High fat-diet and saturated fatty acid palmitate inhibits IGF-1 function in chondrocytes.

INTRODUCTION: Insulin-like growth factor-1 (IGF-1) promotes matrix synthesis and cell survival in cartilage. Chondrocytes from aged and osteoarthritic cartilage have a reduced response to IGF-1. The purpose of this study was to determine the effect of free fatty acids (FFA) present in a high-fat diet on IGF-1 function in cartilage and the role of endoplasmic reticulum (ER) stress. METHODS: C57BL/6 male mice were maintained on either a high-fat (60% kcal from fat) or a low-fat (10% kcal from fat) diet for 4 months. Mice were then sacrificed; femoral head cartilage caps were collected and treated with IGF-1 to measure proteoglycan (PG) synthesis. Cultured human chondrocytes were treated with 500 µM FFA palmitate or oleate, followed by stimulation with (100 ng/ml) IGF-1 overnight to measure CHOP (a protein marker for ER stress) and PG synthesis. Human chondrocytes were pre-treated with palmitate or 1 mM 4-phenyl butyric acid (PBA) or 1 µM C-Jun N terminal Kinase (JNK) inhibitor, and IGF-1 function (PG synthesis and signaling) was measured. RESULTS: Cartilage explants from mice on the high fat-diet showed reduced IGF-1 mediated PG synthesis compared to a low-fat group. Treatment of human chondrocytes with palmitate induced expression of CHOP, activated JNK and inhibited IGF-1 function. PBA, a small molecule chemical chaperone that alleviates ER stress rescued IGF-1 function and a JNK inhibitor rescued IGF-1 signaling. CONCLUSIONS: Palmitate-induced ER stress inhibited IGF-1 function in chondrocytes/cartilage via activating the mitogen-activated protein (MAP) kinase JNK. This is the first study to demonstrate that ER stress is metabolic factor that regulates IGF-1 function in chondrocytes.

Spaceflight-Relevant Challenges of Radiation and/or Reduced Weight Bearing Cause Arthritic Responses in Knee Articular Cartilage.

There is little known about the effect of both reduced weight bearing and exposure to radiation during spaceflight on the mechanically-sensitive cartilage lining the knee joint. In this study, we characterized cartilage damage in rat knees after periods of reduced weight bearing with/without exposure to solar-flare-relevant radiation, then cartilage recovery after return to weight bearing. Male Sprague Dawley rats (n = 120) were either hindlimb unloaded (HLU) via tail suspension or remained weight bearing in cages (GROUND). On day 5, half of the HLU and GROUND rats were 1 Gy total-body X-ray irradiated during HLU, and half were sham irradiated (SHAM), yielding 4 groups: GROUND-SHAM; GROUND-IR; HLU-SHAM; and HLU-IR. Hindlimbs were collected from half of each group of rats on day 13. The remaining rats were then removed from HLU or remained weight bearing, and hindlimbs from these rats were collected on day 62. On day 13, glycosaminoglycan (GAG) content in cartilage lining the tibial plateau and femoral condyles of HLU rats was lower than that of the GROUND animals. Likewise, on day 13, immunoreactivity of the collagen type II-degrading matrix metalloproteinase-13 (MMP-13) and of a resultant metalloproteinase-generated neoepitope VDIPEN was increased in all groups versus GROUND-SHAM. Clustering of chondrocytes indicating cartilage damage was present in all HLU and IR groups versus GROUND-SHAM on day 13. On day 62, after 49 days of reloading, the loss of GAG content was attenuated in the HLU-SHAM and HLU-IR groups, and the increased VDIPEN staining in all treatment groups was attenuated. However, the increased chondrocyte clustering remained in all treatment groups on day 62. MMP-13 activity also remained elevated in the GROUND-IR and HLU-IR groups. Increased T2 relaxation times, measured on day 62 using 7T MRI, were greater in GROUND-IR and HLU-IR knees, indicating persistent cartilage damage in the irradiated groups. Both HLU and total-body irradiation resulted in acute degenerative and pre-arthritic changes in the knee articular cartilage of rats. A return to normal weight bearing resulted in some recovery from cartilage degradation. However, radiation delivered as both a single challenge and when combined with HLU resulted in chronic cartilage damage. These findings suggest that radiation exposure during spaceflight leads to and/or impairs recovery of cartilage upon return to reloading, generating long-term joint problems for astronauts.

