Stability of 3-bromotyrosine in serum and serum 3-bromotyrosine concentrations in dogs with gastrointestinal diseases

Abstract BACKGROUND: 3-Bromotyrosine (3-BrY) is a stable product of eosinophil peroxidase and may serve as a marker of eosinophil activation. A gas chromatography/mass spectrometry method to measure 3-BrY concentrations in serum from dogs has recently been established and analytically validated. The aims of this study were to determine the stability of 3-BrY in serum, to determine the association between peripheral eosinophil counts and the presence of an eosinophilic infiltrate in the gastrointestinal tract, and to compare serum 3-BrY concentrations in healthy dogs (n = 52) and dogs with eosinophilic gastroenteritis (EGE; n = 27), lymphocytic-plasmacytic enteritis (LPE; n = 25), exocrine pancreatic insufficiency (EPI; n = 26), or pancreatitis (n = 27). RESULTS: Serum 3-BrY concentrations were stable for up to 8, 30, and 180 days at 4°C, -20°C, and -80°C, respectively. There was no significant association between peripheral eosinophil count and the presence of eosinophils in the GI tissues (P = 0.1733). Serum 3-BrY concentrations were significantly higher in dogs with EGE (median [range] = 5.04 [≤0.63-26.26] μmol/L), LPE (median [range] = 3.60 [≤0.63-15.67] μmol/L), and pancreatitis (median [range] = 1.49 [≤0.63-4.46] μmol/L) than in healthy control dogs (median [range] = ≤0.63 [≤0.63-1.79] μmol/L; P < 0.0001), whereas concentrations in dogs with EPI (median [range] = 0.73 [≤0.63-4.59] μmol/L) were not different compared to healthy control dogs. CONCLUSIONS: The present study revealed that 3-BrY concentrations were stable in serum when refrigerated and frozen. No relationship between peripheral eosinophil count and the presence of eosinophils infiltration in the GI tissues was found in this study. In addition, serum 3-BrY concentrations were increased in dogs with EGE, but also in dogs with LPE and pancreatitis. Further studies are needed to determine whether measurement of 3-BrY concentrations in serum may be useful to assess patients with suspected or confirmed EGE or LPE.

Premature Discontinuation of Randomized Trials in Critical and Emergency Care: A Retrospective Cohort Study.

OBJECTIVES Randomized clinical trials that enroll patients in critical or emergency care (acute care) setting are challenging because of narrow time windows for recruitment and the inability of many patients to provide informed consent. To assess the extent that recruitment challenges lead to randomized clinical trial discontinuation, we compared the discontinuation of acute care and nonacute care randomized clinical trials. DESIGN Retrospective cohort of 894 randomized clinical trials approved by six institutional review boards in Switzerland, Germany, and Canada between 2000 and 2003. SETTING Randomized clinical trials involving patients in an acute or nonacute care setting. SUBJECTS AND INTERVENTIONS We recorded trial characteristics, self-reported trial discontinuation, and self-reported reasons for discontinuation from protocols, corresponding publications, institutional review board files, and a survey of investigators. MEASUREMENTS AND MAIN RESULTS Of 894 randomized clinical trials, 64 (7%) were acute care randomized clinical trials (29 critical care and 35 emergency care). Compared with the 830 nonacute care randomized clinical trials, acute care randomized clinical trials were more frequently discontinued (28 of 64, 44% vs 221 of 830, 27%; p = 0.004). Slow recruitment was the most frequent reason for discontinuation, both in acute care (13 of 64, 20%) and in nonacute care randomized clinical trials (7 of 64, 11%). Logistic regression analyses suggested the acute care setting as an independent risk factor for randomized clinical trial discontinuation specifically as a result of slow recruitment (odds ratio, 4.00; 95% CI, 1.72-9.31) after adjusting for other established risk factors, including nonindustry sponsorship and small sample size. CONCLUSIONS Acute care randomized clinical trials are more vulnerable to premature discontinuation than nonacute care randomized clinical trials and have an approximately four-fold higher risk of discontinuation due to slow recruitment. These results highlight the need for strategies to reliably prevent and resolve slow patient recruitment in randomized clinical trials conducted in the critical and emergency care setting.

