Element turnover studies

Stable isotopes do not decay, which makes them a safe alternative to radiotracers, but also offers the possibility of following administered stable isotope labels in the human body over extended periods of time. This can be made use of in two different ways. Observational periods for compartmental analysis can be extended from a few days to months or even years, which allows better assessment of slowly 

Element losses together with element bioavailability determine how much of an element has to be provided through the diet to remain in element balance. For assessment of losses, a label needs to be administered once either orally or intravenously. Compartmental modeling techniques permit to calculate when the label has equilibrated with the natural element in all body compartments. When isotopic labeling has been achieved, continuous replacement of lost isotopic label with the natural element from the diet results in a continuous decline of the body s isotopic enrichment. The change in tracer to tracee ratio in blood corresponds directly to the fraction of the body s element inventory that has been lost and replaced. 

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An extensive literature exists on the use of radionuclides in physiological studies of terrestrial and aquatic insects. Consequently, we will refer the reader to O Brien and Wolfe (1964b) for studies that the authors classify as Digestion and absorption, Uptake and distribution of inorganic materials, Elemental turnover, Permeability of the central nervous system, and Miscellaneous studies. ... 

Radioactive indicators have found extended application in the study of the absorption, excretion, circulation, and distribution of the elements and in the study of their turnover (84). In this chapter, much of the work carried out by using radiophosphorus, radiosulfur, and radioiodine as tracers in turnover studies is discussed. Because of the importance of phosphorus in many different metabolic processes and also in view of the easy availability of radiophosphorus, its convenient half-life period, and the penetrating power of the radiation emitted, radiophosphorus has found the most extended application among the radioactive indicators. Among... 

Calcitonin therapy requires the concomitant oral administration of elemental calcium (500 mg/day). Clinical studies have shown that the combination of intranasal calcitonin salmon (200 lU/day), oral calcium supplementation (>1,000 mg/day of elemental calcium), and vitamin D (400 lU/day) has decreased the rate of new fractures by more than 75% and has improved vertebral BMD by as much as 3% annually (3). Calcitonin prevents the abnormal bone turnover characteristic of Paget s disease of the bone and has antiresorptive activity. In the presence of calcitonin, the osteoclast brush borders disappear, and the osteoclasts move away from the bone surface undergoing remodeling (36). Side effects are significantly more pronounced when calcitonin-salmon Is administered by injection and can include nausea, vomiting, anorexia, and flushing. Because calcitonin-salmon Is protein in nature, the possibility of a systemic allergic reaction should be considered. 

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