals incubated long-term at hyperoxia, normoxia and hypoxia, were investigated. Examination of Hb gene (dhb1-dhb3) transcription showed the expression of dhb2 and especially dhb3 to increase markedly approximately one hour after the onset of hypoxia, whereas dhb1 was expressed more or less constitutively. At an incubation close to anoxia, an onset of dhb3 transcription was found already after two minutes. In long-term incubated animals, concentration and oxygen affinity of Hb were lower at higher oxygen partial pressures. With decreasing oxygen availability, the subunit composition of Hb macromolecules changed. The share of the dhb2-encoded subunit, DHbF, increased already during moderate hypoxia. The increase of dhb3 mRNA (encoding DHbC) may be related to a transient increase of DHbC in the first days of hypoxia and/or to an additional coding of dhb3 for DHbD. The rise of DHbD, and particularly DHbA, only at severe hypoxia coincided with the increase of Hb oxygen affinity. The dhb1-encoded subunits DHbB and DHbE showed either a relatively moderate increase or even a decrease in concentration at hypoxia. In small animals with restricted homeostasis capabilities such as Daphnia, adaptation of the protein equipment seems to be a more effective strategy than allosteric modulator control.

The process of hypoxic induction of Daphnia magna hemoglobin: subunit composition and functional properties

The process of oxygen-dependent hemoglobin induction in Daphnia magna was studied over an 11-day period of hypoxia (ambient oxygen partial pressure: 3 kPa). Along with the increase of hemoglobin concentration in the hemolymph, hemoglobin became the dominant protein fraction in gel filtration experiments using extracts of whole animals. The size of the native aggregates was constant. However, subunit composition depended on the duration of hypoxia: the pattern of predominantly expressed subunits under hypoxia deviated from that of normoxic individuals. The varying degree of hypoxic induction for different hemoglobin subunits was confirmed by autoradiography. Along with changes in hemoglobin subunit composition, oxygen affinity of the respiratory protein increased. The dynamics of the hemoglobin induction process was analysed. Newly synthesized hemoglobin can be detected within 18 h after the onset of hypoxia. A marked increase in hemoglobin concentration is evident from the third day of hypoxia, and a steady state of hemoglobin concentration is reached within 11 days. The changes of hemoglobin subunit expression in response to hypoxia form the structural basis for the observed adjustments of hemoglobin function leading to enhanced oxygen transport at low ambient oxygen concentrations.

Simulation of fish behavior and mortality in hypoxic water in an enclosed bay

A model of fish preference for environmental conditions (dissolved oxygen (DO) and water temperature) and mortality was developed and coded within a combined hydrothermal and eutrophication model. The model was applied to an enclosed bay located in the western part of Japan, where eutrophication and associated onset of hypoxia at the bottom waters would occur in every summer. A field survey of fish behavior under hypoxic and non-hypoxic waters was conducted by releasing marbled sale in the bay and tracked its movement. At the same time, vertical profiles of DO, salinity and water temperature were measured at every 0.5m vertical interval at several locations along the tracking path of fish. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. The model could simulate reasonably the observed behavior and movement of the fish under both hypoxic and non-hypoxic waters in the bay; thereby, validated its applicability. Using the model, an assessment of the impact of the ongoing land reclamation project of about 400 ha in the bay on the fisheries resources was also conducted. The results showed that a substantial mortality of the fisheries resources would take place when hypoxic condition occurs in every summer and the construction of the artificial land will lower the mortality rate of fish during the summer period in the bay. Strong offshore winds cause the upwelling of bottom hypoxic waters in summer and the initial mortality of the fisheries resources increase under northerly offshore wind of 5 m/s or more.

