The metabolism of short-chain fatty acids in the sheep. 1. Fatty acid utilization and ketone body production by rumen epithelium and other tissues

Numerous experiments on the absorption of acetic, propionic and n-butyric acids have provided considerable information on the rates at which individual acids disappear from the rumen under the conditions of the experiment and of the concentrations appearing in the blood stream, but none of these experiments simulates normal conditions sufficiently to allow deductions to be made of the quantities of these acids normally absorbed.Recently, Johnson (1951) studied the concentrations of these acids in the rumen of fasting goats and sheep after the administration of large quantities of propionic and n-butyric acids, and came to the conclusion that butyric acid was absorbed in greater quantity than propionic acid. It is known that more butyrate can be absorbed from the rumen than can be accounted for by the butyrate entering the blood stream (Masson & Phillipson, 1951), and this is due to metabolism of butyrate by the rumen epithelium (Pennington, 1952) which in vitro is more pronounced than metabolism of propionate or acetate. The experiments described here were designed to study (a) the absorption of these three acids quantitatively by introducing a steady inflow of a solution of these acids at a suitable pH and in amounts that would maintain the concentrations in the rumen at physiological levels, and (b) to see whether the information so gained could be used to determine the rates of absorption in unanaesthetized sheep that were fasting or feeding. METHODS ExperimenkaZOne-year-old Scottish Blackface sheep, with the rumen previously cannulated, were used. The sheep were starved for 18 hr prior to the experiment to facilitate the removal of food from the rumen. The rumen was emptied and washed clean with warm saline. The sheep were anaesthetized by the intravenous injection of pentobarbitone, and the rumen was isolated in the manner described by Danielli, Hitchcock, Marshall & Phillipson (1945 ABSORPTION OF FATTY ACIDS FROM RUMEN 103The solution introduced into the rumen was Krebs's bicarbonate Ringer in which NaCl was substituted by sodium acetate, propionate and n-butyrate to give concentrations of 63 ±9, 21 i 3, and 15 ± 3 m.equiv/l. These concentrations are within the range usually found in the rumen. A similar solution, except that it contained different proportions of the three acids, was introduced into the rumen from a burette at the rate of 1 ml./min. The concentrations of acids in this solution were adjusted as the experimental series progressed until the concentrations in the rumen were steady throughout the experimental period. In this way the rate of introduction of acid served as an index to the rate of absorption. The solution in the rumen was gassed with carbon dioxide at 15 min intervals throughout the experimental period.In later experiments comparisons were made between solutions at neutral and acid pH values, and between the presence or absence of inorganic ions and carbon dioxide.Experiments on two unanaesthetized sheep were conducted in a metabolism cage. Both were accustomed to standing in th...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

The rates of absorption of acetic, propionic and n‐butyric acids

Pfander¹,

Phillipson²

1953

“…5) Table 7 it has been assumed that the traces found in the rumen have appeared in proportion to the time. Pennington (1952) It is concluded that these acidic weak electrolyte movements will give rise to hydrogen-ion movements less than -1-0 m-mole/hr, and in most cases the possible contribution of ammonia to hydrogen-ion movements is less than 1-0 m-mole/hr.…”

