Response dynamics of entorhinal cortex in awake, anesthetized, and bulbotomized rats

The steady-state rate of glucose oxidation through the mitochondrial TCA cycle (V(TCA)) was measured in acid extracts of 10- and 30-day-old cerebral cortex of rats receiving [1-13C]glucose intravenously and in neocortical slices superfused in vitro with the same isotope. TCA cycle flux was determined for each age group based on metabolic modeling analysis of the isotopic turnover of cortical glutamate and lactate. The sensitivity of the calculated rates to assumed parameters in the model were also assessed. Between 10 and 30 postnatal days, V(TCA) increased by 4.3-fold (from 0.46 to 2.0 micromol g(-1) min(-1)) in the cortex in vivo, whereas only a 2-fold (from 0.17 to 0.34 micromol g(-1) min(-1)) increase was observed in neocortical slices. The much greater increase in glucose oxidative metabolism of the cortex measured in vivo over that measured in vitro as the cortex matures suggests that function-related energy demands increase during development, a process that is deficient in the slice as a result of deafferentiation and other mechanisms.     

Poorly controlled type 1 diabetes is associated with altered glutathione homeostasis in adolescents: apparent resistance to N‐acetylcysteine supplementation

Blood glutathione concentrations represent a measure of protection against oxidative damage. In earlier studies, we observed that, in adolescents with poorly controlled type 1 diabetes mellitus (T1DM), blood glutathione is significantly depleted because of increased rates of glutathione utilization. To determine whether increased availability of cysteine – one of the three constitutive amino acids of glutathione – would attenuate the alterations in glutathione metabolism, ten 16 ± 1 yr‐old adolescents with poorly controlled T1DM [hemoglobin A1c (HbA1c): 9.9 ± 1.3%] received 5‐h infusions of l ‐[3,3‐²H₂] cysteine and d ‐[6,6‐²H₂]glucose on two occasions, 3 wk apart, after a 10‐d oral supplementation with (i) N‐acetylcysteine (NAC, 30–45 mg/kg/d) or (ii) l ‐alanine, in randomized order, and with a 3‐wk ‘washout’ interim period. Blood glucose was maintained in the same hyperglycemic range on both infusion study days, using intravenous insulin. Glutathione fractional synthesis rate (FSR) was determined from ²H₂‐cysteine incorporation into blood glutathione. NAC supplementation failed to raise erythrocyte cysteine concentrations (23 ± 6 vs. 17 ± 1 μmol/L, p = 0.853) and did not alter erythrocyte glutathione concentrations (838 ± 106 vs. 793 ± 111 μmol/L, p = 0.220) or glutathione FSR (96 ± 20 vs. 89 ± 19%/d, p = 0.974). We conclude that in adolescents with poorly controlled T1DM, dietary cysteine supplementation alone cannot correct glutathione status. In the presence of relative insulinopenia, either higher amino acid doses or aggressive insulin therapy may be needed to achieve this goal. This would require further study.     

Use of stable48Ca in the clinical measurement of intestinal calcium absorption

Summary Measurements of intestinal-calcium-absorption efficiency are fundamental for understanding calcium homeostasis in health and disease. Stable calcium isotopes are attractive tracers for such measurements, to avoid excessive radiation exposure to the subject and permit serial studies at short intervals. To realize this, we found it necessary to improve the sensitivity and precision of existing thermal neutron activation analyses for⁴⁸Ca. This report describes the details, sensitivity, precision, and accuracy of the improved method, and gives the results of studies in which intravenous⁴⁸Ca was used in conjunction with oral⁴⁷Ca to measure intestinal-calcium-absorption efficiency in patients.     