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Hypoxic condition interferes with phosphorylation of Akt at Thr 308 in cultured rat pheochromocytoma-12 cells

Phosphorylation of Akt induced under hypoxic or ischemic conditions has been reported only for residue Ser 473. We examined whether Akt can be phosphorylated at Thr 308, another phosphorylation site on Akt, and can exhibit neuroprotective effects under conditions of hypoxia /reoxygenation, comparing pheochromocytoma-12 (PC12) cells transfected with constitutively active Akt (Myr-pCMV cells) and those transfected with pCMV vector only (pCMV cells). Expression levels of Akt phosphorylated at Ser 473 were 2.1-fold higher in Myr-pCMV cells compared with pCMV cells, before the onset of hypoxia, which were increased transiently during hypoxia, and then decreased gradually during reoxygenation. In contrast, Akt phosphorylated at Thr 308 was not detected in pCMV cells under any conditions but was expressed in Myr-pCMV cells prior to hypoxia, followed by an immediate decrease during hypoxia and a further decline during reoxygenation. However, G1-arrest of the cell cycle observed at 12 h after hypoxia in pCMV cells was prevented in Myr-pCMV cells. These findings suggest that hypoxia activates Akt by phosphorylation at Ser 473 only, which is sufficient to elicit a neuroprotective function against hypoxic neuronal damage.

Sudden infant death syndrome--a defect in circulatory control?

The majority of Sudden Infant Death Syndrome (SIDS) infants die during sleep and especially during the overnight sleep period. Recent evidence from SIDS cases, which occurred while on a cardiorespiratory monitor at home, has suggested that the mechanism of death involves circulatory failure, with the development of a shock like state, associated with a progressive bradycardia in the presence of continued breathing movements. In this paper we explore the circulatory effects of sleep and in particular the down regulation of the baroreceptor reflex, associated with a reduction in vasomotor tone and a fall in central venous return, cardiac output and blood pressure. This sequence of events would be exacerbated by many of the known SIDS risk factors, namely the prone sleeping position, overheating and co-sleeping. Poor central venous return,with diminished cardic distension could induce a progressive bradycardia as occurs in adults with neuro-cardiogenic syncope. Alternatively a reduced cardiac output could result in the rapid onset of severe hypoxia through poor lung perfusion. The effects of sleep on circulatory control deserve further study in infants.

Moderate hypoglycemia aggravates effects of hypoxia in hippocampal slices from diabetic rats

We recorded the effects of hypoxia combined with relative hypoglycemia on pre- and post-synaptic potentials in the CA1 area of slices from 4-month-old control and diabetic (streptozotocin-treated) Wistar rats. In experiments on slices kept in 10 or 4 mM glucose (at 33°C), hypoxia was applied until the pre-synaptic afferent volley disappeared – after 12–13 min in most slices, but much earlier (5±0.8 min) in diabetic slices kept in 4 mM glucose. When oxygenation was resumed, the afferent volley returned in all slices, for an overall mean recovery of 86.5% (±8.8%). Field post-synaptic potentials were fully blocked within 2–3 min of the onset of hypoxia. After the end of hypoxia, they failed to reappear in some slices: overall, their recovery varied between 62 and 68% in control slices, as well as in diabetic slices kept in 10 mM glucose; but recovery was very poor in diabetic slices kept in 4 mM glucose (only 15±0.94%). In the latter, hypoxic injury discharges occurred earlier (4.2±0.68 min vs. 6.5–8 min for other groups). We conclude that diabetes appears to make hippocampal slices more prone to irreversible loss of synaptic function and early block of axonal conduction when temporary hypoxia is combined with moderate hypoglycemia.

Molecular identification of O2 sensors and O2-sensitive potassium channels in the pulmonary circulation.

