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PARTITION AND ABSORPTION OF VOLATILE FATTY ACIDS IN THE ALIMENTARY CANAL OF THE RAT C. Remesy, C. Demigne To cite this version: C. Remesy, C. Demigne. PARTITION AND ABSORPTION OF VOLATILE FATTY ACIDS IN THE ALIMENTARY CANAL OF THE RAT. Annales de Recherches Vétérinaires, INRA Editions, 1976, 7 (1), pp.39-55. <hal-00900868> HAL Id: hal-00900868 https://hal.archives-ouvertes.fr/hal-00900868 Submitted on 1 Jan 1976 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. PARTITION AND ABSORPTION OF VOLATILE FATTY ACIDS IN THE ALIMENTARY CANAL OF THE RAT C. REMESY C. DEMIGNE Station de Physiopathologie de la Nutrition, Centre de Recherches de Clermont-Fevvand, I. N. R. A., Theix, Saint Genès Champanelle, 63110 Beaumont RÉSUMÉ RÉPARTITION ET ABSORPTION DES ACIDES GRAS VOLATILS DANS LE TUBE DIGESTIF DU RAT La répartition des acides gras volatils (AGV) dans le tube digestif et leur absorption ont été étudiés chez des rats recevant un régime comportant un mélange de céréales et de tourteaux de soja. Les concentrations en acide acétique et en acide D ou L lactique ont été comparées entre les deux zones de l’estomac du Rat : zone sécrétoire et zone non sécrétoire (cul-de-sac). Les concentrations les plus élevées de ces deux acides ont été trouvées dans le cul-de-sac, où le pH est le ,o). Les concentrations en AGV dans les contenus de l’intestin grêle ainsi que leur 5 plus élevé ( absorption sont négligeables. Des concentrations élevées en AGV ont été trouvées dans les contenus cacaux (environ 0 mM), alors que les concentrations en acide lactique sont très faibles. Le volume caecal et les 6 1 concentrations en AGV varient peu durant le nycthémère mais diminuent rapidement au cours des premières z 4 h de jeûne Dans le côlon proximal, les concentrations en AGV sont inférieures à celles du cxcum, en particulier pour l’acide butyrique. La caecumectomie provoque une diminution considérable des concentrations en AGV dans le côlon. La mesure des différences artérioveineuses au niveau de la veine caecale et de la veine du côlon a permis d’évaluer l’absorption des différents AGV ainsi que la cétogenèse. Il existe une corrélation étroite entre les concentrations en AGV des contenus cxcaux et les différences artérioveineuses. Chez le Rat, la cétogenèse au niveau de la paroi caecale est faible ( 12 p. 100 de l’acide butyrique absorbé) et nulle au niveau du côlon. Les AGV sont entièrement absorbés sous forme ionisée, lorsque le pH atteint !,5 chez les rats à jeun. Des mécanismes particuliers au caecum doivent être envisagés, peut-être en corrélation avec l’importante absorption de sodium à ceniveau. - ,, ,,, , _-,, . Volatile fatty acids (VI~A), produced mainly from fermentation of carbohydrates in the ration, constitute an important source of energy for ruminants. However, the role of the microflora in the digestion of carbohydrates and the production of VFA have not been extensively studied in monogastrics animals. The utilization of carbohydrates in the production of VFA by the microflora of non-ruminants implies that they reach the caecum in measurable quantities. This is not the case for simple sugars (fructose, glucose) which are completely absorbed in the small intestine. However, even with very digestible diets, some food particles have a very rapid transit and may reach the caecum without having been entirely hydrolysed or absorbed, as result of gastric discharge and intestinal peristalsis. This can only occur if the diet is not entirely soluble. In adults rats, certain disaccharides such as lactose are not hydrolysed completely in the small intestine for the lactase activity falls abruptly in weanling rats HT ). In the absence W (I, , R E c 1973 of enzymatic digestion it is evident that celluloses and membrane sugars also will reach the caecum. Sugars of endogenous origin can also constitute substrates for bacterial metabolism. Indeed in germ free rats, the caecum contains considerable amounts of T, G D STF IND STAFSON, ig&!). U carbohydrates INS (L T D TE , I, In addition to carbohydrates fraction, the microbial flora can utilize proteic nitrogen for its own synthesis (after hydrolysis and deamination) or also as an energy This bacterial metabolism results in the production of various compounds VFA from various substrates. ANOH and MICI!LS>;N M N R YANG, A 1970 demonstrated the production of ( ) VFA in the rat caecum although this rodent is not a strict herbivore. In the rat the development of the caecum, and consequently that of the flora, varies according to the diet and is thus to a certain extent controlable. Since a measurable flora is present in almost the whole length of the alimentary canal, studies were made of the VFA production in the stomach, small intestine, caecum and colon. Absorption of VFA by the caecum wall in rat has been show by YANG, MnNOxAxArr and OTTAZ and E MICI!