A comparison of PET imaging characteristics of various copper radioisotopes

Purpose PET radiotracers which incorporate longer-lived radionuclides enable biological processes to be studied over many hours, at centres remote from a cyclotron. This paper examines the radioisotope characteristics, imaging performance, radiation dosimetry and production modes of the four copper radioisotopes, ⁶⁰Cu, ⁶¹Cu, ⁶²Cu and ⁶⁴Cu, to assess their merits for different PET imaging applications. Methods Spatial resolution, sensitivity, scatter fraction and noise-equivalent count rate (NEC) are predicted for ⁶⁰Cu, ⁶¹Cu, ⁶²Cu and ⁶⁴Cu using a model incorporating radionuclide decay properties and scanner parameters for the GE Advance scanner. Dosimetry for ⁶⁰Cu, ⁶¹Cu and ⁶⁴Cu is performed using the MIRD model and published biodistribution data for copper(II) pyruvaldehyde bis(N⁴-methyl)thiosemicarbazone (Cu-PTSM). Results ⁶⁰Cu and ⁶²Cu are characterised by shorter half-lives and higher sensitivity and NEC, making them more suitable for studying the faster kinetics of small molecules, such as Cu-PTSM. ⁶¹Cu and ⁶⁴Cu have longer half-lives, enabling studies of the slower kinetics of cells and peptides and prolonged imaging to compensate for lower sensitivity, together with better spatial resolution, which partially compensates for loss of image contrast. ⁶¹Cu-PTSM and ⁶⁴Cu-PTSM are associated with radiation doses similar to [¹⁸F]-fluorodeoxyglucose, whilst the doses for ⁶⁰Cu-PTSM and ⁶²Cu-PTSM are lower and more comparable with H₂¹⁵O. Conclusion The physical and radiochemical characteristics of the four copper isotopes make each more suited to some imaging tasks than others. The results presented here assist in selecting the preferred radioisotope for a given imaging application, and illustrate a strategy which can be extended to the majority of novel PET tracers.     

Sevoflurane versus isoflurane--anaesthesia for lower abdominal surgery. Effects on perioperative glucose metabolism

BACKGROUND: The aim of this study was to determine the impact of sevoflurane anaesthesia on metabolic and endocrine responses to lower abdominal surgery. METHODS: A prospective randomized controlled study in 20 patients undergoing abdominal hysterectomy. Patients were randomly assigned to receive either sevoflurane (S) or isoflurane anaesthesia (I). Using a stable isotope dilution technique, endogenous glucose production (EGP) and plasma glucose clearance (GC) were determined pre- and postoperatively (6,6-2H2-glucose). Plasma concentrations of glucose, insulin, cortisol, epinephrine and norepinephrine were measured preoperatively, 5 min after induction of anaesthesia, during surgery and 2 h after the operation. RESULTS: EGP increased in both groups with no intergroup differences (preop. S 12.2 +/- 1.6, I 12.4 +/- 1.6; postop. S 16.3 +/- 1.9*, I 19.0 +/- 3.1* micromol kg(-1) min(-1), all values are means +/- SD, *P < 0.05 vs. preop.). Plasma glucose concentration increased and GC decreased in both groups. There were no differences between groups. (Glucose conc. mmol l(-1) preop.: S 4.1 +/- 0.3, I 3.9 +/- 0.5; 5 AI S 5.1 +/- 0.6*, I 5.1 +/- 1.0*, postop. S 7.0 +/- 1.0*, I 7.1 +/- 1.4*; * = P < 0.05 vs. preop.; GC ml kg(-1)min(-1) preop. S 3.0 +/- 0.4, I 3.2 +/- 0.4; postop. S 2.4 +/- 0.3*, I 2.7 +/- 0.3*; *=P < 0.05 vs. preop.) Insulin plasma concentrations were unchanged. Cortisol plasma concentrations increased intra- and postoperatively with no changes between the groups. Norepinephrine plasma concentration increased in the S group after induction of anaesthesia. I group norepinephrine was increased 2 h after operation and showed no intergroup differences. CONCLUSION: Sevoflurane, as well as isoflurane, does not prevent the metabolic endocrine responses to surgery.     

From the Cover: Feature Article: Water,plants, and early human habitats in eastern Africa

Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa—Olduvai Gorge. We convert sedimentary leaf- and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water–lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lake-water δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C₄-dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm·y⁻¹ and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.     

DETERMINATIONS OF GLUCOSE TURNOVER AND OXIDATION IN NORMAL VOLUNTEERS AND SEPTIC PATIENTS USING STABLE AND RADIO-ISOTOPES

Rates of glucose turnover and oxidation were isotopically determined in normal volunteers (n= 16) and in severely septic patients (n= 10). Glucose turnover was determined using primed constant infusions of either 6-³H- or 6,6-d-glucose and glucose oxidation with either U-¹⁴C-glucose or U-¹³C-glucose after appropriate priming of the bicarbonate pool. Basal rates of glucose turnover, oxidation, and plasma clearance were significantly higher in the septic patients than in the volunteers. During glucose infusion (4 mg/kg·min) endogenous glucose production was virtually abolished in the volunteers (94±4% suppression). There was significantly less suppression in the septic patients (39±7%); (p<0.01). In addition, the percentage of available glucose oxidized (i.e. the percentage of glucose uptake oxidized) was significantly less in the septic patients. When the patients were studied during total parenteral nutrition (at a similar rate of glucose infusion) there was no further suppression of endogenous glucose production compared with that seen during 2h of glucose infusioin. However, the percentage of available glucose oxidized increased significantly. From these studies it is concluded that (i) septic patients continue to have ongoing consumption of host tissue despite receiving either glucose infusion or total parenteral nutrition, and (ii) septic patients are less able to oxidize glucose than normal volunteers when infused for only 2 h. However, adaptation occurs with the longer infusion time used in total parenteral nutrition (TPN).     