Lung cancer risk test trial: study design, participant baseline characteristics, bronchoscopy safety, and establishment of a biospecimen repository.

BACKGROUND: The Lung Cancer Risk Test (LCRT) trial is a prospective cohort study comparing lung cancer incidence among persons with a positive or negative value for the LCRT, a 15 gene test measured in normal bronchial epithelial cells (NBEC). The purpose of this article is to describe the study design, primary endpoint, and safety; baseline characteristics of enrolled individuals; and establishment of a bio-specimen repository. METHODS/DESIGN: Eligible participants were aged 50-90 years, current or former smokers with 20 pack-years or more cigarette smoking history, free of lung cancer, and willing to undergo bronchoscopic brush biopsy for NBEC sample collection. NBEC, peripheral blood samples, baseline CT, and medical and demographic data were collected from each subject. DISCUSSION: Over a two-year span (2010-2012), 403 subjects were enrolled at 12 sites. At baseline 384 subjects remained in study and mean age and smoking history were 62.9 years and 50.4 pack-years respectively, with 34% current smokers. Obstructive lung disease (FEV1/FVC <0.7) was present in 157 (54%). No severe adverse events were associated with bronchoscopic brushing. An NBEC and matched peripheral blood bio-specimen repository was established. The demographic composition of the enrolled group is representative of the population for which the LCRT is intended. Specifically, based on baseline population characteristics we expect lung cancer incidence in this cohort to be representative of the population eligible for low-dose Computed Tomography (LDCT) lung cancer screening. Collection of NBEC by bronchial brush biopsy/bronchoscopy was safe and well-tolerated in this population. These findings support the feasibility of testing LCRT clinical utility in this prospective study. If validated, the LCRT has the potential to significantly narrow the population of individuals requiring annual low-dose helical CT screening for early detection of lung cancer and delay the onset of screening for individuals with results indicating low lung cancer risk. For these individuals, the small risk incurred by undergoing once in a lifetime bronchoscopic sample collection for LCRT may be offset by a reduction in their CT-related risks. The LCRT biospecimen repository will enable additional studies of genetic basis for COPD and/or lung cancer risk. TRIAL REGISTRATION: The LCRT Study, NCT 01130285, was registered with Clinicaltrials.gov on May 24, 2010.

Osteoarthritic changes in vervet monkey knees correlate with meniscus degradation and increased matrix metalloproteinase and cytokine secretion.

OBJECTIVE: Meniscus injury increases osteoarthritis risk but its pathobiology in osteoarthritis is unclear. We hypothesized that older adult vervet monkeys would exhibit knee osteoarthritic changes and the degenerative menisci from these animals would secrete matrix metalloproteinases (MMPs) and pro-inflammatory cytokines that contribute to the development of osteoarthritis. DESIGN: In a cross sectional analysis of healthy young adult (9-12 years) and old (19-26 years) adult female vervet monkeys, knees were evaluated in vivo with computed tomography (CT) imaging, and joint tissues were morphologically graded at necropsy. Meniscus explants were subsequently cultured to evaluate meniscal MMP and cytokine secretion. RESULTS: CT images revealed significant bony osteoarthritic changes in 80% of older monkeys which included increases in osteophyte number and meniscal calcification. Meniscus and cartilage degradation scores were greater in the older monkeys and were positively correlated (r > 0.7). Menisci from older animals exhibiting osteoarthritic changes secreted significantly more MMP-1, MMP-3, and MMP-8 than healthy menisci from younger monkeys. Older menisci without significant osteoarthritic changes secreted more IL-7 than healthy young menisci while older osteoarthritic menisci secreted more IL-7 and granulocyte-macrophage colony-stimulating factor than healthy older menisci. CONCLUSIONS: Aged vervets develop naturally occurring knee osteoarthritis that includes involvement of the meniscus. Degenerative menisci secreted markedly increased amounts of matrix-degrading enzymes and inflammatory cytokines. These factors would be expected to act on the meniscus tissue and local joint tissues and may ultimately promote osteoarthritis development. These finding also suggest vervet monkeys are a useful animal model for studying the progression of osteoarthritis.