Small, muscular pulmonary arteries (PAs) constrict within seconds of the onset of alveolar hypoxia, diverting blood flow to better-ventilated lobes, thereby matching ventilation to perfusion and optimizing systemic PO2. This hypoxic pulmonary vasoconstriction (HPV) is enhanced by endothelial derived vasoconstrictors, such as endothelin, and inhibited by endothelial derived nitric oxide. However, the essence of the response is intrinsic to PA smooth muscle cells in resistance arteries (PASMCs). HPV is initiated by inhibition of the Kv channels in PASMCs which set the membrane potential (EM). It is currently uncertain whether this reflects an initial inhibitory effect of hypoxia on the K+ channels or an initial release of intracellular Ca2+, which then inhibits K+ channels. In either scenario, the resulting depolarization activates L-type, voltage gated Ca2+ channels, which raises cytosolic calcium levels [Ca2+]i and causes vasoconstriction. Nine families of Kv channels are recognized from cloning studies (Kv1-Kv9), each with subtypes (i.e. Kv1.1-1.6). The contribution of an individual Kv channel to the whole-cell current (IK) is difficult to determine pharmacologically because Kv channel inhibitors are nonspecific. Furthermore, the PASMC's IK is an ensemble, reflecting activity of several channels. The K+ channels which set EM, and inhibition of which initiates HPV, conduct an outward current which is slowly inactivating, and which is blocked by the Kv inhibitor 4-aminopyridine (4-AP) but not by inhibitors of Ca(2+)- or ATP-sensitive K+ channels. Using anti-Kv antibodies to immunolocalize and inhibit Kv channels, we showed that the PASMC contains numerous types of Kv channels from the Kv1 and Kv2 families., Furthermore Kv1.5 and Kv2.1 may be important in determining the EM and play a role as effectors of HPV in PASMCs. While the Kv channels in PASMCs are the "effectors" of HPV, it is uncertain whether they are intrinsically O2-sensitive or are under the control of an "O2 sensor". Certain Kv channels are rich in cysteine, and respond to the local redox environment, tending to open when oxidized and close when reduced. Candidate sensors vary the PASMC redox potential in proportion to O2. These include Nicotinamide Adenine Dinucleotide Phosphate Oxidase, (NADPH oxidase) and the cytosolic ratio of reduced/oxidized redox couples (i.e. glutathione GSH/GSSG), as controlled by electron flux in the mitochondrial electron transport chain (ETC). Using a mouse that lacks the gp91phox component of NADPH oxidase, we have recently shown that loss of the gp91phox-containing NADPH oxidase as a source of activated oxygen species does not impair HPV. However, inhibition of complex 1 of the mitochondrial electron transport chain mimics hypoxia in that it inhibits IK, reduces the production of activated O2 species and causes vasoconstriction. We hypothesize that a redox O2 sensor, perhaps in the mitochondrion, senses O2 through changes in the accumulation of freely diffusible electron donors. Changes in the ratio of reduced/oxidized redox couples, such as NADH/NAD+ and glutathione (GSH/GSSG) can reduce or oxidize the K+ channels, resulting in alterations of PA tone.

Enhanced Spontaneous Transmitter Release Is the Earliest Consequence of Neocortical Hypoxia That Can Explain the Disruption of Normal Circuit Function

After the onset of an acute episode of arrested circulation to the brain and consequent cerebral hypoxia, EEG changes and modifications of consciousness ensue within seconds. This in part reflects the rapid effect of hypoxia on the neocortex, where oxygen deprivation leads to impaired neuronal excitability and abnormal synaptic transmission. To identify the cellular mechanisms responsible for the earliest changes in neocortical function and to determine their time course, we have used patch-in-slice recording techniques to investigate the effects of acute hypoxia on the synaptic and intrinsic properties of layer 5 neurons. Coronal slices of mouse somatosensory cortex were maintained at 37 degrees C and challenged with episodes of hypoxia (3-4 min of exposure to 95% N(2), 5% CO(2)). In recordings with cell-attached patch electrodes, activation of ATP-sensitive potassium channels first became detectable 211 +/- 11 sec (range, 185-240 sec; n = 6 patches) after the onset of hypoxia. Similar recording techniques revealed no alterations in the properties of Na(+) currents in the first 4 min after the onset of hypoxia. The earliest hypoxia-induced disturbance was a marked increase in the frequency of spontaneous EPSCs and IPSCs, which began within 15-30 sec of the removal of oxygen. This rapid synaptic effect was not sensitive to TTX and was present in Ca(2+)-free perfusate, indicating that the hypoxia had a direct influence on the vesicular release mechanisms. The incoherent, massive increase in miniature PSCs would be expected to deplete the readily releasable pool of vesicles in cortical terminals, and to thereby markedly distort the neuronal interactions that underlie normal circuit function.

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.