[13C]-Galactose breath test: correlation with liver fibrosis in chronic hepatitis C

BACKGROUND: The galactose elimination capacity test is a quantitative liver function test that has been shown to be a potential surrogate marker for death in advanced chronic liver diseases. However, this test lacks sensitivity in early liver disease. The goal of this study was to evaluate a [13C]-galactose breath test (GBT) in a population of patients with chronic hepatitis C. DESIGN: The GBT was performed in 10 control subjects and 50 patients with chronic hepatitis C; the results were compared with the METAVIR pathological scoring of liver biopsy specimens and with standard biochemical liver function tests. RESULTS: In 10 patients, oral vs. intravenous administration of galactose yielded similar results for the GBT (3.01% +/- 0.12% dose h-1 for oral galactose vs. 2.98 +/- 0.21 for intravenous). The GBT was then performed orally in the remaining 40 patients and 10 control subjects. A significant difference was observed between control subjects and patients (4.51% +/- 0.18% vs. 2.97% +/- 0.14% dose h-1, P < 0.0001). A significant difference for GBT results was observed between each fibrosis stage, but not with regard to the activity score. CONCLUSIONS: The GBT results are dependent on the severity of liver fibrosis in chronic hepatitis C. Further studies are needed to evaluate the usefulness of the GBT for the follow-up of chronic hepatitis C.     

A CO2 greenhouse efficiently warmed the early Earth and decreased seawater 18O/16O before the onset of plate tectonics

The low ¹⁸O/¹⁶O stable isotope ratios (δ¹⁸O) of ancient chemical sediments imply ∼70 °C Archean oceans if the oxygen isotopic composition of seawater (sw) was similar to modern values. Models suggesting lower δ¹⁸O_sw of Archean seawater due to intense continental weathering and/or low degrees of hydrothermal alteration are inconsistent with the triple oxygen isotope composition (Δ’¹⁷O) of Precambrian cherts. We show that high CO₂ sequestration fluxes into the oceanic crust, associated with extensive silicification, lowered the δ¹⁸O_sw of seawater on the early Earth without affecting the Δ’¹⁷O. Hence, the controversial long-term trend of increasing δ¹⁸O in chemical sediments over Earth’s history partly reflects increasing δ¹⁸O_sw due to decreasing atmospheric pCO₂. We suggest that δ¹⁸O_sw increased from about −5‰ at 3.2 Ga to a new steady-state value close to −2‰ at 2.6 Ga, coinciding with a profound drop in pCO₂ that has been suggested for this time interval. Using the moderately low δ¹⁸O_sw values, a warm but not hot climate can be inferred from the δ¹⁸O of the most pristine chemical sediments. Our results are most consistent with a model in which the “faint young Sun” was efficiently counterbalanced by a high-pCO₂ greenhouse atmosphere before 3 Ga.

