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Title:Influence of Homeorhetic State on Ruminant Metabolism and Substrate Selection for Hepatic Gluconeogenesis
Author(s):Overton, Thomas Richmond
Doctoral Committee Chair(s):Drackley, James K.; Clark, Jimmy H.
Department / Program:Animal Sciences
Discipline:Animal Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Molecular
Abstract:We hypothesized that the contribution of amino acids to hepatic gluconeogenesis would increase when glucose demand was increased in ruminants. Our first approach was to establish a sheep model for increased glucose demand. Four wethers injected with excipient or.5, 1.0, or 2.0 g/d of phlorizin excreted an average of 0,72.7, 97.9, and 98.5 g/d of glucose into the urine. Wethers injected with 1.0 g/d of phlorizin excreted approximately 50% of their probable daily glucose production into their urine and adapted by 24 h after the first injection. Phlorizin-induced changes in plasma variables suggested increased gluconeogenesis from amino acids. In experiment 2, isolated hepatocytes from 10 Dorset wethers injected with excipient or 1.0 g/d of phlorizin for 72 h were used to determine the effects of increased glucose demand on conversion of (1-$\sp{14}$C) propionate and (1-$\sp{14}$C) alanine to CO$\sb2$ and glucose. Phlorizin tended to increase conversion of substrates to CO$\sb2.$ Conversion of (1-$\sp{14}$C) alanine to glucose was increased more by phlorizin treatment than that of (1-$\sp{14}$C) propionate (285 vs. 166% of controls). Phlorizin increased estimated V$\sb{\rm max}$ for conversion of substrates to CO$\sb2$ and tended to increase estimated V$\sb{\rm max}$ for conversion of substrates to glucose. Addition of 2.5 mM NH$\sb4$Cl in vitro decreased conversion of (1-$\sp{14}$C) propionate to glucose and CO$\sb2$ but had little effect on conversion of (1-$\sp{14}$C) alanine. These data suggest that potential utilization of amino acids for gluconeogenesis increases when glucose demand is increased. In experiment 3, thirty-six Holsteins were fed high grain or high fat diets for restricted or ad libitum intake prepartum, and then all fed a lactation diet postpartum. Liver slices determined in vitro conversion of (1-$\sp{14}$C) propionate and (1-$\sp{14}$C) alanine to CO$\sb2$ and glucose. Conversion of substrates to products was increased at 1 and 21 d postpartum compared with 21 d prepartum and 65 d postpartum. Conversion of (1-$\sp{14}$C) propionate to products was greater than conversion of (1-$\sp{14}$C) alanine; however, conversion of (1-$\sp{14}$C) alanine to glucose at 1 and 21 d postpartum was 198% and 150%, respectively, of that at 21 d prepartum and conversion of (1-$\sp{14}$C) propionate to glucose at 1 and 21 d postpartum was 119% and 129%, respectively, of that at 21 d prepartum. The ratio of 3-methyl histidine to creatinine in urine was increased markedly postpartum until 21 d postpartum. Results indicate that amino acids are more important as gluconeogenic substrates during the first 3 wk of lactation than at other stages of the lactation cycle. Furthermore, prepartum manipulation of dietary energy has more influence on hepatic propionate metabolism than amino acid metabolism.
Issue Date:1998
Description:145 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.
Other Identifier(s):(MiAaPQ)AAI9904557
Date Available in IDEALS:2015-09-25
Date Deposited:1998

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