Dietary resistant starch and chronic inflammatory bowel diseases

These studies were performed to test the benefit of resistant starch on ulcerative colitis via prebiotic and butyrate effects. Butyrate, propionate, and acetate are produced in the colon of mammals as a result of microbial fermentation of resistant starch and other dietary fibers. Butyrate plays an important role in the colonic mucosal growth and epithelial proliferation. A reduction in the colonic butyrate level induces chronic mucosal atrophy. Short-chain fatty acid enemas increase mucosal generation, crypt length, and DNA content of the colonocytes. They also ameliorate symptoms of ulcerative colitis in human patients and rats injected with trinitrobenzene sulfonic acid (TNBS). Butyrate, and also to a lesser degree propionate, are substrates for the aerobic energy metabolism, and trophic factors of the colonocytes. Adverse butyrate effects occur in normal and neoplastic colonic cells. In normal cells, butyrate induces proliferation at the crypt base, while inhibiting proliferation at the crypt surface. In neoplastic cells, butyrate inhibits DNA synthesis and arrests cell growth in the G1 phase of the cell cycle. The improvement of the TNBS-induced colonic inflammation occurred earlier in the resistant starch (RS)-fed rats than in the RS-free group. This benefit coincided with activation of colonic epithelial cell proliferation and the subsequent restoration of apoptosis. The noncollagenous basement membrane protein laminin was regenerated initially in the RS-fed group, demonstrating what could be a considered lower damage to the intestinal barrier function. The calculation of intestinal short-chain fatty acid absorption confirmed this conclusion. The uptake of short-chain fatty acids in the colon is strongly inhibited in the RS-free group, but only slightly reduced in the animals fed with RS. Additionally, RS enhanced the growth of intestinal bacteria assumed to promote health. Further studies involving patients suffering from ulcerative colitis are necessary to determine the importance of RS in the therapy of a number of intestinal diseases and the maintenance of health. Accepted: 11 August 1999     

In vitro contractile effects of short chain fatty acids in the rat terminal ileum.

Short chain fatty acids (SCFAs), produced in the gut by bacterial fermentation of carbohydrates, change intestinal motility by mechanisms as yet unknown. This study examined the mechanism(s) of action of SCFAs on contractility using isolated rat terminal ileum segments and isolated ileal smooth muscle cells. Strip contractions were recorded under isometric conditions. Intracellular calcium concentration ([Ca2+]i) was measured in single cells loaded with indo-1 penta-acetoxymethyl ester (indo-1 AM). SCFAs (10(-9) to 10(-2) mol/l) induced concentration dependent contractions. The effect was not different among the individual SCFAs. Exogenous acids (namely tartaric and citric acids) caused similar responses as SCFAs, whereas sodium acetate had no effect. The contraction was not blocked by tetrodotoxin, atropine or hexamethonium, showing that it was not mediated through a cholinergic pathway. Moreover, removal of the mucosa or addition of procaine (a local anaesthetic) to the bath did not change the SCFA induced contraction, while verapamil (a calcium-channel antagonist) completely suppressed it. In addition, application of SCFAs to isolated ileal myocytes evoked peaks in [Ca2+]i inhibited by D 600 (a blocker of voltage dependent calcium channels). Taken together, these results suggest that the contractile response stimulated by SCFAs in the rat terminal ileum could result from an acid sensitive calcium dependent myogenic mechanism.     

The effects of short-chain fatty acids on colon epithelial proliferation and survival depend on the cellular phenotype

PURPOSE: The short-chain fatty acids (SCFA) are produced via anaerobic bacterial fermentation of dietary fiber within the colonic lumen. Among them, butyrate is thought to protect against colon carcinogenesis. However, few studies analyze the effects of butyrate, and other SCFA, on normal epithelial cells and on epithelial regeneration during disease recovery. Since there are controversial in vitro studies, we have explored the effects of SCFA on different biological processes. METHODS: We used both tumoral (HT-29) and normal (FHC) epithelial cells at different phenotypic states. In addition, we analyzed the in vivo activity of soluble dietary fiber and SCFA production in the proliferation rate and regeneration of intestinal epithelial cells. RESULTS: The effect of butyrate on epithelial cells depends on the phenotypic cellular state. Thus, in nondifferentiated, high proliferative adenocarcinoma cells, butyrate significantly inhibited proliferation while increased differentiation and apoptosis, whereas other SCFA studied did not. However, in normal cells or in differentiated cultures as well as in in vivo studies, the normal proliferation and regeneration of damaged epithelium is not affected by butyrate or SCFA exposure. CONCLUSION: Although butyrate could exert antiproliferative effects in tumor progression, its production is safe and without consequences for the normal epithelium growth.     

