ALTERNATIVE MODELS FOR ANALYSES OF LIVER AND MAMMARY TRANSORGAN METABOLITE EXTRACTION DATA

Alternative models for analyses of liver and mammary transorgan data w ere formulated and fitted to liver and mammary data sets respectively. The models considered metabolite inputs to and effluxes from an extra cellular pool. In general, fits were greatly improved over previous ef forts using other models (Miller et al. 1991a; Hanigan et al. 1992; Wr ay-Cahen et al. 1997). Errors of prediction were generally less than 1 5 % for liver and less than 20 % for mammary glands. With the possible exception of glutamine for the udder, all metabolites exhibited linea r responses to extracellular concentrations within the observed ranges of inputs. However, prediction biases were evident for beta-hydroxybu tyrate, acetate, and propionate by liver and for arginine, histidine, citrulline and glycerol by mammary tissue. These biases were hypothesi zed to be caused by the existence of additional regulatory complexity. With the exception of histidine, parameter estimates for essential am ino acid removal by liver were 2-3-fold lower than for mammary gland. Infusion of an amino acid mixture into the mesenteric vein did not alt er parameter estimates for removal of amino acids by the liver. Treatm ent of cows with bovine somatotropin resulted in changes in mammary pa rameter estimates for aspartate, glutamate, leucine, phenylalanine, gl ucose, and glycerol.