The amount of carbon that degassed from a solidifying magma ocean on the infant Earth 4.5 Ga ago was probably similar to the amount of CO₂ that is now present in the atmosphere of Venus (pCO₂ ∼90 bar) (1). Subsequently, dynamic carbon cycling between the early Earth’s atmosphere (atmospheric reservoir [R_A]), the ocean (R_O), and the oceanic crust (R_OC) reservoirs stabilized a primordial Earth–atmospheric pCO₂ to about 1.5 bar (2). Decreasing pCO₂ over the Earth’s history reflects the net transfer of large masses of carbon out of the atmosphere-ocean-oceanic crust (R_A+O+OC) system into the mantle and the emerging continental crust reservoir (R_CC), the latter providing a long-term sink for carbon in the form of inorganic carbon (carbonate rocks) and organic material (organic matter–rich shales, coal, oil, and gas) (1, 2).Early carbon-cycle models predicted high Archean pCO₂ to account for the faint young Sun paradox (2, 3), whereas direct pCO₂ estimates from the end of the Archean now imply much lower atmospheric pCO₂ [∼0.01 to 0.1 bar (4)]. However, a compilation of evidence from the sedimentary record implies much higher pCO₂ between 3.2 to 3.0 Ga compared to the 2.9 to 2.7 Ga interval (5). These authors state that even several bars pCO₂ are feasible between 3.2 to 3.0 Ga, which is not in conflict with much lower Neoarchean pCO₂ estimates (Fig. 1) or paleo-atmospheric pressure estimates at 2.7 Ga [<2 bar (6) and <0.5 bar (7)]. A fundamental drop in atmospheric CO₂ mixing ratio is also reflected in the observation that >3 Ga, Archean mafic crust (greenstones) is commonly characterized by very intense carbonatization and silicification that is unparalleled in their modern analogs (8–12). Such observations provide evidence for deep-time paleo-pCO₂ fluctuations with a drastic pCO₂ drop starting around 3 Ga ago (5, 13).Open in a separate windowFig. 1.Constraints on the R_A+O+OC size over time with implications for pCO₂. A illustrates the size of the R_A+O+OC carbon reservoir and its distribution between the oceanic crust (R_OC in gray), ocean water (R_O in dark blue), and the atmosphere (R_A in light blue). Transition of this carbon to the long-term R_CC and the mantle (green) decreases the size of the R_A+O+OC reservoir, which was still large at 3.2 Ga (see SI Appendix) and minimal at the onset of the global glaciations at 2.4 Ga. B shows two recent pH curves over Earth’s history to illustrate how the pH-dependent distribution of carbon between R_A and R_O may translate into pCO₂ at a given time. (C) The panel summarizes pCO₂ estimates [adopted from Catling and Zahnle (4)] and proposed pCO₂ evolution curves illustrated as dashed lines: a (2), b (18), and c (proposed here). Qualitative evidence to construct curve c comes from rare evidence for glaciers (44) and lower degrees of carbonatization of oceanic crust at 3.5 Ga compared to 3.2 Ga (13), suggesting a transient interval of somewhat low pCO₂ in the Paleoarchean. Low pCO₂ is indicated prior to the onset of cold climates later in the rock record. The black bar at 4.5 Ga is derived from carbon-flux arguments and the primordial carbon reservoir (1, 2). The black bar at 3.2 Ga applies the same carbon-flux arguments to translate the high carbonate content observed in the oceanic crust in Pilbara into tentative pCO₂ estimates (SI Appendix), which are most consistent with curve a (2).Today, carbonatization, which is the formation of carbonates during alteration of the oceanic crust, mainly occurs in relatively cool, off-axis hydrothermal systems over the first 20 Mya after crust formation at midocean ridges (14–16). Elevated degrees of carbonatization in oceanic crust from the Cretaceous and Jurassic are assigned to higher dissolved inorganic carbon at the time (14). Hence, higher pCO₂ (i.e., a larger R_A+O+OC) directly translates into higher degrees of carbonatization. While carbonate is mainly observed as vein fillings in the upper 300 m of oceanic crust today (14, 15), it extensively replaces glass and igneous minerals in Archean greenstones down to depths of 2 km below the ancient seafloor (8–10, 17). The amount of CO₂ fixed in 3.2-Ga-old oceanic crust from Pilbara, Australia is estimated at 1.2 × 10⁷ mol ⋅ m⁻² (±10%) (17)—a remarkable figure that is about two orders of magnitude more compared to today (SI Appendix). Much lower degrees of carbonatization in oceanic crust are already observed at 2.6 Ga, suggesting a drastic Mesoarchean drop in pCO₂ (13) (Fig. 1A).The qualitative evidence from the sediment record (5) and from the degree of carbonatization and silicification of oceanic crust (13) has not been included in proposed pCO₂ curves (4, 18) because the quantitative conversions into absolute pCO₂ require some assumptions (SI Appendix). Nevertheless, pCO₂ during the early Archean may have been as high as initially predicted by Kasting (2), followed by a pronounced Mesoarchean drop (13) to levels consistent with available paleo-pCO₂ estimates toward the Neoarchean (4) (stippled line “c” in Fig. 1C). Further decreasing pCO₂ toward modern levels partly reflects increasing ocean pH (Fig. 1) rather than a shrinking R_A+O+OC (SI Appendix). Hence, only small effects of carbonatization on the δ¹⁸O_sw value are expected for post-Archean seawater (16). Here, we focus on the very high carbonatization (8–10, 13) and silicification (11, 12) fluxes before the Mesoarchean pCO₂ drop, and we model the respective effects on ancient δ¹⁸O_sw.