Absorption Of Organic Acids Research Articles

The Electrochemical Reduction of Organic Acids on Anatase-Type TiO2 Nanoparticles – a Theoretical Approach

The electrochemical reduction of organic acids on anatase-type TiO2electrode has been recently reported by Yamauchi [1]. Such an electrochemical reaction has a potential to produce alcohol products with high selectivity and efficiency, which can be used as alternative fuel. However so far the reaction is reported only for oxalic acid, and other acids like acetic acid cannot be reduced. This reaction raise many questions, including the mechanism or the electrochemical steps as well as the role of the anatase electrode. We used Density Functional Tight Binding (DFTB ) method to study the interaction between organic acids and possible intermediates of the reduction reaction. For the simulation, models of the (101) surface of anatase as well as nanoparticle models were also used. TiO2 nanoparticles, unlike surface slab models, always have a strong dipole moment, which interfere with absorption of organic acids as well as the solvent water molecules. The morphology of the nanoparticles has also a strong influence on the bandgap of TiO2: calculations showed an approx. 0.5 eV smaller gap for the nanoparticles. The decrease of the gap were mostly due to the significantly lower LUMO energy levels when they are compared to surface models (Figure 1). These low energy LUMO levels are due to edge effects and are expected to play an important role in the electrochemical reduction over these nanoparticles. Calculations showed very strong absorption of the acids on the anatase models (in order of 150 kJ/mol). Such a strong absorption of the carboxyl group may actually protect it from the reduction. We hypothesized that one of the carboxyl group of oxalic acid acts as an anchor, while the reduction reaction is taking place mostly on the other side of the molecule. This would also explain why ordinary carboxylic acids like acetic acid cannot be reduced under the same conditions. Reference: [1] R. Watanabe, M. Yamauchi, M. Sadakiyo, R. Abe and T. Takeguchi, Energy Environ. Sci., 2015, 8, 1456–1462. Figure 1

Characterization of pH dependence in organic acid absorption with non-reactive and reactive polymers for application in two-phase partitioning bioreactors

Strategies for extracting organic acids from aqueous solutions using polymeric absorbents are demonstrated and discussed in the context of two-phase partitioning bioreactor (TPPB) design. Experimental data and material balances for the uptake of butyric acid and benzoic acid by a poly(ether-block-amide) copolymer (Pebax 2533) establish the inherent limitations of unreactive absorbents for organic acid bioprocesses that operate at near-neutral pH. Improvements to TPPB performance are achieved by lowering pH temporarily with CO2 to enhance acid absorption, and removing the solute-rich polymer before restoring pH to fermentative values by releasing the CO2 pressure. Butyric acid removal by Pebax 2533 improved from 3% to 40% upon acidifying a pH 6 solution with 60bar of CO2, while benzoic acid absorption increased from 1% to 80% using this pressure manipulation technique. A reactive extraction approach involving a newly-synthesized amine functionalized hydrogel is also described wherein acid/base reaction equilibrium governs the extent of solute uptake. Copolymerization of 2-(dimethylamino)ethyl acrylate (DMAEA) and trimethylolpropane triacrylate (TMPTA) yielded a thermoset material with sufficient basicity to remove 80% of both butyric and benzoic acid from aqueous solution using just 1wt% polymer relative to the aqueous phase mass.

Ruminal Acidosis in Beef Cattle: The Current Microbiological and Nutritional Outlook1,2

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.