>;I,S!N ORB (ig W 1970 M ( ), 2). We determined the extent of this 7 absorption in each part of the alimentary canal by arteriovenous differences in VFA concentration compared with the VFA levels in the digestive contents of each region studied. Ketone body production was also studied by arteriovenous differences in the caecum and the colon walls. This paper describes a part of a thesis work SY 1973 E M (RE , ) in which a great number of animals was used. source. such as EXPERIMENTAL Animals and diets All the experiments were carried out with Sherman rats fed to appetite, the dark period was from 20 00 h to 8. . 00 h. The diet was commercial pellets from Sanders ( iz6o Juvisy-sur-Orge, 9 France) comprising (parts of weight) : wheat 31 , maize 31 , soya-bean meal ( 50 p. 100 protein) 8, molasses 5 2 , salts and vitamins 5 . The overall composition of this diet was : 20 p. 100 crude protein, 2 p. 100 lipid, 4.! p. 100 crude fiber, 7 p. 100 minerals and vitamins and y p. too water. Germ-free rats were from C.N.R.S. Laboratories, 9 o Gif-sur-Yvette (France) (Courtesy m of Dr Snc!uEr). Physiological techniques Cectomy. n l aecu The rats are anaesthetized with ether. After laparotomy on the white line the caecum was exteriorized and the attachments of the appendix to the ileum were cut. A sterile cord was knotted above the ileocaecal valve, the caecum was cut and the caecal walls remaining were carefully cleaned with sterile saline solution. The ligature stops loss of blood and its impermeability made a gathered-suture unnecessary. Conjunctive attachments then formed at the level of the cicatrice without affecting the functionning of the ileocaecal valve. The operation lasted 3 to 4 minutes and losses from a break in passage are very low (less than 10 p. 100 ). Recuperation was very rapid. The following symptoms resulted from caecumectomy : hypertrophy of the colon, light diarrhea and slowed growth. Blood This sampling. carried out on animals anaesthetized with ether. After median laparotomy the ves6 mm). The portal blood was collected punctured directly using a needle ( 5 X 1 . 0 just above the branching of the portal vein, where it enters the liver. Blood from the stomach was removed from a length of the gastric vein after separating the spleen from the stomach. The blood draining the caecum was sampled as high as possible before the confluence with the blood from the ileum and that draining the colon at the limit of the ascending colon. To sample the blood irrigating the ileum or the colon, the caecal vein had first to be ligatured, in order to eliminate mixture due to blood coming from the caecum by way of anastomoses. sels was were <Sampling of digestive contents. Samples of approximately I g fresh weight from the various parts of were placed in Eppendorf microtubes and immediately frozen at C. 0 20 the alimentary canal - Biochemical techniques Plasma V FA. VFA are extracted from plasma with ethanol in the presence of a known quantity of internal standard (isobutyric acid). After addition of NaOH and evaporation of the ethanolic solution of the sodium salts, the residue is dissolved in a dilute solution of orthophosphoric acid to permit MIGNE, 1974 E analyses by gas liquid chromatography (REMESY and D ). Plasma ketone bodies. -hydroxybutyric and acetoacetic acids were measured in plasma using an enzymatic 3 DLA_VBY and KREBS, 19 L method (!’ILLIAMSOLB, ME 62). VFA the digestive contents. To test whether a single centrifugation was sufficient to extract the VFA from the precipitate, a comparison was made of the results after distillation and after centrifugation of a mixture from of caecal contents. Steam distillation. As for measurement of plasma VFA, isobutyrate was chosen as internal standard since there are only traces in the caecal content. Distillation was by the following 5 p. 100 5 ml 8 . procedure : I g of fresh material was diluted in 20 ml of water, acidified with 0 (w/v) 4 P0 and I ml 40 mM/1 of Na isobutyrate was also added before distillation. One hunS H dred and fifty ml of distillate were collected in a beaker containing excess sodium hydroxide. The distillate was evaporated and redissolved in 2 ml of water and o.I ml I o p. 100 (w/v) H 4 o p 3 before gas chromatography. of the digestive contents were centrifuged in Eppendorf microtubes Centrifugation. after storage at C to obtain the maximum volume of supernatant. To one volume of super0 20 1 volume of 10 p. 100 (w/v) H,P0 . natant ( 4 50 !,1), I volume of 40 mM internal standard and 0 were added. If the results obtained by distillation are expressed as a function of the caecal water (!!