Racing against Time: Varying Patterns of Social Mobilization in Serbia and Georgia

After the collapse of the Soviet Union and Yugoslavia, a number of actors started to engage in the power struggle for the opportunities to shape the new order in successive nation-states. In Serbia and Georgia historically hegemonic Orthodox Christian churches were among the firsts in the frontlines for political and economic power. More than a decade has passed since the so-called Coloured Revolutions in Georgia and Serbia, and the Orthodox churches still remain participants of an ongoing socio-political transition of these states. The revival of public role of religion appeared temporary in Serbia followed by a gradual decline of an influence of the Orthodox Church over political life and legal process. However, in Georgia the public and political role of religion increased rather than declined albeit changed shape. Examining the degree to which the two Orthodox churches can influence the political agenda in Serbia and Georgia, the paper attempts to understand how church-State relations work in practice. By bringing rich empirical data from the field (70 interviews with (arch)bishops, priests and religious clerics in Georgia and Serbia added to field observations), the paper reflects on the themes under which the two Orthodox churches mobilize public protest in Serbia and Georgia. The paper further looks at varying State responses and their broader implication for church-state problematique.

Influence of sample matrix on the alkaline extraction of Cr(VI) in soils and industrial materials

An accurate and efficient determination of the highly toxic Cr(VI) in solid materials is important to determine the total Cr(VI) inventory of contaminated sites and the Cr(VI) release potential from such sites into the environment. Most commonly, total Cr(VI) is extracted from solid materials following a hot alkaline extraction procedure (US EPA method 3060A) where a complete release of water-extractable and sparingly soluble Cr(VI) phase is achieved. This work presents an evaluation of matrix effects that may occur during the hot alkaline extraction and in the determination of the total Cr(VI) inventory of variably composed contaminated soils and industrial materials (cement, fly ash) and is compared to water-extractable Cr(VI) results. Method validation including multiple extractions and matrix spiking along with chemical and mineralogical characterization showed satisfying results for total Cr(VI) contents for most of the tested materials. However, unreliable results were obtained by applying method 3060A to anoxic soils due to the degradation of organic material and/or reactions with Fe2+-bearing mineral phases. In addition, in certain samples discrepant spike recoveries have to be also attributed to sample heterogeneity. Separation of possible extracted Cr(III) by applying cation-exchange cartridges prior to solution analysis further shows that under the hot alkaline extraction conditions only Cr(VI) is present in solution in measurable amounts, whereas Cr(III) gets precipitated as amorphous Cr(OH)3(am). It is concluded that prior to routine application of method 3060A to a new material type, spiking tests are recommended for the identification of matrix effects. In addition, the mass of extracted solid material should to be well adjusted to the heterogeneity of the Cr(VI) distribution in the material in question.

Predictors of weight stability in women and men: The aerobic center longitudinal study, 1987--1995

It is estimated that more than half the U.S. adult population is overweight or obese as classified by a body mass index of 25.0–29.9 or ≥30 kg/m 2, respectively. Since the current treatment approaches for long-term maintenance of weight loss are lacking, the National Institutes of Health state that an effective approach may be to focus on weight gain prevention. There is a limited body of literature describing how adults maintain a stable weight as they age. It is hypothesized that weight stability is the result of a balance between energy consumption and energy expenditure as influenced by diet, lifestyle, behavior, genetics and environment. The purpose of this research was to examine the dietary intake and behaviors, lifestyle habits, and risk factors for weight change that predict weight stability in a cohort of 2101 men and 389 women aged 20 to 8 7 years in the Aerobic Center Longitudinal Study regardless of body weight at baseline. At baseline, participants completed a maximal exercise treadmill test to determine cardiorespiratory fitness, a medical history questionnaire, which included self-reported measures of weight, dietary behaviors, lifestyle habits, and risk factors for weight change, a three-day diet record, and a mail-back version of the medical history questionnaire in 1990 or 1995. All analyses were performed separately for men and women. Results from multivariate regression analyses indicated that the strongest predictor of follow-up weight for men and women was previous weight, accounting for 87.0% and 81.9% of the variance, respectively. Age, length of follow-up and eating habits were also significant predictors of follow-up weight in men, though these variables only explained 3% of the variance. For women, length of follow-up and currently being on a diet were significantly associated with follow-up weight but these variables explained only an additional 2% of the variance. Understanding the factors that influence weight change has tremendous public health importance for developing effective methods to prevent weight gain. Since current weight was the strongest predictor of previous weight, preventing initial weight gain by maintaining a stable weight may be the most effective method to combat the increasing prevalence of overweight and obesity. ^