Section: Gaseou8 C02 Exchangementioning

confidence: 99%

The effect of absorption on the acidity of rumen contents

Ash¹,

Dobson²

1963

The role of the saliva in neutralizing the large quantities of fatty acid which are produced by the fermentations in the rumen of the sheep is well known. However, there is evidence that the absorptive properties of the reticulo-rumen epithelium also play a part in maintaining a relatively stable acidity of the rumen contents. Danielli, Hitchcock, Marshall & Phillipson (1945) observed that when fatty acid was absorbed from solutions introduced into the isolated reticulo-rumen, continual additions of acid were necessary in order to keep the pH below 6. It was suggested by Danielli et al. that at a low pH, un-ionized fatty acid was leaving the rumen more rapidly than the corresponding anion.Another mechanism involved in the neutralization of fatty acid was discovered by Masson & Phillipson (1951). These workers observed that when alkaline solutions of fatty acid were introduced into the isolated reticulo-rumen the pH drifted towards 7-3-7-8 and sometimes passed through a minimal value. Further, the appearance of total C02, mainly as bicarbonate, was closely related to the disappearance of fatty acid.The way in which the apparent interaction between fatty acid uptake and bicarbonate appearance occurs is difficult to investigate, since there are changes in seven known species of particles which may affect the pH. These are hydrogen and hydroxyl ions, carbon dioxide, bicarbonate and carbonate, ionized and un-ionized fatty acid; in addition there are unknown contributions of metabolites by the epithelium.The aim of the present work was to determine the forms in which fatty acid and bicarbonate enter and leave the solutions in the rumen. Observations were made by means of a comparatively simple system in which fatty acid was omitted from the solutions in the rumen so that information might be obtained concerning the movements of C02 and bicarbonate and thus the changes as a result of including fatty acid could be assessed. Subsequently the observations were extended to the plasma side of the epithelium. Throughout this paper the term C02 is used to describe dissolved C02 + undissociated carbonic acid; total C02 refers to C02 + bicarbonate.

“…There is, however, a clear relationship between the concentration of acetate in the rumen and the venous-arterial differences, and the fact that the relationship is not linear is interesting, for it suggests that absorption is more efficient from weak solutions than from stronger ones. The losses of acetate in vitro due to metabolism by rumen epithelium are small compared with those for butyrate and propionate (Pennington, 1952), so that a relation can be expected between these two sets of values. Poisoning ofthe rumen epithelium by exposing it to 0X002 M-mercuric chloride inhibited absorption of the anions, acetate and chloride, while absorption of the cations, potassium and sodium, proceeded unhindered.…”

Section: Discussionmentioning

confidence: 93%

The movement of potassium, sodium, chloride and water across the rumen epithelium of sheep

Parthasarathy¹,

Phillipson²

1953

Rumen liquor contains a high concentration of potassium (Parthasarathy, 1952 a), and in view of the known effects of this ion on cell membranes it was considered desirable to study the effect of solutions containing potassium in concentrations comparable to those of the rumen liquor, on the absorption of other ions and, in particular, of fatty acids. There is very little information to be found on the absorption of inorganic ions or of water from the rumen. Masson & Phillipson (1951) noted that when solutions containing no chloride were introduced into the rumen chloride appeared and they concluded it came from the blood. Scarisbrick & Ewer (1951) have reported on the irregular behaviour of inorganic phosphorus in the rumen, while recently Sperber & Hyden (1952), on the basis of experiments in which they studied the behaviour of solutions containing potassium, sodium, chloride and phosphate in a 'Pavlov' pouch of the rumen of goats, suggested that the rumen is selectively permeable to inorganic ions.The question whether water is absorbed from the rumen has never received close attention and, as there are good reasons to believe that water is absorbed from the digesta before they reach the abomasum (Garton, 1951; Masson & Phillipson, 1952), particular attention has been given to the volume changes that have occurred during the course of these experiments. The results show clearly that the rumen epithelium is readily permeable to water, but further work is needed to establish the direction of the flow under normal conditions. Some evidence has been found to support the contention of Sperber & Hyden, but the support so far is qualified. No evidence has been obtained to show that fatty acid absorption is affected by the ions under investigation. METHODSSheep previously fitted with an ebonite rumen cannula were used in all experiments, and the surgical techniques for the isolation and emptying of the rumen and for the withdrawal of blood are identical with those previously described (Masson & Phillipson, 1951 (McAnally, 1944) was added to the sample, as this prevents the appearance of chloride in the distillate. The modification of the McClendon procedure, the accuracy of which is given by Kiddle, Marshall & Phillipson (1951), was used for total volatile acid in blood. The freezing-point of rumen liquor and of blood serum was used as an indirect measure of the osmotic pressure of these fluids. The procedure described by Findlay (1932) was followed. Normally fed sheep fitted with rumen cannulae provided rumen liquor. The samples were drawn rapidly without suction, filtered rapidly through gauze and stored under liquid paraffin. Blood was withdrawn from the jugular vein by a syringe and transferred to a centrifuge tube under liquid paraffin. The serum so obtained was used for the determination of the freezing-point. The effect of loss of carbon dioxide or rumen liquor by exposure to the air was examined by determining the freezing-point after exposure and then again after re-equilibration with a mixture of 60% CO2...