-8o p. 100 of the fresh weight), similar concentrations and percentages are obtained in both cases. The analyses of the digestive contents were therefore made using centrifugation. Samples - Lactic acid from the digestive contents. D and L lactic acid from the digestive contents were measured after centrifugation and dilution of the supernatant ( 40 4 M ( . 19 v). The enzymatic determination was made I v) in -’C’0 with L-lactate dehydrogenase (EC 1 . 27 8) from 2 . ) or D-lactate dehydrogenase (EC 1 OHORST procedure 6 H S 19 but with a diluted buffer ( ( ) 5 25 M glycine, . 0 Boehringer, according to ’ 20 M hydrazine and 0. . 0 03 M S CO 2 K ’ ) RESULTS Stomaclc and small intestine contents Sto!nach. samples were taken in the morning after separation of the complete gastric parts : one from the translucent zone (non secretory region) and the other from the opaque zone (secretory region). The VFA in these two parts of the stomach were analysed (see table z). There were significant differences (P < o.ooi) between the two zones for acetic acid 6.o mM compared with 13 (translucent zone 5 9 mM in the opaque zone) and for pH . .o and 3 5 ( .6). Only traces of the other VFA (propionic and butyric acids) were present. The difference between the dry matter percentage measured in the two regions 4 p. 100 and opaque zone 3 . i.o p. 100 (translucent zone 45 ) was not sufficient to be of any importance. The lactic acid in two parts of the gastric content was measured. The concentration was 141 1 mM in non secretory region (6 . 5 p. 100 of I,-isomer) and 4 mM in the 100 of secretory region (55 p. 8. 3 I,-isomer). Thus the same gradient The contents into two occured as for VFA but the concentration of lactic acid was greater. Small intestine. Only small quantities of acetic acid were found in the duodenum ( 5 mM) . 1 and only traces in the jejunum. Although concentrations of this acid were higher in the ileum they remain relatively low (6. 1 mM) (table z). Caecum contents The VFA concentrations were practically uniform in the entire caecal contents the values obtained in the appendix and near the ileo-caecal valve indicate. The lactic acid concentrations were always very low ( < 5 mM) in contrast to those in the gastric contents (table 2 ). as Caecal development. The caecum of young rats developed very rapidly after weaning and its relative weight reached a maximum in I oo g rats ( 7 p. 100 of body weight against . 2 . p. 100 for 100 g rats and i. 2 o g rats). The differences between 100 g 9 p. ioo for 33 rats and 330 g rats were not significant. Diurnal variations. Diurnal variations in the relative weight of the caecum were negligible. For in 1 0 g rats the variation was from 2 6 00 h to 2 . . p. 100 at 4 p. 100 at 10 . i8.oo h. Between the groups of rats used during the year VFA concentration remained very stable, particularly in the morning, but a certain variation may be noted in the evening when the animals began to go hungry (table 3 ). example, Fasted animals. The animals were deprived of food in the morning and killed after 24 or 4 8 hours. A considerable fall in VFA concentrations resulted during the first 24 hours (more than 6 0 p. ioo). Thereafter, as the starvation was prolonged, the VFA concentrations tended to diminish more slowly. In addition the percentage of butyric acid diminished noticeably, from 15 to 10 p. 100 . The decrease of VFA concentration 1 after . 1 and 7.6 ! 0 . gives rise to an increased pH of the caecal contents : 7..! ! 0 24 or 4 8 hours (table q.). Germ-free In aszimals. rats we determined that there traces of acetic acid (table 4 ). germ-free ting only Colon content was no VFA in the caecum excep- and faeces Animals fed and fasted. The concentrations of VFA in the contents of the first part of the colon was of the caecum in the same animals. During the passage of the . 4 mM. contents in the colon, the VFA level decreased from, for example, 1 4 to 112 7 8 This was particularly clear for butyric acid, the percentage of which decreases from 14 2 p. 100 . . This phenomenon was also found after fasting (total VFA : 1 to 10 . caecum 4 o.imM for a 4 51 , and colon 3 8 hours fast) (table 5 ). These differences cannot be explained by variations in the levels of dry matter, which were very similar in the caecum and the proximal colon. compared with those Caeciimectom , 3 . Samples were taken from the colon and the ileum (and also in the caecum of controls) 21 days after the caecumectomy. The reduction of VFA levels in the colon was considerable and the proportions of propionic and butyric acids were low and unstable whereas in the ileum the VFA concentrations were always very low (table 6). Faeces. VFA concentrations, expressed per gram of dry matter, are about 75 p. 100 of those found in the colon content: the proportion of each acid were similar to those of caecum and colon contents (table 2 ). A bso j5tion y bil di!’erent Parts of the alimentary canal Stomach aaad small intestine. The low concentrations of acetic acid (6. 