A reproducible radiation delivery method for unanesthetized rodents during periods of hind limb unloading.

Exposure to the spaceflight environment has long been known to be a health challenge concerning many body systems. Both microgravity and/or ionizing radiation can cause acute and chronic effects in multiple body systems. The hind limb unloaded (HLU) rodent model is a ground-based analogue for microgravity that can be used to simulate and study the combined biologic effects of reduced loading with spaceflight radiation exposure. However, studies delivering radiation to rodents during periods of HLU are rare. Herein we report the development of an irradiation protocol using a clinical linear accelerator that can be used with hind limb unloaded, unanesthetized rodents that is capable of being performed at most academic medical centers. A 30.5 cm×30.5 cm×40.6 cm30.5 cm×30.5 cm×40.6 cm rectangular chamber was constructed out of polymethyl methacrylate (PMMA) sheets (0.64 cm thickness). Five centimeters of water-equivalent material were placed outside of two PMMA inserts on either side of the rodent that permitted the desired radiation dose buildup (electronic equilibrium) and helped to achieve a flatter dose profile. Perforated aluminum strips permitted the suspension dowel to be placed at varying heights depending on the rodent size. Radiation was delivered using a medical linear accelerator at an accelerating potential of 10 MV. A calibrated PTW Farmer ionization chamber, wrapped in appropriately thick tissue-equivalent bolus material to simulate the volume of the rodent, was used to verify a uniform dose distribution at various regions of the chamber. The dosimetry measurements confirmed variances typically within 3%, with maximum variance <10% indicated through optically stimulated luminescent dosimeter (OSLD) measurements, thus delivering reliable spaceflight-relevant total body doses and ensuring a uniform dose regardless of its location within the chamber. Due to the relative abundance of LINACs at academic medical centers and the reliability of their dosimetry properties, this method may find great utility in the implementation of future ground-based studies that examine the combined spaceflight challenges of reduced loading and radiation while using the HLU rodent model.

Unplanned Transfers from Hospital Wards to the Neurological Intensive Care Unit.

BACKGROUND: The aim of this study is to evaluate the characteristics of unplanned transfers of adult patients from hospital wards to a neurological intensive care unit (NICU). METHODS: We retrospectively reviewed consecutive unplanned transfers from hospital wards to the NICU at our institution over a 3-year period. In-hospital mortality rates were compared between patients readmitted to the NICU ("bounce-back transfers") and patients admitted to hospital wards from sources other than the NICU who were then transferred to the NICU ("incident transfers"). We also measured clinical characteristics of transfers, including source of admission and indication for transfer. RESULTS: A total of 446 unplanned transfers from hospital wards to the NICU occurred, of which 39% were bounce-back transfers. The in-hospital mortality rate associated with all unplanned transfers to the NICU was 17% and did not differ significantly between bounce-back transfers and incident transfers. Transfers to the NICU within 24 h of admission to a floor service accounted for 32% of all transfers and were significantly more common for incident transfers than bounce-back transfers (39 vs. 21%, p = .0002). Of patients admitted via the emergency department who had subsequent incident transfers to the NICU, 50% were transferred within 24 h of admission. CONCLUSIONS: Unplanned transfers to an NICU were common and were associated with a high in-hospital mortality rate. Quality improvement projects should target the triage process and transitions of care to the hospital wards in order to decrease unplanned transfers of high-risk patients to the NICU.