Managing Acidosis in Feedlot Cattle

The cattle feeding business in the United States has evolved to an intensively managed system using grains as the primary source of energy. Grain feeding is common throughout the cattle feeding regions of the United States because the cost per unit of energy is often cheaper with grain compared with other feedstuffs available for beef cattle. In addition, grains are easier to store, handle, process, mix and deliver in rations compared with bulky, lower energy forage type feedstuffs. Consumers also prefer the taste and flavor of grain-fed beef compared with other alternatives.
 Acidosis is one of the most important nutritional disorders in feedlot cattle today and is caused by a rapid production and absorption of organic acids and endotoxins from the rumen when cattle over consume grain (starch) or sugar in a short period of time. Acidosis is an array of stresses and is not confined to a single symptom such as ruminal pH. The previous definition is a collective term for several associated facets and includes the effects of organic acid production, ruminal pH, salivary flow, rate of passage, starch fermentation, feed intake and others. Ruminal acidosis often leads to metabolic acidosis in feedlot cattle. Acidosis is difficult to measure and diagnose in feedlot cattle. Even in metabolism studies designed to measure the effects of acidosis, it is difficult to research because as ruminal pH declines, cattle adjust by decreasing feed intake and altering their consumption patterns to help diminish the deleterious effects of acidosis.
 Acidosis is not one disorder, but a continuum of degrees. Effects of acidosis can be slight as a .25 lb/ day decrease in feed intake, or as severe as the death of an animal. Brent2 attributed founder, polioencephalomalcia (PEM) and ruminitis to acidosis in feedlot cattle. Sudden death syndrome, reduced feed intake, reduced absorption, liver abscesses, grain bloat and clostridial infections have been added to the list of acidosis related problems. Acidosis is not the only nutritional disorder that can occur in beef cattle fed high-grain diets, but may be a contributing factor to many of the diagnosed nutritional disorders that are currently observed in feedlot cattle. Many of the management recommendations that feedlot nutritionists make on a daily basis are to reduce the incidence and severity of acidosis. Because acidosis is not simply one disorder we generally separate acidosis into acute or subacute situations. The actual ruminal pH where subacute acidosis becomes acute is difficult to define and probably not very important. Additionally, the actual ruminal pH where an individual animal experiences subacute acidosis may be equally less important because of animal-to-animal variation.

Starch utilization by ruminants: from basics to the bunk.

Starch is the major energy component of grains. Wheat contains 77% of DM as starch, corn and sorghum contain 72%, and barley and oats contain 57 to 58%. In vitro systems have provided valuable data on kinetic aspects of starch digestion. Molecular biological techniques have provided a clearer picture of the ruminal microbial milieu. Proportions of starch fermented in the rumen can be predicted satisfactorily for a variety of grains and processing methods. Compared with dry rolling, steam processing (flaking or rolling) increases ruminal digestibility of starch (percentage of intake) from 52 to 78% for sorghum, from 75 to 85% for corn, and six percentage units or less for other grains. Recent research provides new insight into pancreatic function and intestinal glucose transport systems. The capacity to digest starch in the intestine ranges from 45 to 85% of starch entering the duodenum, with that capacity apparently limited by the supply of pancreatic amylase. There is evidence that amylase secretion may be enhanced by increasing duodenal entry of protein. Capacity for active transport of glucose across of gut wall does not seem to limit the amount of starch digested that is absorbed as glucose. For ruminants eating medium- to high-concentrate diets, about 30% of their total glucose need comes from glucose absorption, 50% from organic acid absorption (substrates for hepatic gluconeogenesis), and 20% from other sources. When glucose absorption from the gut increases, ruminants generally adjust (decrease) gluconeogenesis to meet their need; that need is directly linked to DE intake. In terms of overall ME yield, grain starch is best used when it is fermented in the rumen. However, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.

Colonic mucosal tissue energetics and electrolyte transport in dogs fed cellulose, beet pulp or pectin/gum arabic as their primary fiber source

Fifteen adult beagle dogs were used to assess the effects of dietary fiber (cellulose, beet pulp and pectin/gum arabic) on the canine colonic mucosal DNA content, energetic activity and electrolyte transport systems. The fiber sources were selected according to their relative colonic fermentability (i.e. cellulose is limited, beet pulp is moderate and pectin/gum arabic is highly fermentable). Mucosal tissues of dogs fed the cellulose diet had significantly more DNA (ug/mg of tissue) than that of those fed the beet pulp or pectin/gum arabic fiber sources. However, dogs fed the pectin/gum arabic diet had significantly greater mucosal energetic activity (umol O 2 · g −1 · min −1) per unit DNA than did the other two fiber sources. While the proportion of organic acid absorption was not statistically different among treatment groups, dogs fed the beet pulp absorbed more acetate than propionate or butyrate. However, the feeding of pectin/gum arabic resulted in greater butyrate absorption. The results of this study in conjunction with three earlier studies clearly suggest that; feeding dogs beet pulp (a moderately fermentable fiber source) provided not only an modest and appropriate colonic SCFA concentration but also the more optimal acetate, propionate and butyrate fermentation/absorption pattern, when compared to cellulose and pectin/gum arabic.

Net portal absorption of lactate and volatile fatty acids in steers experiencing glucose-induced acidosis or fed a 70% concentrate diet ad libitum.