2 mM) observed in the pyloric region shows that VFA absorption is very active in the stomach. Difference between gastric vein blood and arterial blood is 0 35 mM for acetic acid. Propionic acid and . acid were when noticeable butyric present only quantities of these acids were measured in the gastric contents. The absorption of VFA in the small intestine appeared negligible (ileal vein o.i 3 and artery 0 15 mM) to the point that it may be masked . by metabolism of the walls. Caecum and colon. In rats VFA absorption occured to a considerable extent and colon. The arteriovenous differences for these two organs only were in the caecum determined in with the concentration of the digestive contents. The arteriovenous differences were proportional (r > 8) 97 to the respective concentrations of VFA . 0 in the caecal contents (fig. i). This good correlation indicates that the blood flow is proportional to the caecal volume. As in the caecum, there was considerable VFA absorption particularly of butyric acid by the wall of the colon (table 7 ). comparison Ketogenesis b v the caecum and colon walls. Since the caecal contents contained no ketone bodies the arteriovenous diffefound for D-hydroxybutyrate and acetoacetate resulted from meta3 bolism of VFA (especially butyrate) by the caecal wall. The quantities of acetorences and 3 -hydroxybutyrate produced were quite similar. Together they represented 12 p. 100 of the butyric acid absorbed at the level of the caecum (table !). Total absorption acetate Diurnal variations and influence of fasting. proportions of VFA were absorbed by the portal and caecal veins, the indicating important role of the caecum. The greatest reduction in absorption occured during the first 24 hours of starThe same vation, thereafter, it occured more slowly. The portal arteriovenous differences varied with the concentration of VFA in the caecum contents : the absorption of butyric acid was particularly reduced (table 8 and fig. i). The arterial levels of acetic acid was nous modified very little, which indicates that acetic acid origin (A!rmsorr and WHITE, i962). Influence of caecumectomy. This operation permitted can be equally of endoge- estimation of the part due to the caecum in the vein. Caecal ablation was very rapid and it was absorption by portal to after one take about minute, as for the controls. The acetic acid possible samples levels in the portal vein dropped from 0 21 mM and those of butyric acid . 51 to 0 . mnI in the became difficult to Since it was absent from artedetect. 8 . 0 ( controls) rial blood and little metabolised by the caecum wall, propionic acid in portal blood permitted a correct estimation of the absorption by the caecum : o.2r mM in the control, but reduced to 0 07 mM in operated animals. Thus, it can be estimated . that the caecum absorbed 2/3 of the VFA. When rats had been caecumectomized for 2 i days, absorption was much reduced and did not equal that of the colon in normal animals since fermentations in the colon were depressed in animals which had undergone a caecumectomy (table 6). total an the DISCUSSION Stomach In the rat, the presence of an important non secretory region with an wall is extremely favorable for the development of fermentations and the content of the cul-de-sac has a longer transit time. epithelial probably In the stomach, lactic acid is found in greater quantity than acetic acid : mM of acetic acid compared with 141 1 of lactic acid. The development of a . microflora in the stomach may depend on the heterogeneity of the gastric contents as confirmed by pH levels, which were sufficiently high to permit development of an acidophile flora. The fermentations were no doubt greatest in certain small parts of the stomach and were facilitated by the presence of complex coarsely ground rations. The concentrations of both acetic and lactic acids were much greater in the cul-de-sac zone than in the secretory zone. In the rabbit, H ENNING and IRD ( H 1972 a) showed diurnal differences in the division of acetic acid between he fundic and cardiac zones. The extent of coprophagy in our animals was not determined but BARN!s et al. ) . It is possible 1957 estimated that it could reach 50 p. 100 ( that extensive coprophagy may increase fermentation for the ingested faeces provide a source of VFA, of substrates and of microbes. The reingested faeces, found mainly in the cul-de-sac, did not become homogenised with the gastric contents immediately. They can therefore, constitute fermentation centres in which the pH, substrates and microorganisms differed from those of the gastric liquid. 