Outcomes of intravenous tissue plasminogen activator for acute ischaemic stroke in HIV-infected adults.

BACKGROUND AND PURPOSE: To our knowledge there are no studies reporting the use and short-term outcomes of intravenous tissue plasminogen activator (IV-TPA) for the treatment of acute ischaemic stroke (AIS) in people living with HIV. METHODS: The US Nationwide Inpatient Sample (NIS) (2006-2010) was searched for HIV-infected AIS patients treated with IV-TPA. RESULTS: In the NIS, 2.2% (62/2877) of HIV-infected AIS cases were thrombolyzed with IV-TPA (median age 52 years, range 27-78, 32% female, 22% Caucasian) vs. 2.1% (19 335/937 896) of HIV-uninfected cases (median age 72 years, range 17-102 years, 50% female, 74% Caucasian; P = 0.77). There were more deaths in HIV-infected versus uninfected patients with stroke (220/2877, 7.6% vs. 49 089/937 547, 5.2%, P < 0.001) but no difference in the proportion of deaths amongst IV-TPA-treated patients. The age- and sex-adjusted odds ratio for death following IV-TPA administration in HIV-infected versus uninfected patients was 2.26 (95% CI 1.12, 4.58), but the interaction on mortality between HIV and IV-TPA use was not statistically significant, indicating no difference in risk of in-hospital death by HIV serostatus with IV-TPA use. A higher number of HIV-infected patients remained in hospital versus died or were discharged at both 10 and 30 days (P < 0.01 at 10 and 30 days). No difference in the proportion of intracerebral hemorrhage in the two groups was found (P = 0.362). CONCLUSIONS: The in-hospital mortality is higher amongst HIV-infected AIS patients than HIV-uninfected patients. However, the risk of death amongst HIV-infected patients treated with IV-TPA is similar to HIV-uninfected groups.

Long-term treatment efficacy in primary inflammatory breast cancer by hormonal receptor- and HER2-defined subtypes.

BACKGROUND: Subtypes defined by hormonal receptor (HR) and HER2 status have not been well studied in inflammatory breast cancer (IBC). We characterized clinical parameters and long-term outcomes, and compared pathological complete response (pCR) rates by HR/HER2 subtype in a large IBC patient population. We also compared disease-free survival (DFS) and overall survival (OS) between IBC patients who received targeted therapies (anti-hormonal, anti-HER2) and those who did not. PATIENTS AND METHODS: We retrospectively reviewed the records of patients diagnosed with IBC and treated at MD Anderson Cancer Center from January 1989 to January 2011. Of those, 527 patients had received neoadjuvant chemotherapy and had available information on estrogen receptor (ER), progesterone receptor (PR), and HER2 status. HR status was considered positive if either ER or PR status was positive. Using the Kaplan-Meier method, we estimated median DFS and OS durations from the time of definitive surgery. Using the Cox proportional hazards regression model, we determined the effect of prognostic factors on DFS and OS. Results were compared by subtype. RESULTS: The overall pCR rate in stage III IBC was 15.2%, with the HR-positive/HER2-negative subtype showing the lowest rate (7.5%) and the HR-negative/HER2-positive subtype, the highest (30.6%). The HR-negative, HER2-negative subtype (triple-negative breast cancer, TNBC) had the worst survival rate. HR-positive disease, irrespective of HER2 status, had poor prognosis that did not differ from that of the HR-negative/HER2-positive subtype with regard to OS or DFS. Achieving pCR, no evidence of vascular invasion, non-TNBC, adjuvant hormonal therapy, and radiotherapy were associated with longer DFS and OS. CONCLUSIONS: Hormone receptor and HER2 molecular subtypes had limited predictive and prognostic power in our IBC population. All molecular subtypes of IBC had a poor prognosis. HR-positive status did not necessarily confer a good prognosis. For all IBC subtypes, novel, specific treatment strategies are needed in the neoadjuvant and adjuvant settings.