Five crossbred steers (347 kg) were surgically fitted with rumen fistulae, hepatic portal, abdominal aorta and mesenteric catheters to measure organic acid absorption from the gut during acute [intraruminal glucose, 12 g/kg body weight (G)] or subacute [ad libitum 70% concentrate diet (C)] acidosis. Samples were taken at time 0, then every 2 h for 48 h after a switch from an alfalfa diet to C, or dosing with G. Steers receiving C received G 1 wk later so that five steers provided four observations/treatment. Blood flow rates were determined by infusion of para-amino hippuric acid (PAH) and averaged 767.8 and 712.5 liters/h for C and G, respectively. Animals consuming C averaged 13.6 kg dry matter from 0 to 24 h and 1.5 kg from 24 to 48 h. Rumen pH declined to 4.2 for G compared with 6.0 for C. Blood pH and HCO3 showed only slight depressions for G from 16 to 26 h, the period of lowest rumen pH. Rumen L-lactate concentration averaged 53.4 mM (peak 77 mM) and 2.1 mM for G and C, respectively. Rumen D-lactate concentration averaged 30.2 mM (peak 47 mM) for G and 1.2 mM for C. Net portal absorption of L-lactate averaged 96.6 and 164.4 mmol/h, whereas that of D-lactate averaged 10.5 and 71.8 mmol/h for C and G, respectively. Mean net portal volatile fatty acid absorptions were 442.8, 192.1, 53.8, 5.3 and 10.4 mmol/h (C) and 100.0, 47.2, 9.4, .98 and .78 mmol/h (G) for acetate, propionate, butyrate, isobutyrate and isovalerate, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Digestion and Absorption of Nutrients by Beef Heifers Fed a High Concentrate Diet

A replicated, 3 × 3 Latin square design was used to evaluate effects of calculated metabolizable energy (ME) intake by beef heifers on apparent digestibility (AD), retention and net absorption (portal-arterial plasma concentration times protal plasma flow measured by dye dilution) of various nutrients. Six Hereford × Angus heifers (295 ± 4 kg) with catheters in portal and mesenteric veins and iliac artery were fed once daily a high concentrate, pelleted diet to provide 84, 157 or 225 kcal ME/kg0.75. Linear (P < 0.05) responses to increased ME intake included AD of dry matter (84.9–76.7%); AD of digestible energy (DE) (83.4–74.3%); AD of nitrogen (N) (70.5–62.1%); N retained (-6.3 to 25.6 g/day); portal blood flow (444–782 liters/hour); and net absorption of volatile fatty acids (VFA) (311–795 mmol/hour), L-lactate (62.5–118.4 mmol/hour), and urea-N (-19.9 to -51.4 mmol/hour). Net ammonia-N absorption increased linearly (P < 0.10) from 35.6 to 43.8 mmol/hour as ME intake increased. Net glucose absorption was negative at low intake, but tended to increase to positive values as intake increased. Moles of acetate (46.3), propionate (29.3) or 4-carbon VFA (6.3) per 100 mol of net organic acid (VFA plus L-lactate) absorbed were similar among intake levels. Intake level did not affect proportions of DE intake (0.43) or calculated ME intake (0.46) accounted for by net organic acid absorption.

Effect of organic acid absorption on bicarbonate transport in rat colon.

The absorption of organic anions and the influence of these anions on the movement of HCO3- were studied in vivo in rat colon using a perfusion technique. The absorption of short chain fatty acids (SCFA's) such as acetate, propionate, and butyrate was much greater than that of succinate or lactate. With increasing initial concentration of SCFA up to 100 mmol . 1-1, SCFA absorption increased linearly in correspondence with HCO3- appearance. Final pCO2 level of the perfusion solution with SCFA was the same as the plasma level. Among the SCFA's, no significant differences in absorption or their effects on HCO3- appearance were observed. The presence of Na+ stimulated SCFA absorption, and the maximum value was obtained at more than 100 mmol . 1-1 of Na+. These results suggest that a specific system for HCO3- secretion activated by SCFA exists in the colon, and that this system may control the intraluminal pH by the alkalization of intestinal contents.

