Nutrient tracers

Lazof DB, Goldsmith JKG, Rufty TW, Suggs C, Linton RW. The preparation of cryosections from plant tissue an alternative method appropriate for secondary ion mass spectrometry studies of nutrient tracers and trace metals. JMicrosc 1994 176 99-109. 

Some aspects of the biochemistry of metabolic processes affecting nutrients appear to have significant consequences for the expected behavior of stable carbon isotopes as tracers of diet. Specifically, we have seen that the simple model of a total scrambling of carbon atoms during endogenous biosynthesis is inconsistent with the expected pathways of some nutrients, whereas other isotopic records in ancient human tissues can be adequately accounted for by this model. 

D. Kirkham and W. V. Bartholomew, Equations for following nutrient transformation in soil, utilizing tracer data. Soil. Sci. Soc. Am. Proc. 1833 (1954). 

One issue which has not yet been addressed is the depth at which the southward flow of deep water occurred in the past. It is possible, for instance, that true NADW did weaken at the LGM, as is suggested by the nutrient-like tracers of water masses, but that this decrease was largely compensated by increases in flow higher in the water column. This issue could be investigated using ( Paxs/ Thxs) if cores from a variety of depths were analyzed. 

The permselectivity of the corneal and conjunctival paracellular routes was investigated by Huang et al. [159] in an attempt to show that nutrients can be extracted from the blood by the conjunctiva. Neither the blood vessels supplying the conjunctiva nor its basement membrane are rate-limiting to the transport of horseradish peroxidase. This 40 kDa tracer is restricted underneath the conjuncti-... 

Quantitative measurement of diffusional uptake and carrier-mediated transport of nutrients and drugs in experimental animals was greatly facilitated with the introduction of Olden dorfs brain uptake index (BUI) [42].Test and reference tracers are injected as an intraarterial bolus into the carotid artery of the anaesthetized animal. After 5 s the animal is killed and the brain is removed for radioactivity counting. This method measures the ratio of the unidirectional brain extraction, E, of the test substance and of the reference ([ H]-water, [ " C]-butanol), which are labelled with different isotopes, during a single passage through the brain capillary bed ... 

Iodine is an essential nutrient element required for thyroid gland. It is added to salt and to animal feeds for the prevention of goiter. In medicine it is used as a therapeutic reagent for the treatment of various thyroid-related diseases. It also is used as an antiseptic. Radioactive isotopes of iodine are used for treating thyroid cancer, heart diseases including tachycardia, and as a tracer for diagnosing certain diseases. 

The process of reductive dechlorination requires the presence of a readily oxidizable substrate or electron donor. The addition of nitrogen and phosphorous nutrients may be required. Because oxygen is detrimental to an anaerobic process, oxygen scavengers may be required to drive the process. Tracers to monitor the biological process may also be necessary. 

Isotopes of oxygen and hydrogen are useful tracers of water sources because they are constituents of the water molecule itself and because they are conservative in aquifers at near-surface temperatures. Isotopic techniques take advantage of the fact that lakes and their surrounding ground-water systems are usually isotopically distinct. Applications of stable isotopes for the study of lakes were first described by Dincer (10) and were discussed in several subsequent review articles (11-14). Most applications of isotopic techniques to lake systems are designed for the determination of water balances, nutrient-uptake studies, and paleotemperature reconstructions. 

Figure 3. Experimental design. Diagram showing additions of nutrients and tracer amounts of 15N into the divided arctic lake, N2.

Encapsulated within the pores of soils are aqueous solutions, the so-called soil solutions. Radio-tracer experiments have shown that there is a rapid, dynamic equilibrium between metal ions in the soil phase and the soil solutions. Hence, the soil solution is regarded as the transport medium for moving the essential nutrients from soils to plants. The soil solutions are highly variable in composition and properties, e.g. the pH can vary over the range 2-11. Alkaline soils are notorious for causing metal ion deficiency in plants, principally because many of the micronutrients form insoluble hydroxides and so are biologically unavailable. 

From the above it can be concluded that in many instances the introduction of an artificial radionuclide into the environment provides us with a natural tracer experiment. Indeed, this is the basis for the application of deterministic compartmental models, based on tracer kinetics, to radioecology (Whicker and Schultz, 1982). This approach is largely based on the assumption that radionuclide movements will exhibit first order kinetics although the existence of naturally-occurring tracees (stable isotopes) at relatively high abundance may result in more complex concentration-dependent kinetics. Furthermore, nutrient analogues may exert even more complex effects on processes such as radioion absorption across root plasma membranes this will become evident later in the chapter. 

Various modifications are reported with respect to the experimental setup (single pass or recirculated intestinal perfusion) as well as the site of blood collection, e.g. mesenteric vessels for estimation of the intestinal absorption rate (DeGraw RT, Anderson BD 2004). vs. peripheral veins for estimation of systemic availability of the candidate compound. This method is widely used for investigation of intestinal absorption of nutrients by using radioactive tracers (e.g. cholesterol, glucose) and their interference with the candidate compound (Arts et al. 2004). In addition the secretion of the candidate compound into the intestine can be studied by peripheral administration of the compound into a peripheral vein and subsequent determination of the appearance of the candidate compound in the intestinal perfusate (Merino et al. 2003 Berggren et al. 2004). Also variations are reported using chronically isolated intestinal loops in rats (Poelma et al. 1992). 

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