NFkappaB and STAT binding elements participate in regulation of MUC1 expression in normal and transformed mammary epithelial cells

The MUC1 gene encodes a transmembrane mucin glycoprotein that is overexpressed in several cancers of epithelial origin, including those of breast, pancreas, lung, ovary, and colon. Functions of MUC1 include protection of mucosal epithelium, modulation of cellular adhesion, and signal transduction. Aberrantly increased expression of MUC1 in cancer cells promotes tumor progression through adaptation of these functions. Some regulatory elements participating in MUC1 transcription have been described, but the mechanisms responsible for overexpression are largely unknown. A region of MUC1 5′ flanking sequence containing two conserved potential cytokine response elements, an NFκB site at −589/−580 and a STAT binding element (SBE) at −503/−495, has been implicated in high level expression in breast and pancreatic cancer cell lines. Persistent stimulation by proinflammatory cytokines may contribute to increased MUC1 transcription by tumor cells. ^ T47D breast cancer cells and normal human mammary epithelial cells (HMEC) were used to determine the roles of the κB site and SBE in basal and stimulated expression of MUC1. Treatment of T47D cells and HMEC with interferon-γ (IFNγ) alone enhanced MUC1 expression at the level of transcription, and the effect of IFNγ was further stimulated by tumor necrosis factor-α (TNFα). MUC1 responsiveness to these cytokines was modest in T47D cells but clearly evident in HMEC. Transient transfection of T47D cells with mutant MUC1 promoter constructs revealed that the κB site at −589/−580 and the SBE at −503/−495 and were required for cooperative stimulation by TNFα and IFNγ. Electrophoretic mobility shift assays (EMSA) revealed that the synergy was mediated not by cooperative binding of transcription factors but by the independent actions of STAT1α and NFκB p65 on their respective binding sites. Independent mutations in the κB site and SBE abrogated cytokine responsiveness and reduced basal MUC1 promoter activity by 45–50%. However, only the κB site appeared to be constitutively activated in T47D cells, in part by NFκB p65. These findings implicate two cytokine response elements in the 5 ′ flanking region of MUC1, specifically a κB site and a STAT binding element, in overexpression of MUC1 in breast cancer cells. ^

Anticancer activity of OSW-1: Induction of apoptotic pathway in leukemia and autophagic death in pancreatic cancer through a calcium mediated mechanism

OSW-1 is a natural compound found in the bulbs of Orninithogalum saudersiae, a member of the lily family. This compound exhibits potent antitumor activity in vitro with the IC50 values in the low nanomolar concentration range and demonstrating its ability to kill drug resistant cancer cells. In an effort to discover the unknown mechanism of action of this novel compound as a potential anticancer agent, the main objective of this research project was to test the cytotoxicity of OSW-1 against various cancer lines, and to elucidate the biochemical and molecular mechanism(s) responsible for the anticancer activity of OSW-1. My initial investigation revealed that OSW-1 is effective in killing various cancer cells including pancreatic cancer cells and primary leukemia cells resistant to standard chemotherapeutic agents, and that non-malignant cells were less sensitive to this compound. Further studies revealed that in leukemia cells, OSW-1 causes a significant increase in cytosolic calcium and activates rapid calcium-dependent apoptosis by the intrinsic pathway. Additionally, OSW-1 treatment leads to the degradation of the ER chaperone GRP78/BiP implicated in the survival of cancer cells. Meanwhile, it shows a reduced sensitivity in respiration-deficient sub-clones of leukemia cells which had higher basal levels of Ca2+. Mechanistically, it was further demonstrated that cytosolic Ca2+ elevations were observed together with Na+ decreases in the cytosol, suggesting OSW-1 caused the calcium overload through inhibition of the Na+/Ca 2+exchanger (NCX). Although similar calcium disturbances were observed in pancreatic cancer cells, mechanistic studies revealed that autophagy served as an initial pro-survival mechanism subsequent to OSW-1 treatment but extended autophagy caused inevitable cell death. Furthermore, combination of OSW-1 with autophagy inhibitors significantly enhances the cytotoxicity against pancreatic cancer cells. Taken together, this study revealed the novel mechanism of OSW-1 which is through inhibition of the Na+/Ca2+ exchanger and provides a basis for using this compound in combination with other agents for the treatment of pancreatic cancer which is resistant to available anticancer drugs. ^

