Utilization of amino acids by the isolated perfused sheep liver

Standing on giant shoulders: a personal recollection of the lives and achievements of eminent animal scientists 1965–2015

This article is a compilation of pieces that are part biographical sketches and part personal recollections of 18 scientists with whom the author was acquainted in three continents over almost 50 years. The subjects, from Australia, the United States and the United Kingdom, will be recognisable to many in the field, especially more experienced scientists. For younger scientists, the article also is intended to put a human face on a generation of famous researchers who otherwise would be familiar only as somewhat anonymous authors of classic papers and reviews.

Changes in mRNA expression for gluconeogenic enzymes in liver of dairy cattle during the transition to lactation

The objective of this study was to profile phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) mRNA expression in the liver of dairy cattle during the peripartum transition and determine changes in abundance of these mRNA in response to protein fed during the prepartum period. Thirty-eight multiparous Holstein cows were fed diets containing either 12% crude protein (CP) and 26% rumen undegradable protein (RUP), 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry-matter basis beginning 28 d before expected calving. After calving, all cows were fed a common diet through 56 d in milk (DIM). Northern analysis of RNA from liver biopsy samples obtained on days -28, -14, +1, +28, and +56 relative to calving indicated that PC and PEPCK mRNA expression were responsive to onset of lactation but not to prepartum protein or RUP concentration. Abundance of PEPCK mRNA was similar at -28, -14, and +1 DIM but was elevated by +28 and +56 DIM relative to precalving levels. Liver PC mRNA abundance was elevated on +1 DIM, remained elevated through 28 DIM, and declined to precalving levels by 56 DIM. The activity of PC enzyme was correlated (r2 = 0.89) with PC mRNA abundance. The data demonstrate increased abundance of PC mRNA during the early transition period followed by increased abundance of PEPCK mRNA during the postpartum period and suggest increased potential metabolism of lactate, pyruvate, and amino acids that contribute to the liver pyruvate pool.

Amino acid flux across the gastrointestinal tract and liver of calves

Fluxes of peptide and of free AA in plasma and blood cells were quantified across the gastrointestinal tract and liver of six growing Holstein steers (136 kg). Calves were fed hourly, and blood was obtained simultaneously from the aorta, protal vein, and hepatic vein cannulas on 1 d between d 9 and 12 postsurgery and again following 72 h without feed. Blood flow was determined by p-aminohippuric acid infusion. Peptide AA accounted for the greatest concentration of AA in arterial blood of all calves. There was a net flux of free AA in plasma across the tract, and lack of feed reduced the magnitude of the flux. Glutamine and glutamate were the only free AA in plasma with a negative flux across the tract in fed calves. Alanine accounted for over 14% of the total tract flux of free AA in plasma of fed calves. Hepatic removal of free AA in plasma increased after feed deprivation. Flux of free AA in blood cells was negative across the tract of fed calves but to a lesser extent in unfed calves. The hepatic flux of free AA in blood cells offset the negative tract flux, thus resulting in no net splanchnic output of free AA in blood cells by calves. Peptide AA flux across the tract was 2.5 times (fed) to 7.2 times (unfed) greater than free AA flux. Net splanchnic output of peptide AA was 7 times the magnitude (738 vs. 92 g/d) of the net splanchnic output of free AA in plasma. Peptides with molecular mass from 500 to 1500 Da accounted for the largest flux of peptide AA across the tract. Quantitatively, peptides appeared to be involved extensively in interorgan transport and may be a substantial form of absorbed AA in calves.

Preparation and biochemical characterisation of isolated parenchymal cells from adult sheep liver

1. A simple procedure for the isolation of morphologically intact, metabolically viable sheep liver parenchymal cells is described in detail. 2. The method is based on the initial treatment of fresh liver slices with collagenase and hyaluronidase. 3. The cell preparation was studied with respect to membrane permeability, potassium content, ATP/ADP ratio, adenylate content, and gluconeogenic capacity with respect to various substrates. 4. Data are present with respect to the distribution of phosphoenolpyruvate carboxykinase in isolated cells and whole sheep liver. 5. The results are compared, where possible, with data currently available from isolated perfused sheep liver and multi-catheterised animals.