Determination of ambient ethanol concentrations in aqueous environmental matrixes by two independent analyses.

A new method for the determination of ethanol in aqueous environmental matrixes at nanomolar concentrations is presented and compared to an existing method that has been optimized for low-level alcohol determinations. The new analysis is based upon oxidation of ethanol by the enzyme alcohol oxidase obtained from the yeast Hansenula sp. which quantitatively produces acetaldehyde after reaction for 120 min at 40 °C and pH 9.0. The acetaldehyde reacts with 2,4-dinitrophenylhydrazine forming a hydrazone that is separated from interfering substances and quantified by high-performance liquid chromatography (HPLC) with UV detection at 370 nm. Comparison of initial acetaldehyde concentration with that after enzymatic oxidation yields the ethanol concentration with a corresponding detection limit of 10 nM. Analytical results were verified by intercomparison with a completely independent technique utilizing a solid-phase microextraction (SPME) Carboxen/PDMS SPME fiber. A 12 mL aqueous phase sample was heated at 50 °C for 10 min prior to loading onto the SPME fiber. Extraction of ethanol was performed by introducing the fiber into the headspace above a pH 4.4 buffered sample containing 30% NaCl for 20 min. Samples were agitated during heating and extraction by magnetic stirring at a rate of 750 rpm. The fiber was thermally desorbed for 1 min at 230 °C in the injection port of a gas chromatograph equipped with a flame ionization detector (FID) set at 250 °C. The resulting ethanol detection limit is 19 nM. Results of an intercomparison study between the enzymatic and SPME analyses produced a trend line with a slope of unity demonstrating that methods produced statistically equivalent ethanol concentrations in several natural waters including rainwater, fresh surface waters, and sediment pore waters.

Lower prevalence of silent brain infarcts in the physically active: the Northern Manhattan Study.

OBJECTIVE: To examine the independent association between physical activity and subclinical cerebrovascular disease as measured by silent brain infarcts (SBI) and white matter hyperintensity volume (WMHV). METHODS: The Northern Manhattan Study (NOMAS) is a population-based prospective cohort examining risk factors for incident vascular disease, and a subsample underwent brain MRI. Our primary outcomes were SBI and WMHV. Baseline measures of leisure-time physical activity were collected in person. Physical activity was categorized by quartiles of the metabolic equivalent (MET) score. We used logistic regression models to examine the associations between physical activity and SBI, and linear regression to examine the association with WMHV. RESULTS: There were 1,238 clinically stroke-free participants (mean age 70 ± 9 years) of whom 60% were women, 65% were Hispanic, and 43% reported no physical activity. A total of 197 (16%) participants had SBI. In fully adjusted models, compared to those who did not engage in physical activity, those in the upper quartile of MET scores were almost half as likely to have SBI (adjusted odds ratio 0.6, 95% confidence interval 0.4-0.9). Physical activity was not associated with WMHV. CONCLUSIONS: Increased levels of physical activity were associated with a lower risk of SBI but not WMHV. Engaging in moderate to heavy physical activities may be an important component of prevention strategies aimed at reducing subclinical brain infarcts.

Physical activity and risk of ischemic stroke in the Northern Manhattan Study.