Involvement of lipocalin 2 in leukemia and breast cancer

Human lipocalin 2 is described as the neutrophil gelatinase-associated lipocalin (NGAL). The lipocalin 2 gene encodes a small, secreted glycoprotein that possesses a variety of functions, of which the best characterized function is organic iron binding activity. Elevated NGAL expression has been observed in many human cancers including breast, colorectal, pancreatic and ovarian cancers. I focused on the characterization of NGAL function in chronic myelogenous leukemia (CML) and breast cancer. Using the leukemic xenograft mouse model, we demonstrated that over-expression of NGAL in K562 cells, a leukemic cell line, led to a higher apoptotic rate and an atrophy phenotype in the spleen of inoculated mice compared to K562 cells alone. These results indicate that NGAL plays a primary role in suppressing hematopoiesis by inducing apoptosis within normal hematopoietic cells. In the breast cancer project, we analyzed two microarray data sets of breast cancer cell lines ( n = 54) and primary breast cancer samples (n = 318), and demonstrated that high NGAL expression is significantly correlated with several tumor characteristics, including negative estrogen receptor (ER) status, positive HER2 status, high tumor grade, and lymph node metastasis. Ectopic NGAL expression in non-aggressive (ZR75.1 and MCF7) cells led to aggressive tumor phenotypes in vitro and in vivo. Conversely, knockdown of NGAL expression in various breast cancer cell lines by shRNA lentiviral infection significantly decreased migration, invasion, and metastasis activities of tumor cells both in vitro and in vivo . It has been previously reported that transgenic mice with a mutation in the region of trans-membrane domain (V664E) of HER2 develop mammary tumors that progress to lung metastasis. However, we observed that genetic deletion of the 24p3 gene, a mouse homolog of NGAL, in HER2 transgenic mice by breeding with 24p3-null mice resulted in a significant delay of mammary tumor formation and reduction of lung metastasis. Strikingly, we also found that treatment with affinity purified 24p3 antibodies in the 4T1 breast cancer mice strongly reduced lung metastasis. Our studies provide evidence that NGAL plays a critical role in breast cancer development and progression, and thus NGAL has potential as a new therapeutic target in breast cancer.^

A methodologic study of pain assessment in Anglo and Hispanic children with cancer

There is growing clinical evidence that even young children experience pain and accompanying anxiety. Few instruments have been validated to assess pain characteristics in children. The study of related demographic, illness, psychologic and parental factors in children has also been limited. This study examines the reliability and validity of pain assessment tools in an outpatient pediatric cancer population. A total of 78 children from three to fifteen years of age were observed and interviewed about the pain of invasive procedures. The effect of cultural factors and the stress of acculturation were examined by comparing data from two cultural groups, Anglo and Hispanic.^ Spielberger State-Trait Anxiety Scales were administered to children and parents prior to an invasive procedure. The Procedure Behavioral Checklist (PBCL) was used for observation of the child's response during the procedure. The Children's Procedural Interview (CPI) which contains items on the PBCL and visual analogues (scales of faces indicating varying degrees of pain and anxiety) was administered following the procedure.^ Reliability coefficients for Anglos were.78 on the PBCL,.79 on the CPI and.85 on the visual analogue scales. For Hispanics, the reliability for the PBCL was.54, while the CPI had a reliability of.72 and the visual analogue scales,.87. Construct validity was demonstrated by high correlations between the PBCL and CPI scores for both ethnic groups (.66 for Anglos and.64 for Hispanics) and by the significant correlation of State anxiety scores with both PBCL and CPI scores. Age was inversely correlated with PBCL and CPI scores for both ethnic groups. Hispanic parents' anxiety scores were higher than Anglo parents, but were not highly correlated with their child's PBCL, CPI or State-Trait anxiety scores. Caregivers' ratings were correlated with the PBCL scores for Anglos but not for Hispanics.^ The findings of this study indicate that pain responses may be reliably assessed using both observational and self-report methods in children, though differences in Anglo and Hispanic cultures exist. Differences in pain symptomatology and assessment in the two cultural groups warrant further study. ^

