Exaggerated sympathetic mediated responses to behavioral or pharmacological challenges following antenatal betamethasone exposure

Glucocorticoid administration to women at risk for preterm delivery is standard practice to enhance neonatal survival. However, antenatal betamethasone exposure (β-exposure) increases mean arterial pressure (MAP) in adult sheep (1.8 yr old) and results in impaired baroreflex sensitivity (BRS) for control of heart rate (HR). In the current studies we tested the hypothesis that enhanced sympathetic nervous system and hypothalamo-pituitary-adrenal (HPA) axis-mediated responses are evident at an early age in β-exposed sheep. Pregnant ewes were administered betamethasone (0.17 mg/kg twice over 24 h) or vehicle (Veh-control) on the 80th day of gestation, and offspring were delivered at full term. Female β-exposed and control offspring instrumented at age 42 ± 3 days for conscious continuous recording of MAP and HR had similar resting values at baseline. However, BRS was ~45% lower in β-exposed offspring. β-Exposed lambs allowed to suckle for 10 min had a greater elevation in MAP than Veh-control lambs (19 ± 1 vs 12 ± 2 mmHg; n = 4-5, P < 0.05). MAP was reduced by 20% from baseline via sodium nitroprusside infusion (SNP) over 10 min, which triggered a rebound increase in MAP only in β-exposed lambs. HR increased with the reduction in MAP during SNP infusion in Veh-control lambs, whereas there was no change in HR with the reduction in MAP in β-exposed lambs. Combined vasopressin-CRF injection caused greater increases in MAP in the β-exposed lambs. Cortisol and ACTH responses were higher in response to SNP hypotension in the β-exposed lambs. The data reveal enhanced sympathetic and HPA axis responses associated with impaired BRS preceding differences in resting MAP in preweanling female lambs exposed in utero to glucocorticoids. The consequences of these alterations at an early age include eventual development of higher blood pressure in this ovine model of fetal programming.     

Maternal stress alters endocrine function of the feto-placental unit in rats

Prenatal stress (PS) can cause early and long-term developmental effects resulting in part from altered maternal and/or fetal glucocorticoid exposure. The aim of the present study was to assess the impact of chronic restraint stress during late gestation on feto-placental unit physiology and function in embryonic (E) day 21 male rat fetuses. Chronic stress decreased body weight gain and food intake of the dams and increased their adrenal weight. In the placenta of PS rats, the expression of glucose transporter type 1 (GLUT1) was decreased, whereas GLUT3 and GLUT4 were slightly increased. Moreover, placental expression and activity of the glucocorticoid "barrier" enzyme 11beta-hydroxysteroid dehydrogenase type 2 was strongly reduced. At E21, PS fetuses exhibited decreased body, adrenal pancreas, and testis weights. These alterations were associated with reduced pancreatic beta-cell mass, plasma levels of glucose, growth hormone, and ACTH, whereas corticosterone, insulin, IGF-1, and CBG levels were unaffected. These data emphasize the impact of PS on both fetal growth and endocrine function as well as on placental physiology, suggesting that PS could program processes implied in adult biology and pathophysiology.     

Intra-amniotic LPS and antenatal betamethasone: inflammation and maturation in preterm lamb lungs

The proinflammatory stimulus of chorioamnionitis is commonly associated with preterm delivery. Women at risk of preterm delivery receive antenatal glucocorticoids to functionally mature the fetal lung. However, the effects of the combined exposures of chorioamnionitis and antenatal glucocorticoids on the fetus are poorly understood. Time-mated ewes with singleton fetuses received an intra-amniotic injection of lipopolysaccharide (LPS) either preceding or following maternal intramuscular betamethasone 7 or 14 days before delivery, and the fetuses were delivered at 120 days gestational age (GA) (term = 150 days GA). Gestation matched controls received intra-amniotic and maternal intramuscular saline. Compared with saline controls, intra-amniotic LPS increased inflammatory cells in the bronchoalveolar lavage and myeloperoxidase, Toll-like receptor 2 and 4 mRNA, PU.1, CD3, and Foxp3-positive cells in the fetal lung. LPS-induced lung maturation measured as increased airway surfactant and improved lung gas volumes. Intra-amniotic LPS-induced inflammation persisted until 14 days after exposure. Betamethasone treatment alone induced modest lung maturation but, when administered before intra-amniotic LPS, suppressed lung inflammation. Interestingly, betamethasone treatment after LPS did not counteract inflammation but enhanced lung maturation. We conclude that the order of exposures of intra-amniotic LPS or maternal betamethasone had large effects on fetal lung inflammation and maturation.     