6.o 5 Small intestine In the small intestine, the sudden increase in pH caused by the pancreatic and intestinal secretions and the antiseptic effect of the bile salts stopped the acidophilic fermentations. SMITH and T AYLOR (i j8) discovered that VFA could be transported 9 across the duodenum mucosa of the rat even against a concentration gradient. The extent of this transport was probably not very great since VFA production in situ was negligible. There was no significant increase in acetic acid in the ileal vein ( 13 mM in the vein, compared with o.1 mM in the artery) which indicates . 0 that the small amount of acetic acid absorbed is completely metabolised by the intestinal wall. Caecum Types of fermentations. The large volume of the caecum and its remarkable constancy of weight for a given diet show that transit is efficiently regulated in this part of the alimentary canal. The stable conditions in this organ are very favorable for the development of a flora adapted to the substrates coming from the small.intestine. As a result, VFA concentrations tended to remain rather constant throughout the day and over long periods when the animals were kept in stable conditions. These observations suggest that mechanisms may exist which regulate the still little studied caecal production of VFA in monogastrics. It is not impossible that high concentrations of VFA are capable of inhibiting bacterial metabolism. In addition, interactions between different types of bacteria (fusiform and coliform bacilli) may be induced by the VFA (LEE and GE , 2). L E MM ETE (F 97 However this is a point of some controversy R i and AB AMS, I9!2). R Germ-free animals show a considerable increase in caecal volume accompanied by atrophy of mucosa and musculosa (AsArto, 19 ). The role of VFA, known 9 6 to have an effect on the morphogenesis of rumen epithelium (SANDER et al., 1959 ), have not been yet studied. It is of interest to note that the constancy of the caecal volume and caecal VFA concentration may permit a rapid estimation of the extent of bacterial digestion with a given diet. A similar relationship has been demonstrated between production of VFA in the rumen and either concentration (L RETT 19 B ENG and , 66) or pool size estimated by concentration of VFA and rumen volume (W ESTON and HoGAN, The concentrations found in in contents of rats on the caecal the the g68). I morning described diet (acetic acid : 90 mM and butyacid I20 mM ; propionic 50 40 ric acid : 20 from and those A M NOHARAN YANG, o mM)differ 3 reported by who found a of acid than of MrcK!t,s!v ) butyric greater proportion 1970 ( propionic acid. Lower concentrations are often found in the rumen and the caecum of ruminants (P ACKSON 19 J TT, MY!RS and , ACKE 66) and proportions of V FA vary simiRAS and KA F R , 19 Y larly in the caecum and in the rumen (O ). 9 6 ,E RSKOV Metabolism of VFA by the walls of the alimentary canal. 1972 b, c) showed in vivo with ( IRD ENN and H H G N i rabbit that the caecal wall transforms only a small fraction of radioactive butyrate into ketone bodies (about ORBE 13 p. I oo). These workers found greater ketogenesis in vitro, and similarly W TAZ ) T O and M 1970 noted considerable ketogenesis from butyric acid in rat in vitro. ( Our results obtained by arteriovenous differences after a short anaesthesia ( 2 mn) in the same conditions as for the VFA show that there was little ketogenesis in the caecal wall. Transformation of 12 p. I oo of butyric acid gives almost the totality of the ketone bodies produced. Although high concentrations of VFA exist in the colon content we found that there was no ketogenesis by the walls. These results IRD ( NNING and H agree with those of HE 1972 c) in the rabbit, which indicated that the reduction in activities of enzymes of ketogenesis in the colon is correlated with the distance from the caecum. However, it is probable that in rats this reduction is more marked. In contrast with ketogenesis, G IRD ( ENNIN and H H 1972 b) found that there was no regular reduction in the oxydation of butyrate to CO, along the colon and it was not correlated with the concentration of VFA in the lumen. Absorption. The arteriovenous differences do not give quantitative measurements of the absorption of different acids since the rate of blood flow and the extent of metabolism in the wall were not known. The close parallel between VFA concentrations in the caecal contents and the arteriovenous differences in rats shows that absorption occurs in the direction of the concentration gradient and is not affected by metabolic inhibitors , RS JeCKSOIV and PACK!TT, Ig6!). Classic results (DANIE E Y (M , 1945) LLI showed that the free forms of VFA traverse lipoproteic membranes of rumen epithelium more easily than the dissociated forms. The decrease of pH probably increases VFA absorption, at least in the