BACKGROUND: It is controversial whether physical activity is protective against first stroke among older persons. We sought to examine whether physical activity, as measured by intensity of exercise and energy expended, is protective against ischemic stroke. METHODS: The Northern Manhattan Study is a prospective cohort study in older, urban-dwelling, multiethnic, stroke-free individuals. Baseline measures of leisure-time physical activity were collected via in-person questionnaires. Cox proportional hazards models were constructed to examine whether energy expended and intensity of physical activity were associated with the risk of incident ischemic stroke. RESULTS: Physical inactivity was present in 40.5% of the cohort. Over a median follow-up of 9.1 years, there were 238 incident ischemic strokes. Moderate- to heavy-intensity physical activity was associated with a lower risk of ischemic stroke (adjusted hazard ratio [HR] 0.65, 95% confidence interval [0.44-0.98]). Engaging in any physical activity vs none (adjusted HR 1.16, 95% CI 0.88-1.51) and energy expended in kcal/wk (adjusted HR per 500-unit increase 1.01, 95% CI 0.99-1.03) were not associated with ischemic stroke risk. There was an interaction of sex with intensity of physical activity (p = 0.04), such that moderate to heavy activity was protective against ischemic stroke in men (adjusted HR 0.37, 95% CI 0.18-0.78), but not in women (adjusted HR 0.92, 95% CI 0.57-1.50). CONCLUSIONS: Moderate- to heavy-intensity physical activity, but not energy expended, is protective against risk of ischemic stroke independent of other stroke risk factors in men in our cohort. Engaging in moderate to heavy physical activities may be an important component of primary prevention strategies aimed at reducing stroke risk.

Bone architectural and structural properties after 56Fe26+ radiation-induced changes in body mass.

High-energy, high-charge (HZE) radiation, including iron ions ((56)Fe(26+)), is a component of the space environment. We recently observed a profound loss of trabecular bone in mice after whole-body HZE irradiation. The goal of this study was to examine morphology in bones that were excluded from a (56)Fe(26+) beam used to irradiate the body. Using 10-week-old male Sprague-Dawley rats and excluding the hind limbs and pelvis, we irradiated animals with 0, 1, 2 and 4 Gy (56)Fe(26+) ions and killed them humanely after 9 months. Animals grew throughout the experiment. Trabecular bone volume, connectivity and thickness within the proximal tibiae were significantly lower than control in a dose-dependent manner. Irradiated animals generally had less body mass than controls, which largely accounted for the variability in bone parameters as determined by ANCOVA. Likewise, lower cortical parameters were associated with reduced mass. However, lesser trabecular thickness in the 4-Gy group could not be attributed to body mass alone. Indicators of bone metabolism were generally unchanged, suggesting stabilized turnover. Exposure to (56)Fe(26+) ions can alter trabecular microarchitecture in shielded bones. Reduced body mass seems to be correlated with these deficits of trabecular and cortical bone.

CEBPG regulates ERCC5/XPG expression in human bronchial epithelial cells and this regulation is modified by E2F1/YY1 interactions.

Marked inter-individual variation in lung cancer risk cannot be accounted for solely by cigarette smoke and other environmental exposures. Evidence suggests that variation in bronchial epithelial cell expression of key DNA repair genes plays a role. Variation in these genes correlates with variation in expression of CEBPG and E2F1 transcription factors. Here, we investigated the mechanistic basis for correlation of the DNA repair gene ERCC5 (previously known as XPG) with CEBPG and E2F1. CEBPG expression vector transfected into H23 or H460 cell lines up-regulated endogenous ERCC5 and also luciferase from a reporter construct containing 589 bp of ERCC5 5' regulatory region. A recognition site for CEBPG and a region containing sites for YY1 on the sense strand and E2F1 on the anti-sense strand participated in CEBPG up-regulation of ERCC5. CEBPG, E2F1 and YY1 binding to their respective sites were confirmed by electrophoretic mobility shift assay. Thus, we conclude that CEBPG regulates ERCC5 expression and this regulation is modified by E2F1/YY1 interactions. Several polymorphisms have been identified in these regions and, based on the data presented here, it is reasonable to hypothesize that they may contribute to risk for bronchogenic carcinoma.

A murine model for bone loss from therapeutic and space-relevant sources of radiation.