Lipid storage in cultured articular chondrocytes due to prostanoid precursors and a prostanoid synthesis inhibitor

Lapine articular chondrocytes were subcultured in the presence or absence of the prostanoid precursors, arachidonic acid or dihomo-gamma-linolenic acid, and the cyclooxygenase inhibitor indomethacin. Lipid storage was studied microscopically using the Sudan black staining method. Control chondrocyte cultures showed a weakly positive staining reaction until confluence was reached, at which point the intra-cytoplasmic lipid content decreased. Both arachidonic acid and dihomo-gamma-linolenic acid at 100 mumol/l caused a marked increase in lipid storage which continued even after confluence was achieved. 1 mumol/l concentrations were indistinguishable from controls, whereas 10 mumol/l concentrations elicited a slight increase in lipid storage compared with controls. The prostaglandin cyclooxygenase inhibitor indomethacin did not affect chondrocyte lipid storage. However, administration of a prostanoid precursor in the presence of indomethacin caused a massive increase in intra-cytoplasmic storage of lipid, eventually leading to cell death. A possible explanation is that indomethacin may alter chondrocyte lipid metabolism in the presence of substrate molecules by rechanneling lipid synthesis away from the prostaglandin pathway to other lipid synthetic pathways.     

Escherichia coli responses to a single DNA adduct

To study the mechanisms by which Escherichia coli modulates the genotoxic effects of DNA damage, a novel system has been developed which permits quantitative measurements of various E. coli pathways involved in mutagenesis and DNA repair. Events measured include fidelity and efficiency of translesion DNA synthesis, excision repair, and recombination repair. Our strategy involves heteroduplex plasmid DNA bearing a single site-specific DNA adduct and several mismatched regions. The plasmid replicates in a mismatch repair-deficient host with the mismatches serving as strand-specific markers. Analysis of progeny plasmid DNA for linkage of the strand-specific markers identifies the pathway from which the plasmid is derived. Using this approach, a single 1, N(6)-ethenodeoxyadenosine adduct was shown to be repaired inefficiently by excision repair, to inhibit DNA synthesis by approximately 80 to 90%, and to direct the incorporation of correct dTMP opposite this adduct. This approach is especially useful in analyzing the damage avoidance-tolerance mechanisms. Our results also show that (i) progeny derived from the damage avoidance-tolerance pathway(s) accounts for more than 15% of all progeny; (ii) this pathway(s) requires functional recA, recF, recO, and recR genes, suggesting the mechanism to be daughter strand gap repair; (iii) the ruvABC genes or the recG gene is also required; and (iv) the RecG pathway appears to be more active than the RuvABC pathway. Based on these results, the mechanism of the damage avoidance-tolerance pathway is discussed.     

Bleomycin-induced E prostanoid receptor changes alter fibroblast responses to prostaglandin E2

Although PGE(2) is a potent inhibitor of fibroblast function, PGE(2) levels are paradoxically elevated in murine lungs undergoing fibrotic responses. Pulmonary fibroblasts from untreated mice expressed all four E prostanoid (EP) receptors for PGE(2). However, following challenge with the fibrogenic agent, bleomycin, fibroblasts showed loss of EP2 expression. Lack of EP2 expression correlated with an inability of fibroblasts from bleomycin-treated mice to be inhibited by PGE(2) in assays of proliferation or collagen synthesis and blunted cAMP elevations in response to PGE(2). PGE(2) was similarly unable to suppress proliferation or collagen synthesis in fibroblasts from EP2(-/-) mice despite expression of the other EP receptors. EP2(-/-), but not EP1(-/-) or EP3(-/-) mice, showed exaggerated fibrotic responses to bleomycin administration in vivo as compared with wild-type controls. EP2 loss on fibroblasts was verified in a second model of pulmonary fibrosis using FITC. Our results for the first time link EP2 receptor loss on fibroblasts following fibrotic lung injury to altered suppression by PGE(2) and thus identify a novel fibrogenic mechanism.     