Increased urinary flow without development of polyhydramnios in response to prolonged hypoxia in the ovine fetus

Objective: In the ovine fetus subjected to 24 hours of hypoxia, urinary flow is normal within a few hours from the onset of hypoxia and there is a maintained inhibition of swallowing. We hypothesized that 4 days of fetal hypoxia would lead to polyhydramnios. Study Design: Five late-gestation fetal sheep were subjected to hypoxia for 4 days and 7 other late-gestation fetal sheep served as time control animals. Fetal hypoxia was produced on postsurgical days 5 through 9 by continuous intratracheal nitrogen insufflation to the ewe. On days 3, 5, 7, and 9 after surgery, amniotic fluid volume, fetal urinary flow rate, and the compositions of maternal and fetal blood, amniotic fluid, and fetal urine were measured. A 3-factor analysis of variance was used for statistical analysis. Results: During the period of experimental hypoxia the mean (±SE) fetal PaO2 was 16.0 ± 0.6 mm Hg, versus 21.2 ± 0.7 mm Hg in control sheep (P <.001). Fetal hypoxia was associated with increased urinary flow on days 7 and 9, averaging 1410 ± 310 and 2101 ± 345 mL/d, respectively, versus 585 ± 92 and 699 ± 78 mL/d, respectively, in control animals (P <.001). Amniotic fluid volume was unchanged with time and averaged 960 ± 159 mL in hypoxic fetuses on postsurgical days 7 through 9 and 851 ± 130 mL in control animals (P =.60). Fetal blood lactate increased in the hypoxic animals, averaging 3.4 ± 2.1 mmol/L versus 1.6 ± 0.3 mmol/L in control animals (P =.02). Fetal urinary excretions of sodium, potassium, chloride, and lactate increased significantly during hypoxia, by 170% to 400%. Conclusion: Four days of nitrogen-induced hypoxia in the ovine fetus resulted in excess fetal urinary flow approximating 1000 mL/d greater than normal without the development of polyhydramnios. Because amniotic fluid volume did not change and hypoxia is a known inhibitor of fetal swallowing, we speculate that intramembranous absorption of amniotic water, electrolytes, and lactate increased. (Am J Obstet Gynecol 2001;184:1008-14.)

24 hour-CTG monitoring: comparison of normal pregnancies and pregnancies with placenta insufficiency.

Routinely antepartal CTG will be recorded for 30 minutes to obtain normal resting phases, a decrease of irregulatory due to hypoxia or to differentiate these from each other. In case of early onset of hypoxia first pathological findings might only be seen by chance in incidentally recorded CTG. The goal of this study was, if a continuous 24 hour-CTG will allow an earlier detection of beginning hypoxia in case of placental insufficiency compared to a routine CTG of 30 minutes. 21 normal pregnancies and 17 patients with placental insufficiency of > or = 36 weeks had 24 hour-CTG's by means of telemetry. In both study groups fetal heart rate (FHR) tracing included a full qualitative and quantitative description. Comparison of the results of both groups was done to look for early signs of pathological findings concerning reduced fetal well-being. In comparison to normal pregnancies patients with placental insufficiency had in 4.5% oscillation frequency type A and an increase of saltatory and silent oscillation. The number of accelerations and Dip 0 was significantly reduced as well as accelerations in combination with undulatory oscillation. Baseline tachycardia and bradycardia showed significantly increasing quantity. 24 hour-CTG is a good screening method to detect early onset of hypoxia in case of beginning placental insufficiency. The failure to find any clinically significant difference in the diurnal variation of both groups suggests, that less than 24 hour testing is required. 8 hour-CTG could be a compromise and a big help to detect a fetus at risk earlier.

Prenatal nicotine exposure increases apnoea and attenuates nicotinic potentiation of hypoglossal output in mice