rumen (AAFJES, 7 g. I ) 6 However in the caecum the VFA are always absorbed, although they are entirely in ionized form (pH about 7 ), in fasting animals for instance. In 5 . addition, a pH increase does not cause any modification of the proportion of the VFA absorbed, these proportions are the same as in the caecal contents. No completely satisfactory mechanism for VFA transport in the caecum of rats has been described. The most precise investigations concern jejunal absorption in the rat (SMITH and TAYLOR, 1958 ; Jecxsorr, 1974). Some observations suggest involvement of sodium transport in absorption of VFA in ionized form, as this sodium transport in R R A Z IO, E MiLLER, ENGEI,particularly important in the hind-gut (F,DMONDS, ig7q ; N A75). H 9 1 RDT, No clear differences exist between the absorption of acetic, propionic and butyric acids could be observed. ETT, RS J E Y M ACK , P ACKSON 66) 19 showed that in sheep ( acetic acid was more utilised by the caecal wall than was propionic acid. In the rat, acetic acid metabolism by the caecal wall is probably small in absolute values ; the metabolism of 12 p. 100 of the butyric acid to ketone bodies shows that it penetrates the caecal wall most rapidly (if we assume the ketogenesis is only from buty- rate). The concentrations found in the caecal vein represent about 2 p. 100 of those in the caecal contents although M OTTAZ and Woxsx ) 1972 cited figures of about ( from in . 100 This could result differences the rate of blood flow during 4 p. divergence the sampling. The same parallel between the concentrations in the caecum and in IRD ( the caecal vein was observed by H ENNING and H 1972 c) in the rabbit. In the colon in the absence of ketogenesis butyric acid is still absorbed the most rapidly and acetic the most slowly. This suggest that the mechanisms of absorption are different in the caecum and the colon. The influence of fasting. The reductions in concentration which we measured are significant only if the reduction in caecal volume is taken into account. YANG, M ANOHARAN and MiCKELSEN 1970 found that during fasting the reduction in the quantity of VFA present in ( ) the caecum could be described by exponential functions. The presence of residual amounts of VFA in the caecum of animals subjected to a prolonged starvation poses the problem of the origin of the substrates used for these fermentations. They may arise from degradation of endogenous mucoproteins, passage of various molecules from the blood into the alimentary canal and also recycling of various substrates after coprophagy. As in those fed normally, in fasted rats the relativeabsorption of the VFA depends on the concentration within very wide limits, despite an increase of the pH. Colon Caecumectomy, in spite of a dilation of the colon and slowing of the transit, resulted in very low levels of VFA in this organ. Modifications of colic fermentations suggest that caecum VFA have effects on the nature of the colon flora. In addition, there may be considerable lysis of bacteria in the Rat’s colon as in Rabbit’s, which may be due to a lytic compound (B ONNAFOUS and RAy!rAUn, 19 68). Im!oytayace of VFA as an energy source. The VFA appear to provide a regular source of energy which reduces the sudden fluctuations in the supply of nutrients after feeds. In addition the nutrient source is equilibriated since VFA provide both glucogenic and lipogenic precursors. It is difficult to establish exact balance accounts since the rate of flow and fluctuations of the portal vein were not determined. VFA concentrations in the portal vein is far from negligible in rats compared in similar conditions with ruminants : I to 3 mM of acetic acid in ruminants compared with 0 .8 mM in rats (A 5 to 0 . SON, HILL and NNI I,!WIS, 1957 ; BENSADOU DINE and RF A L PA , S N , ig6z ; CooK and MILLER, 1965). ID Comparison of these figures must take into account possible difference in the metabolism of acetic acid by the rumen and caecum walls. R and E A H O N ISEN M L CK ) YANG, MA .7 p. ioo the contri1970 estimated at 4 ( bution of VFA to the digested energy in the rat with a diet comprising mainly ground maize and soya-bean meal : in this diet certain carbohydrates of soya-bean are probably the main substrates for caecal fermentations. The importance of VFA AN S OEST and YOUNG 6 depends on the diet since KEYS, V 19 found that lucerne ( ) 9 hemicellulose could have greater than 40 p. ioo digestibility when this species made 0 p. 100 of the diet. The energetic importance of VFA is much greater in rumiup 5 nant (ANNISO!r and , RMSTRONG 1970 A ) but the extent of caecal fermentations are certainly comparable for rat and ruminant in which the fermentative capacities are limited Tlac role RSKOV (0 et al., ig7o). of fermentation. In rats the development