ORGANIC ACIDURIA FOLLOWING EXTENSIVE SMALL BOWEL RESECTION

Routine screening has identified two patients with striking organic aciduria after extensive small bowel resection. JK, a 5 ½ yo male, underwent resection of all but 21 cm of small bowel at 3 days of age because of necrosis secondary to midgut volvulus and subsequently has had recurrent acidemic episodes. TK, a 5 yo female, was left with 15 cm of jejunum following mesenteric artery thrombosis at 15 months. Both have experienced episodes of progressive abdominal distention, colonic ileus, and CNS depression. Urinary lactate (JK only), glutarate, propionate, β-hydroxyphenylacetate and β-phenyllactate were elevated. White blood cell glutaryl-CoA dehydrogenase activity in JK was normal. Serum prostaglandin E and F were significantly elevated in JK. Absorption of organic acids from stool has been reported and these patients illustrate that this may become quantitatively significant following small bowel resection. The data also suggest that the addemia of short bowel may not be solely due to bicarbonate wasting. Our patients demonstrate that gastroenterologic disorders constitute a previously unrecognized etiology to be differentiated from inborn enzymatic errors associated with glutaric aciduria. Dietary restriction, oral bicarbonate, catharsis, and inhibitors of prostaglandin synthesis may play a role in treatment of this disorder.

Pulmonary Absorption Studies Utilizing In Situ Rat Lung Model: Designing Dosage Regimen for Bronchial Delivery of New Drug Entities

The absorption of 7‐methylsulfinylxanthone‐2‐carboxylic acid, 7‐(methylthio)xanthone‐2‐carboxylic acid, and their sodium salts from the respiratory tract of anesthetized rats was studied after intratracheal administration of 0.1ml of a solution or suspension containing the drug. At various times after administration, the lungs and trachea were removed and assayed radiochemically for unabsorbed drug. Sodium 7‐(methylthio)xanthone‐2‐carboxylate from solution was absorbed approximately 20 times faster than sodium 7‐methylsulfinylxanthone‐2‐carboxylate from a solution. The absorption from solutions was three to four times faster than the absorption from suspensions. For inhalation aerosol dosage forms intended for prophylactic use, the drug entity with slower systemic absorption probably would be more desirable than the drug entity with rapid absorption. Rapid systemic absorption following inhalation of powder or liquid aerosols would lead to more frequent dosing if the biological activity is related to the drug concentration in the tracheobronchial tissues. Therefore, the powder or liquid inhalation aerosols of organic acids rather than the corresponding sodium salts may be preferable for designing a dosage regimen. However, if the dosage form is intended for utilizing the bronchodilator activity of the compound, the drug entity with rapid absorption is more desirable. Therefore, in the treatment of asthmatic attacks, liquid or powder inhalation aerosols of the sodium salt of the rapidly absorbing drug entity are preferable. The absorption rates were directly proportional to concentration when the initial concentration of sodium 7‐methylsulfinylxanthone‐2‐carboxylate was varied over a 333‐fold range. The effect of the pH of the drug solution administered intratracheally to the rat lung indicated a sharp increase in the pulmonary absorption at a pH near the pKa. The results suggested that structurally related xanthones are absorbed possibly by passive diffusion across the lipoidal region of the pulmonary membranes and that the absorption of organic acids and organic electrolytes is mainly controlled by the lipid solubility of the unionized species.

Bicarbonate secretion in rat ileum and its dependence on intraluminal chloride.

