R.L. Baldwin

The synthesis of models to describe metabolism and its integration.

The wide range of metabolic, nutritional and physiological information which must be integrated in analyses of animal metabolism and function indicates that modelling techniques can be utilized and contribute to the research process. Advantages gained through the use of modelling techniques in support of research include evaluations of available concepts and results for adequacy as quantitative and dynamic explanations of the behaviour of complex (metabolic, physiological) systems, evaluation of alternate hypotheses for probable adequacy, interpretation or extension or both of available information, and identification of critical experiments. Achievement of these objectives requires a close interaction of modelling and experimental analyses. Additional requirements imposed by these objectives are that the elements of research models represent specific biological entities (model must be causal), that the basic models be firmly based on established principles and contain no hypothetical elements, and that numerical inputs to the model derive directly from experimental measurements. Emphasis in developing this presentation was placed upon illustration of these principles and objectives of research modelling. Examples were drawn from three ongoing modelling analyses; animal metabolism, animal growth, and tissue metabolism. Models of whole animal metabolism The development of early models of animal metabolism required extensive searches of the literature and summarization and integration of a wide range of information. Results utilized included estimates of organ weights and energy expenditures, extracellular and intracellular pool sizes of metabolites, nutrient absorption, turnover and utilization rates, and oxidation rates of metabolites (Smith, 1971; Smith et al. 1975). Mathematical representations of tissue metabolism require consideration of energy requirements for basal metabolism and for variable biosynthetic and work functions, affinities of tissues for metabolites, biosynthetic and oxidative capacities of tissues and specific regulatory mechanisms. A generalized equation set for a typical tissue expressed in a modified FORTRAN format follows: DADP=ATPUSE- METOX:SATP,