of fermentations appears to be linked with the presence of easily fermented carbohydrates as the period of transit is relatively short. The action of the flora increases the energy available to the animal since the poorly digestible carbohydrates are transformed into VFA. These VFA are almost completely absorbed in the colon and faecal looses are small. In addition, the presence in the caecum of highly fermentable substrates such as starch results in increased faecal loss of nitrogen of bacterial origin in both rat and sheep (MASON and E SKOV et al., zg ALM ig P , R 73 ; 0R o). The origin of the nitro7 gen incorporated into bacterial cells has not been determined. It is possible that part of the excretion of urea occurs in the caecum, reducing the extent of urinary excretion of nitrogen. The exchanges between the pools of free amino acids in the plasma and in the caecal and colon contents are poorly understood. Since the concentration of free amino acids in the colon and the caecum is weak (CoMS! and PION, ig66), extensive exchanges between the plasma and digestive contents could occur only if there are mechanisms for active or facilitated transport. More complete balance sheets of caecal fermentation need to be established and the influence of quantity and type of substrate determined including that of poorly digestible proteins which escape enzymatic attack (membrane or tannined proteins, hexosamines). Requ pour publication en ddcembre 1975. SUMMARY The partition and absorption of volatile fatty acids (VFA) have been studied in the rat purified diet comprising mainly a mixture of cereals and soya-bean meal. . The concentration of acetic and lactic acid was compared in non secretory (cul-de-sac) 2 and secretory regions of the stomach. The greatest concentrations of both acids were found in the cul-de-sac region where the pH was highest (pH 5 ). 0 . . Concentration and absorption of VFA were negligible in the small intestine. 3 i. using a non High VFA concentrations were found in the caecal contents, while lactic acid concentrations were lower. The volume and concentrations of the caecum contents varied little during the 4 h of fasting. day and decreased rapidly during the first z The concentrations of VFA, particularly that of butyric acid, were lower in the proximal colon than in the caecum. Caecumectomy caused a considerable decrease in VFA concentra tions in the colon. 6. Arteriovenous differences in VFA and ketone bodies were studied for the caecal and colun veins in rat. A close parallel between VFA concentration in the caecal contents and the arteriovenous differences was observed. In rat, ketogenesis was weak in the caecal wall ( 12 p. 100 of butyric acid absorption) and negligible in the colon wall. VFA are absorbed entirely in ionized form when caecal pH attains 7 5 in fasted rats. Special mechanisms for caecal absorption should . therefore be considered, perhaps linked with the large sodium transport in the caecum. The relatively high VFA concentrations measured in the portal vein suggested that they are important in the digestive processes. REFERENCES The disappearance of volatile fatty acids through the amen wall. Z. 1-ierph!!siol. l’ierernâhr. Futtermittelkde. Dtsch., 22, 6 -75. 9 . Absorption ILL K. J., L EWIS D., 1957 lNV E. F., H : N aso . Studies on the portal blood of sheep. 2 of volatile fatty acids from the rumen of the sheep. l3iochem. J., 66, 592 . 99 -5 &dquo;HI R. R., 19 N B NNISON E. F., TE A . Further studies on entry rates of acetate and glucose in sheep, 2 6 with special reference to endogenous production of acetate. 13iochem. ,1., 84, 54 2. 55 6NNI A O S N E. RM F., A D. G., 1970 srRONG . VFA metabolism and energy supply, in Physiology of Digestion and Metabolism in the Ruminant p. 422 , Phillipsan A. T. Ed., Oriel Press. RGEN R. A., MiLLER Ii., anaDT A zio NÇEL W. V., 1975 E . Ion, water and volatile fatty acid absorption in the large intestine of the goat. i6‘th International Synaposium, Ruminant Physiology. Sidney AFJES J. H., 19 A . 7 6 (in press). T., y . 9 6 SANO A resin. Modification of cecal size in germ-free rats by longterm feeding on anion Chang Y e rr-g 9 B . J. Physiol., 217, I ar.w G., lVIcG c R. H., F· r B., n E Am. ROWN A., 1957 B . Prévention of coprophagy in the rat. J..Vutr., 63, 8. 49 9 8 4 ENSADOUN A., PnLAmNES O. L., REio ,J. T., 19 B . Effect of level of intake and phy·sical forin of 2 6 diet on plasma glucose concentation and volatile fatty acids absorption in ruminantx. J. Dairy Sci., I2IO I203 45, . BoNNnFOOS R., Rx nun P., 19 YN lon proximal sur p 68. Mise en évidence d’une activité lysante du c les micro-organismes du tube digestif du Lapin. Arch. Sci. Physiol., 22, 57 . 