Maternal smoking is associated with an increased risk of Sudden Infant Death Syndrome (SIDS) and nicotine is implicated as a causative agent due to adverse effects on central nervous system development [1]. The consequences of these changes for respiration are uncertain, but there is growing consensus that altered respiratory control contributes to the reduced ability of nicotine-exposed animals to tolerate hypoxia [2,3]. Most studies have focussed on overall changes in ventilation, but paid minimal attention to breathing pattern. In addition, responses have rarely been examined in the earliest neonatal periods when immature control mechanisms are more likely to contribute to unstable breathing, frequent apnoeas and hypoxic episodes. We therefore examined the effects of prenatal nicotine exposure on the development of breathing pattern and the ventilatory response to hypoxia (7.4% O2) in vivo using whole-body plethysmography at postnatal days 0, P3, P9, P19 and adult. To determine whether differences observed in vivo were due to altered activity of medullary respiratory networks, motoneurons (MNs) controlling the airway, or MN responsive-ness to nicotinic modulation, we recorded in vitro hypoglossal (XII) nerve and MN activity in rhythmic medullary slice preparations from control and nicotine-exposed P3 mice. Foetal mice were exposed to nicotine using osmotic micropumps implanted in the dam at gestational day 10. Developmental changes in respiratory behaviour in vivo were delayed in the youngest nicotine-exposed animals. The high level of apnoea present during normoxia in P0 control animals (frequency of apnoea, fA, 6.7 ± 0.7 min-1, percent of time apnoeic, TA, 29 ± 6%) and nicotine-exposed groups (fA 8.1 ± 1.7 min-1,TA 25 ± 5%) persisted until P3 in the nicotine group but fell significantly in control animals (fA-2.2 ± 0.7 min-1, TA 5 ± 2%). At the onset of hypoxia, fA and TA fell rapidly and remained low throughout hypoxia except in P0 nicotine-exposed animals where they declined initially (fA 1.8 ± 0.5, TA 4 ± 2%) but then rose progressively during the 12 min hypoxic period to final values of 7.1 ± 2.9 min-1and 17 ± 6% respectively. During recovery, apnoea increased in both groups at P0 (fA 10.8 ± 0.8 and 11.3 ± 1.3 min -1; TA 50 ± 6 and 49 ± 5%). By P3, the absolute magnitude of this posthypoxic increase was reduced in control (fA 5.3 ± 0.1 min-1 ; TA 30 ± 7%) but not nicotine-exposed animals (fA 8.5 ± 1.0 min-1 ; T 44 ± 8%). The frequency and variability of the inspiratory-related output in medullary slice preparations from control and nicotine-exposed animals were indistinguishable. The pattern of the inspiratory-related XII nerve burst and inspiratory synaptic currents recorded from XII MNs were also similar. Local application of nicotine (10–100 μM) over the XII nucleus produced a small, TTX-resistant inward current in MNs that reversed near 0 mV, and potentiated XII nerve inspiratory burst amplitude (25 ± 5%). Both actions were hexamethonium-sensitive, suggesting nicotinic receptor involvement in upper airway control. This potentiation was significantly lower in nicotine-exposed animals (14 ± 3%). Results indicate that prenatal nicotine exposure in mice delays development of breathing pattern, increasing incidence of apnoea in P0–P3 animals before, during and after hypoxia. This increased apnoea does not reflect alterations in the baseline behaviour of rhythm generating or pattern forming circuits, but may result from reduced nicotinic modulation of XII MN activity.

Hypoxia-induced Haem Oxygenase-1 gene expression in neonatal rat cardiac myocytes

Background: Haem oxygenase (HO-1), a heat shock or stress protein, is a rate-limiting enzyme in the conversion of pro-oxidant haem to biliverdin and carbon monoxide (CO). The products of haem catabolism serve regulatory and protective functions. Previous studies have shown that hypoxia induces HO-1 expression in cardiac myocytes. Accordingly, we investigated whether hypoxia-induced HO-1 expression is accompanied by increased CO production in cultured neonatal rat cardiac myocytes, and whether protein kinase C (PKC) is involved in hypoxia induced HO-1 gene expression. Methods and Results: Expression of HO-1 in hypoxia-treated cells was examined by using northern and western blotting, and immunofluorescent staining. The level of HO-1 mRNA at 24 and 48 h was increased after the onset of hypoxia, with corresponding increase in the HO-1 protein level (6.7- and 8.7-fold at 24 and 48 h of hypoxia, respectively). HO-1 protein was colocalised with sarcomeric α-actin in hypoxic myocytes. Hypoxia also significantly increased the production of CO by 2.5- and 8-fold at 24 and 48 h, respectively. Under normoxic conditions, activation of PKC by phorbol-12-myristate-13-acetate (PMA; 100 nmol/L) markedly increased HO-1 gene expression, while inhibition of PKC activity by calphostin C (100 nmol/L) blocked hypoxia-induced HO-1 gene expression in cardiac myocytes. Conclusions: These results demonstrate that hypoxia markedly induces HO-1 expression and increases the production of CO in cardiac myocytes. This hypoxic response is attributed, at least in part, to activation of PKC. Increased HO-1 expression and resultant CO production may be beneficial with respect to protection of cardiac myocytes under hypoxic conditions.