Unifying ecosystem responses to disturbance into a single statistical framework

Natural ecosystems are currently experiencing unprecedented rates of anthropogenic disturbance. Given the potential ramifications of more frequent disturbances, it is imperative that we accurately quantify ecosystem responses to severe disturbance. Specifically, ecologists and managers need estimates of resistance and recovery from disturbance that are free of observation error, not biased by temporal stochasticity and that standardize disturbance magnitude among many disparate ecosystems relative to normal interannual variability. Here, I propose a statistical framework that estimates all four components of ecosystem responses to disturbance (resistance, recovery, elasticity and return time), while resolving all of the issues described above. Coupling autoregressive time series with exogenous predictors (ARX) models with impulse response functions (IRFs) allows researchers to statistically subject all ecosystems to similar levels of disturbance, estimate lag effects and obtain standardized estimates of resistance to and recovery from disturbance that are free from observation error and stochastic processes inherent in raw data.     

Physiological responses of cotton to a single waterlogging at high and low N-levels

Surface-irrigated cotton (Gossypium hirsutum L.) grown on slowly draining clay soil is subjected to short-term periods of waterlogging at each irrigation which generally results in reduced productivity. The sequence of above- and below-ground plant responses to transient waterlogging and the role of N availability in modifying the immediate responses were studied. Lysimeters of Marah clay loam (a Natrustalf) were instrumented to monitor soil and plant responses to a 7-day waterlogging event beginning 67 days after sowing. Cotton (‘Deltapine 61’) plants (8 per lysimeter) were grown with two levels of added N (300 kg ha⁻¹ and 30 kg ha⁻¹) and two irrigation treatments (flooded and control). Measured soil-O₂ levels decreased rapidly upon surface flooding because water displaced air and root zone respiration consumed O₂. The rate of O₂ consumption was 2.7 times greater in the high-N treatment than the low-N treatment. This difference was associated with a 1.8 fold difference in numbers of observed roots. Root growth was only slightly affected by flooding. Leaf growth decreased by 28%, foliage temperature increased 2.3% and apparent photosynthesis decreased by 16%. It is suggested that flooding reduced photosynthetic activity within 2 days while other stress symptoms became apparent after about 6 days. Although this stress was reflected in a trend for decreased plant productivity, the effect of flooding on boll dry mass at harvest was not significant at the level of replication used. The single waterlogging did not cause yield reductions comparable to those observed elsewhere when several waterlogging events were imposed. Contribution from the CSIRO, Centre for Irrigation Research, Griffith, NSW, Australia and USDA-ARS, Morris, MI, USA, in cooperation with the univ. of Minnesota.     

Activation of the D prostanoid receptor 1 regulates immune and skin allergic responses

The mobilization of Langerhans cells (LCs) from epithelia to the draining lymph nodes is an essential process to initiate primary immune responses. We have recently shown that in mice, PGD2 is a potent inhibitor of epidermal LC emigration. In this study, we demonstrate that activation of the D prostanoid receptor 1 (DP1) impedes the TNF-alpha-induced migration of human LCs from skin explants and strongly inhibits the chemotactic responses of human LC precursors and of maturing LCs to CC chemokine ligands 20 and 19, respectively. Using a murine model of atopic dermatitis, a chronic Th2-type allergic inflammatory disease, we demonstrate that the potent DP1 agonist BW245C dramatically decreases the Ag-specific T cell activation in the skin draining lymph nodes and markedly prevents the skin lesions following repeated epicutaneous sensitization with OVA. Interestingly, analysis of the local response indicates that BW245C treatment strongly reduces the recruitment of inflammatory cells into the dermis and disrupts the Th1/Th2 balance, probably through the increased production of the immunoregulatory cytokine IL-10, in the skin of sensitized mice. Taken together, our results suggest a new function for DP1 in the regulation of the immune and inflammatory responses. We propose that DP1 activation by specific agonists may represent a strategy to control cutaneous inflammatory Th2-associated diseases.     

Maternal immune system adaptation to pregnancy - a potential influence on the course of diabetic retinopathy

Background  

Progression of diabetic retinopathy occurs at least temporarily during pregnancy. Although the cause of this progression is not entirely understood, the immune phenomenon and chronic inflammation may play a significant role. During pregnancy in order to avoid fetus rejection, certain components of the immune system that are knowingly implicated in the pathogenesis of diabetic retinopathy are activated including generalized leukocyte activation and an increase in certain cytokine plasma levels. Activated leukocytes with up regulated adhesion molecules have an increased potential to bind to the endothelium cells of blood vessels. Leukocyte-endothelial interaction and the consequent leukostasis with capillary occlusion, ischemia and vascular leakage have a substantial role in the development of diabetic retinopathy. Furthermore, certain increased cytokines are known to cause blood-retinal-barrier breakdown whilst others promote angiogenic and fibrovascular proliferation and thereby can also be implicated in the pathogenesis of this diabetic complication.     