Cancer patients receiving radiation therapy are exposed to photon (gamma/X-ray), electron, and less commonly proton radiation. Similarly, astronauts on exploratory missions will be exposed to extended periods of lower-dose radiation from multiple sources and of multiple types, including heavy ions. Therapeutic doses of radiation have been shown to have deleterious consequences on bone health, occasionally causing osteoradionecrosis and spontaneous fractures. However, no animal model exists to study the cause of radiation-induced osteoporosis. Additionally, the effect of lower doses of ionizing radiation, including heavy ions, on general bone quality has not been investigated. This study presents data developing a murine model for radiation-induced bone loss. Female C57BL/6 mice were exposed to gamma, proton, carbon, or iron radiation at 2-Gray doses, representing both a clinical treatment fraction and spaceflight exposure for an exploratory mission. Mice were euthanized 110 days after irradiation. The proximal tibiae and femur diaphyses were analyzed using microcomputed tomography. Results demonstrate profound changes in trabecular architecture. Significant losses in trabecular bone volume fraction were observed for all radiation species: gamma, (-29%), proton (-35%), carbon (-39%), and iron (-34%). Trabecular connectivity density, thickness, spacing, and number were also affected. These data have clear implications for clinical radiotherapy in that bone loss in an animal model has been demonstrated at low doses. Additionally, these data suggest that space radiation has the potential to exacerbate the bone loss caused by microgravity, although lower doses and dose rates need to be studied.

Elucidating determinants of the plateau in oxygen consumption at VO2max.

BACKGROUND: A plateau in oxygen consumption (VO2) is the primary means of confirming that maximal oxygen uptake (VO2max) is attained during incremental exercise to fatigue. However, it is still unresolved what causes expression of a plateau in VO2 at the end of incremental exercise. OBJECTIVES: To elucidate incidence and identify determinants of the VO2 plateau in subjects of varying fitness. METHODS: Thirty subjects (mean (SD) age and VO2max 26.9 (9.8) years and 3.4 (0.8) litre/min respectively) were separated into three groups: endurance trained (ET; n = 9), recreationally active (Rec; n = 11), and strength/sprint trained (STR; n = 10). During three separate visits, subjects completed incremental treadmill exercise during which breath by breath gas exchange data were obtained. Body composition was measured using a three site skinfolds model. Force production of the knee extensors and flexors was assessed using isokinetic dynamometry. RESULTS: VO2max was significantly higher (p < 0.05) in the ET group vs STR and Rec. The change in VO2 (DeltaVO2) at VO2max was not different (p > 0.05) in the ET group (33.0 (27.3) ml/min) compared with the Rec group (30.3 (24.1) ml/min) and the STR group (44.4 (23.8) ml/min). No correlations (p > 0.05) were evident between DeltaVO2 at VO2max and VO2max (r = 0.05), fat-free mass (r = 0.12), and muscular strength (r = -0.12). CONCLUSIONS: The incidence of a plateau in VO2 at VO2max (from correlation data) is not due to factors related to training status or physical fitness of subjects, but is altered by analysis and interpretation of gas exchange data.

Oxidation of Fe(II) in rainwater.

Photochemically produced Fe(II) is oxidized within hours under environmentally realistic conditions in rainwater. The diurnal variation between photochemical production and reoxidation of Fe(II) observed in our laboratory accurately mimics the behavior of ferrous iron observed in field studies where the highest concentrations of dissolved Fe(ll) occur in afternoon rain during the period of maximum sunlight intensity followed by gradually decreasing concentrations eventually returning to early morning pre-light values. The experimental work presented here, along with the results of kinetics studies done by others, suggests thatthe primary process responsible for the decline in photochemically produced Fe(II) concentrations is oxidation by hydrogen peroxide. This reaction is first order with respect to both the concentrations of Fe(II) and H2O2. The second-order rate constant determined for six different authentic rain samples varied over an order of magnitude and was always less than or equal to the rate constant determined for this reaction in simple acidic solutions. Oxidation of photochemically produced ferrous iron by other oxidants including molecular oxygen, ozone, hydroxyl radical, hydroperoxyl/superoxide radical, and hexavalent chromium were found to be insignificant under the conditions present in rainwater. This study shows that Fe(II) occurs as at least two different chemical species in rain; photochemically produced Fe(II) that is oxidized over time periods of hours, and a background Fe(II) that is protected against oxidation, perhaps by organic complexation, and is stable against oxidation for days. Because the rate of oxidation of photochemically produced Fe(II) does not increase with increasing rainwater pH, the speciation of this more labile form of Fe(II) is also not controlled by simple hydrolysis reactions.

