Intake retention functions

Based on data on these dial painters from the 1985 listing of radium cases studied at the Argonne National Laboratory (Gustafson and Stehney 1985) Rundo et al. (1986) have estimated that the lowest total intake level of radium associated with a malignancy was 60 pCi (2,222 kBq) or 1.03 p Ci/kg (38 kBq/kg) based on an estimated 58 kg body weight for a woman. These estimates are based on current radium body content modified by the Norris retention function (to account for the decrease in body radium content with time since exposure) and an estimate of radium-228 from measurements of radium-226 and the known or presumed ratios of these isotopes in the materials to which these persons were exposed (Rundo et al. 1986). 

Direct or indirect measurements provide information about the amount(s) of radionuclides present in the body, in parts of the body such as specific organs or tissues, in a biological sample or in a sample from the working enviromnent. The first use of these data is likely to be an estimation of the intake of the radionuclide by the worker. Biokinetic models which describe body and organ contents, and activity in excreta, as a function of time following intake, and exposure models which relate intake to workplace conditions, are used for this purpose. Alternatively, measurements of activity in the body can be used to estimate dose rates directly. The calculation of committed doses from direct measurements still involves the assumption of a biokinetic model if sufficient measurements are not available to determine retention functions. 

The structural analysis of membrane-associated peptides comprises two steps (a) the elucidation of the three-dimensional fold of the peptide and (b) the determination of the membrane-peptide interface. We will use our results gained for the 36 amino acid residue neuropeptide Y (NPY) [83] to demonstrate the approaches that can be used. NPY regulates important pharmacological functions such as blood pressure, food intake or memory retention and hence has been subject of many investigations (for a review see Ref. [84]). It targets the so-called Y receptors that belong to the class of seven transmembrane receptors coupled to G-proteins (GPCRs). 

Food Applications. On the basis of intake, sucrose is the leading food additive (2). Its principal contribution to food is sweetness. However, it provides many other functionalities, eg, body, mouthfeel, texture, and moisture retention. Cereals and baked goods are the leading consumers of sucrose, followed closely by confectionery products (36). 

The metabolism and tissue distribution of cesium-137 were studied in rats injected intraperitoneally and sacrificed 1-300 days postinjection. In a chronic study, rats were administered cesium-137 in their drinking water daily. In the acute study, with the exception of the brain, muscle, and total animal, all tissues showed retention curves resolvable into three exponential components with half-lives of 1.5-2, 5-8, and 15-17 days. Retention in muscles was resolvable into a two-exponential function with half-lives of 8 and 16 days. In the chronic study, the highest equilibrium cesium-137 concentrations, 10% of the average daily intake per gram, occurred in the muscle. The authors concluded that the muscle should be considered the formal critical organ for cesium-137. 

An excessive intake of water or excessive retention of water without equivalent intake or retention of sodium can result in hyponatremia, particularly if the mechanisms that control fluid and electrolyte balance are impaired. Altered function of an organ or the hormones that regulate sodium and water (e.g., kidney, pituitary gland and hypothalamus [aldosterone] or adrenal gland [ADH] as well as ANP from the right atria) can cause excess loss of sodium or retention of water and thus can result in hyponatremia. 

The slope of the line relating retention to intake is a measure of the efficiency of ME utilisation. For example, if the ME intake of an animal was increased by 10 MJ and its retention increased by 7 MJ, then the efficiency of utilisation of ME would be calculated as 7/10 = 0.7. (Conversely, the heat increment would be calculated as 3/10 = 0.3 of the ME.) These efficiency values are conventionally called k factors, with the letter k carrying a subscript to indicate the function for which ME is being used.The commonly used k factors are shown in Box 11.6. 

Blintz, G. L. 1969. Sodium-22 retention as a function of water intake by Citellus lateralis, pp. 45-52. In Physiological Systems in Semiarid Environments (C. C. Hoff and M. L. Riedesel, eds.). University of New Mexico Press, Albuquerque. 

Similar mathematical treatment of available nitrogen balance data (21) for the first 90 days of life of the full-term infant of normal birth weight (Fig. 1) indicates that an intake of 400 mg. of human milk nitrogen is required for normal nitrogen retention which again appears to be a function of weight rather than age (40). An approximation of the specific amino acid needs of the infant of this age group based on the mean... 

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