ARTICLESBicarbonate secretion in rat ileum and its dependence on intraluminal chlorideKA HubelKA HubelPublished Online:01 Dec 1967https://doi.org/10.1152/ajplegacy.1967.213.6.1409MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByFundamentals of Epithelial Cl− Transport27 November 2020Slc26 Family of Anion Transporters in the Gastrointestinal Tract: Expression, Function, Regulation, and Role in Disease15 March 2019Fundamentals of Epithelial Cl− Transport15 December 2015Electrolyte Secretion and Absorption in the Small Intestine and Colon27 November 2015Electrogenic Cl− secretion does not occur in the ileum of the Australian common brushtail possum, Trichosurus vulpecula, due to low levels of expression of the NaK2Cl cotransporter, NKCC130 June 2009 | Journal of Comparative Physiology B, Vol. 179, No. 8A functional CFTR protein is required for mouse intestinal cAMP-, cGMP- and Ca 2+ -dependent HCO 3− secretion30 September 2004 | The Journal of Physiology, Vol. 505, No. 2The Pathophysiology of DiarrheaBicarbonate secretion in rabbit ileum: Electrogenicity, ion dependence, and effects of cyclic nucleotidesGastroenterology, Vol. 105, No. 6Comparative Physiology of Colonic Electrolyte Transport1 January 2011Ion Transport Across Mammalian Small Intestine1 January 2011On the mechanisms of the basal alkaline secretion in the rat ileum in vivoActa Physiologica Scandinavica, Vol. 142, No. 2Absorption and metabolism of procaine by the rat small intestineNaunyn-Schmiedeberg's Archives of Pharmacology, Vol. 342, No. 2Diarrhoea of famine and malnutrition--investigations using a rat model. 2--Ileal hypersecretion induced by starvation.Gut, Vol. 31, No. 2Studies of cholera toxin-induced changes of alkaline secretion and transepithelial potential difference in the rat intestine in vivoActa Physiologica Scandinavica, Vol. 138, No. 1Ion and Water Transport in the IntestineBiochemical and cytochemical comparison of intestinal bicarbonate-stimulated Mg2+ dependent ATPase and alkaline phosphatase activities in rat, rabbit and guinea pigThe Histochemical Journal, Vol. 19, No. 1Occurrence, absorption and metabolism of short chain fatty acids in the digestive tract of mammalsComparative Biochemistry and Physiology Part B: Comparative Biochemistry, Vol. 86, No. 3Pathogenesis and pharmacology of diarrheaVeterinary Research Communications, Vol. 10, No. 1Ion and Water Transport in the IntestineA comparative study of bicarbonate secretion by ileum and colon of Oryctolagus cuniculus. Influence of caecal pHComparative Biochemistry and Physiology Part A: Physiology, Vol. 79, No. 4Intestinal HCO 3 − secretion inAmphiuma: Stimulation by mucosal Cl− and serosal Na+The Journal of Membrane Biology, Vol. 68, No. 1Congenital Chloride DiarrheaBicarbonate-dependent chloride absorption in small intestine: Ion fluxes and intracellular chloride activitiesThe Journal of Membrane Biology, Vol. 53, No. 2THE INTESTINE AS AN ENVIRONMENT FOR HYMENOLEPIS DIMINUTAEffect of organic acid absorption on bicarbonate transport in rat colonPfl�gers Archiv European Journal of Physiology, Vol. 379, No. 1Permeability changes in the parasitized (Hymenolepis diminuta: Cestoda) rat intestineComparative Biochemistry and Physiology Part A: Physiology, Vol. 57, No. 2Deviations from the flux ratio equation for chloride ions in ouabain- and acetazolamide-treated frog skinBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 419, No. 3Hymenolepis diminuta: Acidification and bicarbonate absorption in the rat intestineExperimental Parasitology, Vol. 37, No. 1In Vivo Effects of Clostridium perfringens Enteropathogenic Factors on the Rat IleumInfection and Immunity, Vol. 10, No. 5Transport of Short Chain Fatty AcidsSalts and WaterSodium and Chloride Transport across Isolated Rabbit IIeumIntestinal chloride and bicarbonate transport in normal and enterectomized ratsJournal of Surgical Research, Vol. 14, No. 4Studies on the effects of unconjugated dihydroxy bile salts on rat small intestinal function in vivoBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 288, No. 2CARBONIC ANHYDRASE:ISOENZYMES. PROPERTIES. DISTRIBUTION. AND FUNCTIONAL SIGNIFICANCEBiological Reviews, Vol. 47, No. 4The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides in the small intestine of the rat in vivoGut, Vol. 13, No. 8An Overview of Intestinal Absorptive and Secretory ProcessesGastroenterology, Vol. 63, No. 1Effect of luminal pH on the absorption of water, Na+ and Cl− by rat intestine in vivoBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 233, No. 3Effect of luminal pH on the absorption of water, Na+ and Cl− by rat intestine in vivoBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 223, No. 3Experimental DiarrheaGastroenterology, Vol. 60, No. 6Besonderheiten der Sorption im Intestinaltrakt des MeerschweinchensPfl�gers Archiv European Journal of Physiology, Vol. 321, No. 3The role of the intestine in salinity adaptation of the rainbow trout, Salmo gairdneriComparative Biochemistry and Physiology, Vol. 30, No. 3Conservation of Sodium, Chloride, and Water by the Human ColonGastroenterology, Vol. 56, No. 1Carbonic Anhydrase Activity of Mucosa of Small Intestine and ColonNature, Vol. 219, No. 5150 More from this issue > Volume 213Issue 6December 1967Pages 1409-1413 Copyright & PermissionsCopyright © 1967 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1967.213.6.1409PubMed6075742History Published online 1 December 1967 Published in print 1 December 1967 Metrics