Effect of thyroxine treatment on metabolic responses to a single insulin injection

Metabolic responses to a single i.v. injection of cristalline insulin (0.2 i.u./kg b.w.) were compared in control and T4-treated dogs both at rest and after prolonged physical exercise. The post-insulin decrease in blood glucose was significantly correlated with the pre-insulin BG concentration. Thus, the insulin-induced fall of BG was greatest in T4-treated dogs at rest, in which significantly higher BG levels were found in comparison with controls, and smallest in the same dogs after exercise, i.e. at the lowest initial BG concentrations. The post-insulin hypoglycaemia caused marked increases in the plasma FFA level in control dogs, both at rest and after physical effort, and in T4-treated dogs at rest. They were accompanied by elevations in the plasma adrenaline levels. In T4-treated dogs given insulin after exercise decreases both in the plasma FFA and A concentrations were found. In the majority of the control and T4-treated dogs insulin injected at rest caused an increase in blood LA levels, being more pronounced in the latter. Insulin injected after physical exercise did not change blood LA level in T4 treated dogs, and it caused its decrease in the control animals. The results of these investigations show that both T4-treatment and physical exercise, performed prior to insulin injection, modify the metabolic response to insulin and post-insulin hypoglycaemia.     

Maternal care and the development of stress responses

Studies dating from the 1950s have documented the impact of early life events on the development of behavioral and endocrine responses to stress. Recent findings suggest that these effects are mediated through changes in mother-offspring interactions and have identified central corticotropin-releasing factor systems as a critical target for the effects of variations in maternal care.     

Time course of antioxidant responses of Capsicum annuum subjected to a progressive magnesium deficiency

The effect of magnesium (Mg²⁺)‐deficiency on the antioxidant responses of Capsicum annuum was investigated over a 60‐day period under controlled conditions. This Mg²⁺‐deficiency aimed to mimic the physiological conditions that plants may experience in the field. At each harvest time, five different leaf‐levels (L2 to L6) were distinguished. L2 and L6 correspond to the second and sixth youngest leaves, respectively. The following parameters were determined: Mg²⁺, chlorophyll and protein contents, total and redox pools of ascorbate and glutathione, and the activities of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Under Mg²⁺‐deficiency, leaf Mg²⁺ contents decreased over time in all leaf‐levels except in the second youngest leaves (L2), where they remained constant at about 0.25% (dry weight basis). Mg²⁺‐deficiency led to an increase in the antioxidant enzyme activities concomitant with an increase in the ascorbate and glutathione pools, whereas total chlorophyll and soluble protein contents decreased. The L2 leaves showed an increase in glutathione reductase activity and in the ascorbate redox state whereas no difference was observed for the other parameters. Superoxide dismutase activities increased in L5 leaves from day 15 and, afterwards, in L3 to L5 leaves, irrespective of Mg²⁺ content. At day 30, glutathione reductase activities increased in L2 to L4 leaves and dehydroascorbate reductase activities in L4 leaves. At day 45, we observed an increase in the ascorbate peroxidase activities in L3 to L5 leaves. At the same time, ascorbate and glutathione pools increased in intermediate leaves, whereas chlorophyll content decreased in L3 and L4 leaves, and protein content decreased in L4 leaves. Results suggest that pepper leaves enhance their defence capacities against oxidative stress by increasing ascorbate more than glutathione synthesis. However, cells showed higher regeneration rates for the glutathione redox state than for the ascorbate redox state.     

Comparison of serum steroid responses to a single injection of hCG in man and rat

The responses of peripheral serum steroids to a single injection of hCG (80 IU/kg b wt) were compared in adult male rats and humans. Before hCG, the quantitatively dominating steroids were dehydroepiandrosterone, testosterone and 17-hydroxypregnenolone in the men, and testosterone and progesterone in the rats. One hour after hCG the concentrations of testosterone and all its precursors measured except for pregnenolone were significantly elevated in the rat serum, whereas a clear rapid response was not observed in the men. Transient blockade of C21 steroid side-chain cleavage was seen in both species at about 24-36 h after hCG, which occurred at the same time as the maximum concentration of estradiol in the men. No changes in rat serum estradiol concentrations were observed. Both species showed a secondary stimulation of testosterone and androstenedione formation at around 3 days. Our findings are compatible with the concept that the main difference in the gonadotropin-stimulated steroidogenesis in man and rat is the magnitude of the rapid steroidogenic response to hCG, which is very small in man and indicates smaller supply or lesser metabolism of mitochondrial cholesterol in human testis.