Factors controlling endogenous N-nitrosation

Table 4 summarizes the factors limiting endogenous N-nitrosation by bacteria and their likely relative importance. It is now well established that NNOCs are formed in large amounts in the hypochlorhydric stomach. Similar quantities would be expected in the urinary bladder when there is a complex flora. Large amounts would also be expected in the vagina of women with vaginitis, but only small amounts would be expected in saliva, in patients with small bowel overgrowth or in simple bladder infections.

Fat, fish, fish oil and cancer

There is an ecological association between total and animal fat consumption and colorectal and breast cancer risk. Mortality data for breast and colorectal cancer for 24 European countries correlated, as expected, with the consumption of animal, but not vegetable, fat. There was an inverse correlation with fish and fish oil consumption, when expressed as a proportion of total or animal fat, and this correlation was significant for both male and female colorectal cancer and for female breast cancer, whether the intakes were in the current time period, or 10 years or 23 years before cancer mortality. These effects were only seen in countries with a high ( > 85 g caput-1 day-1) animal fat intake. This evidence suggests that fish oil consumption is associated with protection against the promotional effects of animal fat in colorectal and breast carcinogenesis.

Dietary salt, nitrate and stomach cancer mortality in 24 countries. European Cancer Prevention (ECP) and the INTERSALT Cooperative Research Group

BACKGROUND

High salt and nitrate intake are considered as risk factors for stomach cancer, but little is known about possible interactions. This ecological study examines the respective importance of both factors for stomach cancer mortality at the population level using data obtained under standardized conditions and with biochemical analyses performed in the same laboratories.

METHODS

Randomly selected 24-hour urine samples from 39 populations, sampled from 24 countries (N = 5756 people for sodium, 3303 for nitrate) were obtained from the INTERSALT study. Median sodium and nitrate levels were age- and sex-standardized between ages 20-49 years and averaged per country. Ecological correlation-regression analyses were done in relation to national stomach cancer mortality rates.

RESULTS

The Pearson correlation of stomach cancer mortality with sodium for the 24 countries was: 0.70 in men and 0.74 in women (both P < 0.001) and with nitrate: 0.63 (P = 0.001) in men and (P < 0.005) in women. In multiple regression of stomach cancer mortality, using sodium and nitrate as independent variables the adjusted R2 was 0.61 in men and 0.54 in women (both P < 0.001). Addition of the interaction term (sodium x nitrate) to the previous model increased the adjusted R2 to 0.77 in men, and to 0.63 in women. The analysis of this model showed that the importance of nitrate as risk factor for stomach cancer mortality increased markedly with higher sodium levels. However, the relationship of stomach cancer mortality with sodium was always stronger than with nitrate.

CONCLUSIONS

Salt intake, measured as 24-hour urine sodium excretion, is likely the rate-limiting factor of stomach cancer mortality at the population level.

Twenty-four hour urinary nitrate excretion in 48 populations from 30 countries: an ECP-INTERSALT collaborative study

BACKGROUND

There is considerable interest in the possible role of nitrate in gastric carcinogenesis, but little information on nitrate intake around the world. This is the first study to give comprehensive standardised data on nitrate excretion as a marker of intake, using 48 worldwide population samples.

METHODS

Urinary nitrate excretion has been shown to be a valid measure of nitrate intake in people under 50. This report presents data on 24-hour urinary nitrate excretion from urine collections obtained in the INTERSALT study, based on random samples of men and women aged 20-49 from each of 48 population samples in 30 countries.

RESULTS

There was large variation in urinary nitrate excretion both within and between samples; within-sample (individual) distributions tended to be skewed towards higher values. Median values of the samples ranged from 0.42 mmol/day (Labrador, Canada) to 3.52 (Beijing, People's Republic of China) in men and 0.44 mmol/day (Colombia) to 3.44 (Beijing) in women. Overall, median values were higher in men than women by 11% on average (higher in men in 37 of 48 population samples). Comparison by geographical region of median values for men and women combined showed relatively low values in the samples in North America and Northern Europe (range 0.46-0.88 mmol/day), slightly higher values in Western Europe and Africa (0.68-1.11), and intermediate to high values in Southern Europe, Eastern and Central Europe and India (0.86-2.47). The highest median values were found in the Far Eastern samples (up to 3.48). Median values in the Central and South American samples ranged from 0.48 mmol/day (Colombia) to 1.37 (Xingu Indians of Brazil, and Argentina).