An examination of the cross-cultural reliability and construct validity of a measure of loneliness

Loneliness is a pervasive, rather common experience in American culture, particularly notable among adolescents. However, the phenomenon is not well documented in the cross-cultural psychiatric literature. For psychiatric epidemiology to encompass a wide array of psychopathologic phenomena, it is important to develop useful measures to characterize and classify both non-clinical and clinical dysfunction in diverse subgroups and cultures.^ The goal of this research was to examine the cross-cultural reliability and construct validity of a scale designed to measure loneliness. The Roberts Loneliness Scale (RLS-8) was administered to 4,060 adolescents ages 10-19 years enrolled in high schools along either side of the Texas-Tamaulipas border region between the U.S. and Mexico. Data collected in 1988 from a study focusing on substance use and psychological distress among adolescents in these regions were used to examine the operating characteristics of the RLS-8. A sample stratified by nationality and language, age, gender, and grade was used for analysis.^ Results indicated that in general the RLS-8 has moderate reliability in the U.S. sample, but not in the Mexican sample. Validity analyses demonstrated that there was evidence for convergent validity of the RLS-8 in the U.S. sample, but none in the Mexican sample. Discriminant validity of the measures in neither sample could be established. Based on the factor structure of the RLS-8, two subscales were created and analyzed for construct validity. Evidence for convergent validity was established for both subscales in both national samples. However, the discriminant validity of the measure remains unsubstantiated in both national samples. Also, the dimensionality of the scale is unresolved.^ One primary goal for future cross-cultural research would be to develop and test better defined culture-specific models of loneliness within the two cultures. From such scientific endeavor, measures of loneliness can be developed or reconstructed to classify the phenomenon in the same manner across cultures. Since estimates of prevalence and incidence are contingent upon reliable and valid screening or diagnostic measures, this objective would serve as an important foundation for future psychiatric epidemiologic inquiry into loneliness. ^

Growth regulatory role of R -PTPmu in normal and neoplastic epithelial cells

Cellular oncogenes and tumor suppressor genes regulate cellular adhesion and proliferation, two important events in malignant transformation. Even though receptor-like protein tyrosine phosphatases (R-PTPs) can influence these events, their role in malignant transformation has not been studied. The major goal of this study was to determine whether downregulation of R-PTP$\mu$ expression in lung epithelial cells is associated with or causal to neoplastic transformation. Examination of R-PTP$\mu$ expression in normal and carcinoma cells demonstrated that lung epithelial cells expressed R-PTP$\mu$ whereas lung carcinoma cells did not, and that incubation with TGF-$\alpha$ and HGF induced a two fold increase in R-PTP$\mu$ mRNA expression. To associate the expression of R-PTP$\mu$ with neoplastic transformation, we transfected lung epithelial cells with the H-ras oncogene. Transformation resulted in the activation of the MAPK signal transduction pathway, the hyperphosphorylation of c-met, and the production of HGF. Upon analysis of R-PTP$\mu$ expression, we observed a significant decrease in R-PTP$\mu$ mRNA and protein levels suggesting that transformation can directly or indirectly downregulate the expression of R-PTP$\mu.$ TGF-$\beta$ reversed the H-ras transformed phenotype, an event directly correlated with upregulation of R-PTP$\mu.$ To provide a casual relationship between R-PTP$\mu$ and cessation of tumor cell growth, we transfected carcinoma cells with the wild type R-PTP$\mu$ cDNA. Transiently expressing cells were selected by FACS using the mAb 3D7 and plated into individual wells. Carcinoma cells positive for R-PTP$\mu$ expression did not grow into colonies whereas non-R-PTP$\mu$ expressing carcinoma cells did, suggesting that expression of R-PTP$\mu$ arrested cell growth. To better understand the growth arrest induced by R-PTP$\mu$, we transfected the H-ras transformed lung epithelial cell line (MvLu-1-ras) with R-PTP$\mu$ (MvLu-1-ras/R-PTP$\mu$). Examination of growth factor receptor phosphorylation revealed significant inhibition of c-met and EGF-R. Furthermore, these cells underwent apoptosis in the absence of serum. Taken together the data demonstrate that the downregulation of R-PTP$\mu$ expression is an important step in neoplastic transformation of lung epithelial cells and that its presence can induce apoptosis and inhibit the signaling of c-met and EGF-R, two major growth factor receptors in lung carcinoma. In conclusion, the expression of R-PTP$\mu$ is inversely correlated with neoplastic transformation, growth and survival of tumor cells. ^

