Dating physiological changes

PBPK and classical pharmacokinetic models both have valid applications in lead risk assessment. Both approaches can incorporate capacity-limited or nonlinear kinetic behavior in parameter estimates. An advantage of classical pharmacokinetic models is that, because the kinetic characteristics of the compartments of which they are composed are not constrained, a best possible fit to empirical data can be arrived at by varying the values of the parameters (O Flaherty 1987). However, such models are not readily extrapolated to other species because the parameters do not have precise physiological correlates. Compartmental models developed to date also do not simulate changes in bone metabolism, tissue volumes, blood flow rates, and enzyme activities associated with pregnancy, adverse nutritional states, aging, or osteoporotic diseases. Therefore, extrapolation of classical compartmental model simulations... 

Radiocarbon years are calibrated from determinations of the 14C activity and stable isotopic carbon ratios of dendrochrono-logically dated tree rings [4]. The stable isotope data are required to normalize the dates to average wood with 613C value of -25 per mil (13C/12C fractionation relative to PDB reference standard). Photosynthetic and other plant physiological processes may produce differential isotopic fractionation between species, within the same species in different localities and even within the same tree under changing environmental conditions. 

Fatty Acids Physiological and Behavioral Functions edited by David I. Mostofsky, Shlomo Yehuda, and Norman Salem, clearly exemplifies the goals of iht Nutrition and Health series. In fact, this volume is surely ahead of the curve with regard to awareness of the importance of fatty acids in virtually every aspect of human health and disease prevention. Two fatty acids are considered essential nutrients for humans linoleic and linolenic acids. Thus, there is no question about the importance of dietary intake of adequate levels of these essential nutrients. However, the story of the changes in our food supply and the consequences of consumption by us, as well as our farm animals, of foods that no longer have the same balance of these essential fatty acids had yet to be captured in one authoritative, up-to-date volume until now. 

A large variety of protein methylation reactions occur in nature. It appears that the function of many of these reactions is to create new types of residues that complement the twenty amino acid residues available from ribosomal synthesis. To date, it has been difficult to address the question of what specific advantages the methylated residues impart to the protein, especially in cases where methylation does not occur and where there is little or no gross change in the physiology of these cells or organisms. It is tempting to speculate that many of these modifications may be only crucial to the cell under certain circumstances—nutrient deprivation or oxidative stress for example. 

There are many vital cellular processes, such as membrane fusion, which must involve, if only locally and transiently, changes in lipid phase state. To date, however, little attention has been paid to the dynamics of lipid phase interconversions. If, indeed, such changes are physiologically relevant, they must occur on a time scale comparable with those taking place in vivo. Thus, there is a need to establish the kinetics of lipid phase transitions. In addition to the kinetics, little is known about the mechanism of lipid phase transitions. Such information is integral to our understanding... 

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