CONCLUSIONS

For the first time, these data give standardized information on urinary nitrate excretion from different geographical regions of the world, and provide a basis for the further exploration of the role of nitrate in the aetiology of disease in human populations.

Regional lung volume trajectories during expiratory flow in dogs

Parenchymal markers were placed in the left caudal lobes of anesthetized dogs, and the three-dimensional positions of the markers were tracked by biplane videofluoroscopy during expiration from total lung capacity (TLC) to approximately 30% TLC at steady expiratory flows of 0.3-7% TLC/s. Regional volumes of samples of parenchyma with volumes at TLC of 1-5 cm3 were obtained by computing the volumes of tetrahedral defined by taking the markers, four at a time, as apices of the tetrahedra, Regional volume (Vr), as a fraction of volume at TLC, was plotted against average volume (VL), as a fraction of volume at TLC, and Vr was fit by a quadratic function of VL. The initial slopes of the plots, dVr/dVL at VL = 1, varied by +/- 26% from the mean slope of 1. The curvatures were highly correlated with the slopes, and the Vr vs. VL plots formed a nest of "onion skins". The initial slopes were weakly correlated with the vertical position of the centroid of the tetrahedron, with the slope increasing by approximately 20%/cm, on average, in the dorsal direction in the supine dog. The vertical gradient in Vr accounted for approximately 30% of the total variability; small-scale heterogeneity contributed the remaining 70%. These results confirm earlier quasistatic measurements of nonuniform Vr and provide the first data on curvature of Vr trajectories. The mechanisms that cause the nongravitational component of Vr variability and the curvatures of the trajectories are unknown.

Nonuniform expansion of constricted dog lungs

The parenchymal marker technique was used to measure regional tidal volumes of samples of lung parenchyma in four open-chest supine dogs. Radiopaque markers that had been implanted in the lower lobe were tracked by biplane video fluoroscopy during sinusoidal volume oscillations at tidal volumes of approximately 20% of total lung capacity and frequencies of 1-40 breaths/min before and after methacholine was administered by aerosol. The volumes of tetrahedrons with apexes at four markers were computed, and sine waves were fit to the data for volume vs. time for each tetrahedron. The ratio of mean regional volume to mean airway pressure decreased by 10-45% after exposure to methacholine. Dynamic lung elastance and resistance of the constricted lungs were larger than control, and both were frequency dependent. Regional elastance and resistance varied considerably among tetrahedrons, and these were also frequency dependent. The data were fit by a model in which tissue elastance was uniform and nearly equal to elastance in the control state, but small-airway resistance was high and variable. We conclude that the lung contracts under bronchoconstriction but that the increased dynamic elastance and resistance of the constricted lung may be primarily the result of nonuniform increased airway resistance at the level of the terminal bronchioles.

Integration of satellite remote sensing, simple bioclimatic models and GIS for assessment of pastoral development for a commercial grazing enterprise

Satellite imagery, climatic, edaphic and topographic data, and a simple bioclimatic model were used to analyse the pastoral potential of a large cattle grazing enterprise, 'Cooplacurripa', on the central coast of New South Wales. Landsat Thematic Mapper and Spot XS satellite images were processed to create pasture growth status maps describing timbered and cleared areas, and priority areas for phosphorus fertiliser application. A digital elevation model was used to describe slope and aspect, and as a basis for interpolation of monthly surfaces of rainfall, temperature, radiation and evaporation from the Australian Climate Surfaces. These data were combined with a simple growth index model to create production surfaces for tropical, subtropical and temperature pasture types. The property was classified into zones defined by the seasonal growth patterns of the 3 pasture classes. The database was used to identify potential areas for further pasture improvement by a series of logical rules and map overlays to define pasture suitability for currently timbered areas with a slope of less than 20�. The northern section of the property with the highest rainfall, best suitability for temperate pasture and good road access was chosen for land capability and fauna impact studies on the basis of this analysis. The study provides an example of the application of spatial data to practical management issues in pastoral agriculture.