Stable carbon and oxygen isotope records of Cibicidoides wuellerstorfi in DSDP and ODP sites in the Atlantic and Pacific Ocean

Carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago, the interval when significant northern hemisphere glaciation began. The delta18O and delta13C data from four Atlantic sites (552, 607, 610, and 704) and one Pacific site (677) show that global cooling over this interval was associated with increased suppression of North Atlantic Deep Water (NADW) formation. However, the relative strength of NADW production was always greater than is observed during late Pleistocene glaciations when extreme decreases in NADW are observed in the deep North Atlantic. Our data indicate that an increase in the equator-to-pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the North Atlantic but rather the opposite occurred. This is not unexpected as it is the "warm high-salinity" characteristic, rather than the "low temperature", of thermocline waters that is critical to the deepwater formation process in this region today.

(Table 1.4) Ratios of petrogenic components in glassy and crystalline basalts from the north part of the Bougault anomaly, Mid-Atlantic Ridge 15°N

Structure and composition of sub-surface bottom sediments from the southwest Barents Sea have been under study. The study has revealed heterogeneity of sediment structure resulted from temporal irregularity and variability of sedimentation processes. The study of the heavy minerals from 0.1-0.01 mm grain size fraction has shown prevalence of green hornblende, epidote, garnet, and ilmenite in all types of sediments; these minerals are the basis of terrigenous-mineralogical province. At the same time in different areas local terrigenous-mineralogical associations have been identified. Clay mineral composition of in the sediments was quite uniform: biotite, chlorite, hydromica, smectite. Despite this, a number of features indicating initial stages of clay mineral transformation has been identified. Differences in material composition and structure of the studied sediments are associated with rapid change in paleogeographic situation on the land - ice cover melting on the Kola Peninsula and subsequent Holocene climatic situation.

Petrography and geochemistry of organic matter in Triassic and Cretaceous sediments from the Wombat and Exmouth Plateau

Triassic (Carnian-Rhaetian) continental margin sediments from the Wombat Plateau off northwest Australia (Sites 759, 760, 761, and 764) contain mainly detrital organic matter of terrestrial higher plant origin. Although deposited in a nearshore deltaic environment, little liptinitic material was preserved. The dominant vitrinites and inertinites are hydrogen-lean, and the small quantities of extractable bitumen contain w-alkanes and bacterial hopanoid hydrocarbons as the most dominant single gas-chromatography-amenable compounds. Lower Cretaceous sediments on the central Exmouth Plateau (Sites 762 and 763) farther south in general have an organic matter composition similar to that in the Wombat Plateau sediments with the exception of a smaller particle size of vitrinites and inertinites, indicating more distal transport and probably deposition in deeper water. Nevertheless, organic matter preservation is slightly better than in the Triassic sediments. Long-chain fatty acids, as well as aliphatic ketones and alcohols, are common constituents in the Lower Cretaceous sediments in addition to n-alkanes and hopanoid hydrocarbons. Thin, black shale layers at the Cenomanian/Turonian boundary, although present at several sites (Sites 762 and 763 on the Exmouth Plateau, Site 765 in the Argo Abyssal Plain, and Site 766 on the continental margin of the Gascoyne Abyssal Plain), are particularly enriched in organic matter only at Site 763 (up to 26%). These organic-matter-rich layers contain mainly bituminite of probable fecal-pellet origin. Considering the high organic carbon content, the moderate hydrogen indices of 350-450 milligrams of hydrocarbon-type material per gram of Corg, the maceral composition, and the low sedimentation rates in the middle Cretaceous, we suggest that these black shales were accumulated in an area of oxygen-depleted bottom-water mass (oceanwide reduced circulation?) underlying an oxygen-rich water column (in which most of the primary biomass other than fecal pellets is destroyed) and a zone of relatively high bioproductivity. Differences in organic matter accumulation at the Cenomanian/Turonian boundary at different sites off northwest Australia are ascribed to regional variations in primary bioproductivity.