Organic complexation of Fe(II) and its impact on the redox cycling of iron in rain.

More than 80% of the iron(II) present in a dilute (pH 4.5) H2SO4 solution was oxidized by hydrogen peroxide (3 microM) in 24 h, whereas in rainwater Fe(II) remained stable for days indicating that a complexed form of Fe(II) exists in rainwater that protects it against oxidation. When a rain sample was irradiated for 2 h with simulated sunlight, there was a 57 nM increase in Fe(II) resulting from photoreduction of organic Fe(III) complexes. Once irradiation ceased, the photoproduced Fe(II) rapidly oxidized back to its initial concentration of 32 nM prior to irradiation, but not to zero. These photochemical studies demonstrate that during the daytime when sunlight is present there are dynamic interconversions between complexed and uncomplexed Fe(II) and Fe(III) species in rainwater. During the night, after the photochemically produced Fe(II) is reoxidized to Fe(III), virtually all remaining Fe(II) is complexed by ligands which resist further oxidation. Rain samples oxidized under intense UV light lost their ability to stabilize Fe(II), suggesting the ligands stabilizing Fe(II) are organic compounds destroyed by UV-irradiation. Additional UV-irradiation studies demonstrated that on average 25% of the Fe-complexing ligands in rainwater are extremely strong and cannot be detected by spectrophotometric analysis using ferrozine. The stability of organically complexed Fe(II) has important implications for the bioavailability of rainwater-derived Fe in the surface ocean.

Photochemical production of Fe(II) in rainwater.

Significant concentrations of Fe(II) were produced upon irradiation of authentic rainwater with simulated sunlight. The magnitude of photoproduction was dependent on initial Fe(II), Fe(III), and hydrogen ion concentrations, with more Fe(II) photoproduction when initial Fe(III) and H+ concentrations were high and initial Fe(II) concentrations were low. An equation was developed that accurately predicts photoproduction of Fe(II) in rainwater based on initial Fe speciation values and pH. The quantum yield of Fe(II) photochemical production in rain decreased dramatically with increasing wavelength and decreasing energy of incoming radiation with the average quantum yield at 265 nm approximately an order of magnitude greater than at 546 nm. Probable photochemical precursors of Fe(II) in authentic rain include iron(III) oxalate, iron(III) hydroxide, and an undefined Fe(III) complex. The wavelength-dependent Fe(II) production was modeled using the average Fe(II) efficiency spectrum, an average rainwater absorption spectrum, and the modeled actinic flux for temperate latitudes in both summer and winter. The response spectrum has the highest photoproduction of Fe(II) in summer and winter at 325 and 330 nm, respectively, with greater production in summer rain due to increased actinic flux and longer hours of irradiation.

Visuospatial attention: the role of target contrast and task difficulty when assessing the effects of cues.

Cueing paradigms have become popular in assessing the processes of attention. In two experiments we manipulated (i) the contrast of the target, and (ii) the similarity between the targets discriminated. We used a cue that would isolate the exogenous component of attention. Both a reduction in target contrast and an increase in target similarity raised overall reaction times by a similar amount; however, the target contrast manipulation produced a much greater cueing effect compared with the target similarity manipulation. The results suggest that manipulation of target contrast changes the attention cueing effect at a stage of attracting attention to a location of the target (the 'move' stage), rather than at a later processing stage.