Lower Fatty Acids in the Intermediary Metabolism of Sheep

Abstract

Acetic, propionic and butyric acids which ai'e formed by bacterial fermentation in the paunch of ruminants assume an import^aiit role in the metabolism of these animals (Marston, 1939(Marston, , 1948 PhiUipson, 1947 PhiUipson, , 1948. Although the greater part of the energy requirements of the sheep are met by lower fatty acids which arise in this way by microbial dissimilation of carbohydrates, the capacity of the individual acids to provide useful energy to the animal probably differs widely (Marston, 1948). Thus, iu view of tlie "relatively large amounts of acetate and propionate that are dealt with each day by the sheep, the metabolic routes of these compounds are of considerable interest.The work of Ringer (1912) and of Deucl, Butts, Hallmau and Cutler (1935) revealed the glucogenic nature of propionate when administered to dogs, and this is also true for the phlorhizinised sheep (PhiUipson, 1947;Jarrett, 1948). Reid (1950) has shown that the hypoglycaemia produced by injection of insulin is relieved by propionate.The metabolic effect of butyric acid ha.s usually been considered in relation to the metabolism of fat and to the production of ketone bodies (Stadie, 1946). However, there is evidence to indicate that carbon atoms of butyrate may be incorporated into liver glycogen (Lifson, Lorber, Sakami and Wood, 1948).Acetate is known to be an important source of carbon atoms for a number of biological syntheses (Bloch, 1947), and although observations of the fate of acetic acid in phlorhizinised animals (Ringer and Lusk, 1910;Deuel and Milhorat, 1928;Jarrett and Potter, 1950a) indicate that acetate is not glucogenic, Lorbor, Lifson and Wood (1945) suggest that carbon atoms from acetate may be incorporated in the glucose molecule. It seems probable, however, that while glucose cannot be formed from acetate itself, their metabolism is interlinked.As a part of an investigation of intermediary metabolism of fatty acids in the sheep, the fate of acetate and butyrate in relation to propionate when injected into the blood stream has been examined. A group of twelve Merino ewes ael. 3-5 years were confined to peii9 and fed on chaffed wheaten hay and lucerne. During the period of the experiment the animals were kept in metaboUsm cages and food offered for 3-5 hours during the afternoonB.The concentrations of ketone bodies, of sugar and of lactic and iiyruvic acids were determined in the blood of seven of the sheep concurrently with those of the volatile aeids subsequent to tlie intravenous injection of 5 mM/kg. of acetic or propionic acids or of a mixture of the two. These solutions were neutralized to pH 7-0 with caustic soda; the volume administered was 120 ml. for the individual acids aniT 240 ml. for the mixture. Similar observations were carried out on five of the sheep after the injection of bntyric acid. A few experiments were also performed using 2-5 luM/kg. instead of the larger amount of acid. In addition, observations were made following the injection of a solution of hypertonic saline or of a solution o...

The heat increment of steam-volatile fatty acids in fasting sheep

“…Jarrett, Potter & Filsell (1952), Johnson (1955) (1955) have shown that the rumen epithelium is a major site for the conversion of butyric acid to ketone bodies. The finding of a smaller, but nevertheless significant, rise in blood ketones with acetic acid is in agreement with the results of Jarrett & Potter (1950), Jarrett et al (1952) and Clark & Malan (1956). All the above-mentioned workers have demonstrated the antiketogenic nature of propionic acid.…”

The Effect of Glucose on Blood Pyruvate in Sheep

“…The concentration of pyruvate in the blood of normal rabhits was found to agree closely with that reported previously (Lu, 1939), but the normal value for adult sheep was found to he much lower than that observed hy Austin (1947). However, this difference might well he attributed to the different experimental conditions, as it is clear that a state of activity affects the pyruvate concentration in the hlood: to obtain reasonably comparable results it is essential that the animal be maintained in a thoroughly placid condition (Jarrett, Potter and Filsell, 1952). The technique of intravenous cannulation used in this study assisted considerably towards this end.…”

“…which resulted in an average rise of 4 mg./lOO ml. No alteration followed an injection of sodium acetate (Jarrett, Potter and Filsell, 1952).…”

“…In view of the nature of the intermediary metabolism of the adult ruminant (Marston, 1939;McCandless and Dye, 1950;Jarrett and Potter, 1953), and of the apparent similarity in some respects of a young lamb and a non-ruminant (Jarrett and Potter, 1952), the effect of an injection of glucose on the blood pyruvate level in the young lamb and the adult sheep was compared.…”

BLOOD CHEMISTRY AND GASTRO‐INTESTINAL CHANGES IN THE DEVELOPING RED KANGAROO (MEGALEIA RUFA, DESMAREST)

“…VFA concentrations in whole blood were estimated by the method of Jarrett, Potter and Filsell (1952), using phenol red to detect the end-point of titration.…”