Perennial legumes for the high rainfall zone of eastern Australia. 1. Evaluation in single rows and selection of Caucasian clover (Trifolium ambiguum M. Bieb.)

A range of perennial legume species, including Trifolium ambiguum, T medium, Astragalus cicer, Coronilla varia, Lotus corniculatus, L. pedunculatus, and Lespedeza cuneata, were evaluated in glasshouse and field trials in 1989-92 at Armidale, New South Wales. Hexaploid germplasm of T. ambiguum was subjected to selection for increased seedling vigour, early biomass production and profuse flowering in glasshouse screening and spaced plant field nurseries. On an acid, solodic soil, T. ambiguum and T. medium grew modestly, Lotus spp. grew vigorously initially, but died out within 3 years, A. cicer and C. varia failed to persist beyond 1 year, but isolated plants of Lespedeza cuneata thrived. On an acid, freedraining, red-basalt soil, all accessions grew vigorously until early 1991. During the succeeding drought, Lotus sp. died out, A. cicer thinned out on the acid soil, but T. ambiguum, T medium, and C. varia remained persistent and productive. A large nursery of A. cicer accessions on the same soil limed to 5 t/ha before planting remained vigorous to the present. Superior hexaploid material of T ambiguum selected from spaced plants, originated chiefly from CPI 43909 and the ARS-2678 germplasm collection from Utah, USA.

Potential adaptation zones for temperate pasture species as constrained by climate: a knowledge-based logical modelling approach

Potential adaptation zones were modelled for major temperate pasture species using climate data and knowledge-based logical rules. A GIs database was constructed using a 0.025 degree digital elevation model and the Australian Climate Surfaces to create layers of monthly mean climate data for Australia. Soil pH maps for New South Wales, Victoria, and south-eastern South Australia were digitised and added to the database. Simple models using logical operators were constructed using estimates of temperature and aridity thresholds for the main temperate pasture species. The logical models were executed using primary and derived climate layers to create raster maps of potential adaptation zones for pasture species in eastern and south-western Australia. Areas of adaptation on freehold/leasehold land were expressed relative to a potential temperate pasture adaptation zone described by the lower (arid) limit of annual legume adaptation in temperate Australia and the northern limit of lucerne adaptation. Potential adaptation within this area ranged from 66% for lucerne down to <20% for perennial ryegrass in eastern Australia, and 93% for subterranean clover down to zero for perennial ryegrass in south-western Australia. Utility of the species adaptation zones could be enhanced using soil pH maps: a zone for serradella in NSW was refined by restricting adaptation to areas of climatic suitability with low soil pH. Maps for lucerne and Mount Barker subterranean clover showed good agreement with validation data for NSW. The zones may be readily adjusted by simple changes to parameter values in the algorithms. This knowledge-based approach has potential as an aid to targeting resources for plant improvement or to provide advice for more efficient utilisation of existing commercial pasture plants.

Fish, n-3 fatty acids and human colorectal and breast cancer mortality

Although there is a strong positive association between total fat consumption and colorectal and breast cancer risk, there is evidence that n-3 fatty acids, mainly found in fish oil, are protective. If this is so, we would expect to be able to detect an inverse correlation between fish consumption and colorectal cancer and breast cancer mortality. Mortality data for breast and colorectal cancer in 24 European countries were correlated with current fish and fish oil consumption and with consumption 10 and 23 years previously. In males there was an inverse correlation between colorectal cancer mortality and current intake of fish (P = 0.036), a weaker correlation with fish consumption 10 years earlier (P = 0.042) and none with consumption 23 years earlier (P = 0.12). The data were not statistically significant in females. There was no correlation at all between breast cancer mortality and fish or fish oil consumption at any time. It is concluded that fish consumption is associated with protection against the later promotional stages of colorectal carcinogenesis, but not with the early initiation stages. The results are discussed in terms of the role of prostaglandins in colorectal carcinogenesis.