4 -6 COMBE E., PioN R., 19 66. Note sur la composition en acides aminés du contenu de caecums de rats 259 255 axéniques et de rats témoins. Ann. Riol. !4tMM!. Biosh, Biophys., 6, . CooK R. M., Mm:r. a L. D!; 19 E . Ütilization of volatile fatty acids in ruminants. Removal from portal 5 6 blood by the liver. J. Dairy Sci., 48, 6 13 1339 . 4 i N Dn r L ,i r J. F., CK ARSHALL R. A., N so A. T., 194 p i LL Pui ITCIICO M. W. S., M H 6. The mechanism of absorption from the rumen as exemp ified by the behaviour of acetic, propionic and butyric acids. l ,1. Exp. Biol., 22, 75-84. ns C. J., 19 N o m n ? 7 8, D. H. Smrrn Ed., 2 . Salts and water, in Rïomembranes, Intestinal absovption, p. 7 4 7 S NF I3nrz _ Plenum Press N. Y. and London. FRETER R., A BRAMS G. D., 1972 n of various intestinal bacteria in converting germ free mice p . Funeti to the normal state. Infection and Immunity, 6, 6. 12 19 I IRD F. J. R., 1972 a. Diurnal variations in the concentrations of VFA in the tlinienING S. J., H HENN tary tracts of wild rabbits. Br. y..V«<)’., 27, 57 . 4 -6 IRD F. J. R., 1972 b. Ketogenesis from butyrate and acetate by the cecum and the E H I N NG N S. J., H colon of rabbits. 33ioclaem ; J., 130, 90 -7 5 78 . rrrxr S. J.> Hr l I C N RD F, J. R., 1972 c. Transport of acetate and butyrate in the hind gut of rabbits. 91 7 l3iochem., J., 130, -796. Hoaoxs H..1., rg65. T N. Y. and London. Methods of enzymatic analysis p. acm B t V z Ed. Acad. Press. 66- H. V. E 2 . 277 M. J., i9!4. Transport of short chain fatty acids, in Biamernbranes, Intestinal absorption 6. 7 3 67 0 D. H. Smt!Tn Ed. Plénum. Press N. Y. and London. EY J. E., V K s AN S OEST P. J., Y OUNG E. P., 19 . Comparative study of the digestibility of forage 9 6 cellulose and hemicellulose in ruminants and non ruminants. J. Anim. Sci., 29, . I5 II CKSON JA p. L E E A., G EMMEL E., 1972 . Changes in the mouse intestinal microflora during weaning : role of volatile fatty acids. Infection and Immunity, 5, 1 . 7 EICH J., 3 L R TE ;utr., B g7 Effect of dietary lactose on intestinal lactase activity in young rats. J. 1 I . 39 392 103, 6. measurements of the rates of production of acetic, of different diets and the correlation between production rates and concentrations of these acids in the rumen. Br. J. Nutr., 20, 541-552. INDSTEDT G., r L INDSTED S., GusTAFFSO:v B. E., 19 L . Mucus in intestinal contents of germ free 5 6 rats. J. Exp. :’Vled., 121, . 214 201 ASSON V. C., PALMER R., 1973 M . The influence of bacterial activity in the alimentary canal of rats on caecal nitrogen excretion. Acta. Agric. Scand., 23, . 4 1 1 49 1 RBE J. F., 1972 Mornwz P., ii’o . Taux des acides gras volatils dans la veine caecale du Rat. Influence du contenu caecal. J. Physiol. Fr., 65, 275 A. ACKETT I. V., 19 rilrEas L. L., J ACKSON H. D., P . Absorption of volatile fatty acids from the 7 6 cecum of sheep. J. Anim. ,Sci., 26, 8. 145 1450 AV R. N., 19 RSKOV E. R., F 0 RASER C., K . Dietary factors influencing the digestion of starch in 9 6 the rumen and small and large intestine of early weaned lambs. Br. J. Nutr., 23, 6. 22 217 ASSON V. C., M ANN S. O., 1970 RASER C., ryl RSKOV E. R., F 0 . Influence of starch digestion in the large intestine of sheep on caecal fermentation, caecal microflora and faecal nitrogen excretion. Bv. G R. N E L RE D. J., 19 B H., T 66. Simultaneous propionic and butyric acids in the rumen of sheep -68 1 67 . J. Nutr., 24, 2 YERS L. L., JA P A CKETT L. V., M CKSON H. D., 19 66. Gastrointestinal content and mucosal oxidation of volatile fatty acids in sheep. J. Ani!xt. 5et., 25, 09 -4 2 0 4 . EMESY C., 1973 R . Contribution à l’étude de la production et du métabolisme des acides gras volatils chez le Rat. Thèse, Université de Clermont-Ferrand. EMI C., 4 D E N EMES C., G R igq Determination of volatile fatty acids in plasma after ethanolic extracI . tion. Biochem. J., 141, . 91 5 8 ANDER E.G.,W S ARNER R. G.; IIARRISON OOSLI H. N., L 1959 J. K., The stimulatory effect of sodium . butyrate and sodium propionate on the development of rumen mucosa in the young calf. J. Dairy . 0 6 1 0 5 Sci., 42, AYLOR C. B., 195 D. H., T 8. Intestinal transfer of short chain fatty acids in vitro. ,%. Physiol., 141, 0 -8 3 7 . ESTON R. H., Hocw:! J. P., 19 BV 68. The digestion of pasture plants by sheep. i. Ruminal production of volatile fatty acids by sheep offered diets of ryegrass and forage oats. Aust, J. A gric. Res., 19, 419 - MITH S . 2 43 D. I-L, M ELLANBY J., S EB H. A., 19 R K (―) fi-hydro’ . Enzymic determination of D 2 6 6. 9 xybutyric acid and acetoacetic acid in blood. Biochem. J., 82, goTTAZ P., 1970 ORBE J. F., VIo &dquo;’ . Métabolisme et absorption de l’acide butyrique par le caecum de 66, 5 6 rat. J. Physiol. Fr., 62, 4 ANOHARAN K., M ICKELSEN O., 1970 YANG M. G., NI . Nutritional contribution of volatile fatty acids from the cecum of rats. J. !V:(<<’., 100, 545 . 0 -55 !VILLIAmsoN