Absorption of Organic Acids from the Omasum ,

Summary Absorption of volatile fatty acids (VFA) and lactic acid from the omasum of 4- or 5- mo.-old Holstein calves was studied by two methods. The first consisted of a study of the relative concentrations of these acids in the contents of the stomach compartments of six calves in relation to concentrations of chromic oxide remaining from previous oral adininistration. On a dry matter basis, levels of chromic oxide increased in order from the rumen, to the reticulum, to the omasum, to the abomasum; and, in the same order, VFA declined. The ratios of VFA to chromic oxide indicated a decrease in VFA of 51% from the reticulum to the omasum and a further decrease of 83% from the omasum to the abomasum. The second method involved injection of sodium-n-butyrate-1-C 14 into the exteriorized omasum of two calves. Organic acid levels and distribution of C 14 activity were determined on samples of blood drawn simultaneously from the omasal vein and the carotid artery at various time intervals during 1 hr. following injection. The animals then were sacrificed and concentrations of acids and distribution of label in the ingesta of the stomaeh compartments were studied. Butyrate-C 14 was absorbed rapidly from the omasum into the blood of the omasal vein, peak concentrations appearing at 5 to 10min. after injection. Labeled metabolite continued to be absorbed throughout the experiment. Conversion of butyrate to other VFA occurred in the omasum, as indicated by the presence of label in the acids isolated from ingesta in that organ. The appearance of 50% of the recovered label in omasal blood in the form of lactic acid suggests an unknown pathway for the conversion of butyrate to lactate by omasal epithelium. Average concentrations of butyric, propionic, and acetic acids were greater in the omasal vein blood than in the carotid artery blood; the reverse was true for lactic acid. It is concluded that absorption of organic acids does occur from the omasum and apparently in considerable magnitude.

Influence of Ammonium Phosphate Buffers on Foliar Absorption of Organic Acids

1. The influence of ammonium phosphate buffers on penetration of 2,4-dichlorophenoxyacetic acid (2,4-D), a-naphthaleneacetic acid (NAA), and 3,6-endoxohexahydrophthalic acid (Endothal) into young bean leaf tissue was studied by measuring internode growth following treatment. 2. Uptake of these biologically active acids was found to be completely independent of their state of dissociation. The plant responses appeared to be mediated instead by the buffer anions. 3. H2PO- 4 enhanced uptake, while HPO-- 4 inhibited it. This ion antagonism resulted in growth inhibition which was proportional in magnitude to the concentration differential of the ion present in excess. This relationship produced empirical correlations between percentage internode repression and curves of buffer capacity.

Production and absorption of organic acids by the perfused goat rumen.

Summary1) Any inferences drawn from data of perfusion experiments must obviously be tempered by artificial conditions under which the tissue is operating. While recognizing that there are limitations it seems that a picture of the overall metabolism of the rumen may be formulated. 2) Large quantities of organic acids are normally produced in the rumen. On a diet of hay and grain relative rates of production of the VFA are in the order acetate > propionate > butyrate > valerate. Lactate may also be produced. Calculations based on data from perfusion experiments indicates that the organic acids are capable of providing up to 53% of the estimated net energy requirements of the animal. 3) Inter-conversion of organic acids may occur in the rumen. Butyrate in the rumen was converted to appreciable amounts of acetate and propionate and to lesser amounts of valerate and lactate. The interconversion of propionate in the rumen was negligible. 4) Acids produced in the rumen are absorbed as such into the blood of the...

The nature of the nerve receptor for the acid taste as indicated by the absorption of organic acids by fats and proteins

Distribution coefficients of thirteen organic acids between olive oil and water have been measured. The concentration in the water phase was about.02N. The acids were chosen so as to bring out the influence of certain polar groups, OH, CO, SO3H, NH2 and C=C. The effects of these groups are clearly marked, and are in general in the same direction and of the same order of magnitude as their effects on the concentration gradients of the same undissociated acids between water and the nerve receptor in the taste experiments ofTaylor, Farthing andBerman. Specific effects are noted for the NH2 and the phenyl groups.