Diet and chemoprevention of colorectal cancer

There is copious evidence of the importance of diet in the causation of colorectal cancer. This comes from studies of populations, case-control studies, and prospective or cohort studies. The evidence from epidemiology is now beginning to treach a clear concensus that the disease is associated with high intakes of fat and meat and low intakes of cereal fibre, fruit and vegetables. There are various ways in which these observations are being applied to colorectal cancer prevention. These include dietary advice to populations and specific advice given to individuals at high risk of the disease.

The association between typhoid carriage, typhoid infection and subsequent cancer at a number of sites

It has been demonstrated that bacteria can produce the very potent carcinogens (N-nitroso compounds), from nitrite and suitable amines. It has been hypothesized that this can happen whenever a body site which is normally sterile becomes colonized by bacteria. If this is so then such chronic infections should result in an increased incidence of local cancers and also of cancers at some distant sites. To test this we studied the risk of cancer at various sites in a cohort of chronic carriers of Salmonella typhi/paratyphi. We have observed a greatly increased risk of cancers of the biliary tract and also of cancers of the colorectum, pancreas, lung and all sites. The results are discussed in terms of the hypothesis being tested.

Seedling vigour and rhizome development in Trifolium ambiguum M. Bieb. (Caucasian clover) as affected by density of companion grasses, fertility, drought and defoliation in the first year

Trifolium ambiguum was grown from seed in a mixture with Festuca arundinacea and Phalaris aquatica at four grass densities under high fertility, and at two intermediate grass densities under low fertility, with frequent or infrequent defoliation imposed from week 15 to week 31, in large pots for 1 year. Selective defoliation of the clover at week 35, and 3-4 weeks drought were imposed on high and low fertility treatments in the post-cutting period. The impact of these treatments was assessed by destructive harvest of shoots, roots and rhizomes. Plant densities of T. ambiguum and grasses were unaffected by the treatments; however, rhizome numbers were reduced by increasing density of grasses, by frequent defoliation, and at high fertility compared with low fertility where grass vigour was very poor. Selective defoliation of T. ambiguum and short-term drought temporarily reduced the contribution of T. ambiguum to harvested herbage, but had no permanent effect on growth rate. Final root and rhizome biomass of T. ambiguum was reduced by increasing density of grass, by frequent defoliation and at high fertility where grass competition was vigorous. We conclude that early growth of T. ambiguum, in particular root and rhizome development, may be better where the density of companion grasses is low, or grass vigour is low due to low fertility, provided soil P and S are not limiting for clover growth. Defoliation in the presence of vigorous grass competition reduces root and rhizome development and may not be effective in minimizing competition. Options for inclusion of T. ambiguum in mixed swards are discussed.

Cancer mortality in chronic typhoid and paratyphoid carriers

It has been shown in vitro that bacteria are able to form or release carcinogens, mutagens, or promoters from intestinal secretions such as bile, or from excretions such as urine. It is, therefore, of interest to find out whether chronic infection of the gallbladder is associated with carcinogens, as in chronic infection of the urinary bladder. A study of cancer risk in chronic typhoid and paratyphoid carriers showed a large excess (observed/expected cases) for cancer of the gallbladder (167.0; 95% confidence interval 54.1-389) and also excess risks of cancer of the pancreas (8.1), colorectum (3.0), lung (2.5), and all neoplasms (2.6). There was no similar excess risk in a group of 386 people with typhoid from the 1964 Aberdeen outbreak. This indicates that it is long-term typhoid carriage, not acute infection, which is the risk factor. This has important implications for cancer prevention. Eradication of chronic carriage, by use of antibiotics or elective cholecystectomy, should be re-emphasised, and the need for good documentation of carriers is, therefore, of great importance.