Effect of structural analogues of propionate and butyrate on colon cancer cell growth

The aim of this study was to evaluate the effects of natural short-chain fatty acids (butyrate, propionate, valerate, acetate) and structural analogues of butyrate and propionate on cell growth and apoptosis in three human colonic adenocarcinoma cell lines (HT-29, Colo-320, and SW-948). We have previously shown that mercapto- and bromo-analogues of butyrate and propionate compete with natural short-chain fatty acids for uptake in the colonocyte. Among naturally occurring short-chain fatty acids, butyrate was the most potent inhibitor of proliferation in all three cell lines. Propionate exhibited a weaker antiproliferative effect, while other short-chain fatty acids (valerate, acetate) were ineffective. Bromo-analogues of butyrate and propionate were more potent proapoptotic agents than butyrate. In contrast to butyrate, the analogues induced strand breaks on isolated supercoiled DNA, the effect being completely reversed by a DNA-protecting agent, spermine. We conclude that bromo-analogues of butyrate and propionate are more potent proapoptotic agents than butyrate in colon cancer cells in culture. Their effect may be a result of direct DNA damage.     

Mucin secretion is modulated by luminal factors in the isolated vascularly perfused rat colon

BACKGROUND: Mucins play an important protective role in the colonic mucosa. Luminal factors modulating colonic mucus release have been not fully identified. AIM: To determine the effect of some dietary compounds on mucus discharge in rat colon. METHODS: An isolated vascularly perfused rat colon model was used. Mucus secretion was induced by a variety of luminal factors administered as a bolus of 1 ml for 30 minutes in the colonic loop. Mucin release was evaluated using a sandwich enzyme linked immunosorbent assay supported by histological analysis. RESULTS: The three dietary fibres tested in this study (pectin, gum arabic, and cellulose) did not provoke mucus secretion. Luminal administration of sodium alginate (an algal polysaccharide used as a food additive) or ulvan (a sulphated algal polymer) induced a dose dependent increase in mucin discharge over the concentration range 1-25 mg/l (p<0.05 for 25 mg/l alginate and p<0.05 for 10 and 25 mg/l ulvan). Glucuronic acid and galacturonic acid, which are major constituents of a variety of fibres, produced significant mucin secretion (p<0.05). Hydrogen sulphide and mercaptoacetate, two sulphides produced in the colonic lumen by microbial fermentation of sulphated polysaccharides, did not modify mucin secretion. Among the short chain fatty acids, acetate (5-100 mM) induced a dose dependent release of mucus (p<0.05 for 100 mM acetate). Interestingly, butyrate at a concentration of 5 mM produced colonic mucin secretion (p<0.05), but increasing its concentration to 100 mM provoked a gradual decrease in mucus discharge. Propionate (5-100 mM) did not induce mucin release. Several dietary phenolic compounds (quercetin, epicatechin, resveratrol) did not provoke mucus discharge. CONCLUSIONS: Two algal polysaccharides (alginate and ulvan), two uronic acids (glucuronic acid and galacturonic acid), and the short chain fatty acids acetate and butyrate induce mucin secretion in rat colon. Taken together, these data suggest that some food constituents and their fermentation products may regulate the secretory function of colonic goblet cells.     

Colonic fermentation of dietary fibre to short chain fatty acids in patients with adenomatous polyps and colonic cancer.

Short chain (C2-C6) fatty acids are produced in the colon through bacterial fermentation of mainly dietary fibre. Butyrate (C4) possesses antineoplastic effects on human colon carcinoma cells, and epidemiological studies indicate that high fibre diets may reduce the incidence of colorectal cancer. The role of dietary fibre during colorectal carcinogenesis might therefore be related to its fermentation to butyrate. Faecal concentrations of total short chain fatty acids and concentrations and ratios of the individual C2-C6 fatty acids did not differ between 16 healthy controls, 17 patients with colonic adenomas, and 17 patients with colonic cancer. Comparison of the molar production velocities (mmol/l.hour) of total and individual short chain fatty acids from glucose, ispagula, wheat bran, and albumin in six and 24 hour faecal incubations showed no differences. The ratio of butyrate production to total short chain fatty acid production from fibre, however, was reduced in patients with colonic cancer and adenomas compared with healthy controls (ispagula, six hours: 6.4, 7.6, and 11.5% respectively, p = 0.005 and 24 hour: 9.1, 9.9, and 15.4%, p = 0.002; wheat bran, six hours: 9.9, 10.2, and 14.7% respectively, p = 0.06 and 24 hours: 15.1, 16.8, and 21.0%, p = 0.01). It may be that the low ratios of colonic butyrate formation combined with low fibre diets increase the risk of colonic neoplasia.     

Suppressing actions of butyrate on growth hormone (GH) secretion induced by GH-releasing hormone in rat anterior pituitary cells

We assessed the inhibitory effects of butyrate on the growth hormone (GH) secretion in order to investigate the cellular mechanisms in rat somatotrophs. Isolated anterior pituitary cells were cultured in DMEM for several hours, either in the presence (1, 3, or 10mM) or absence of butyrate, and then stimulated with 10(-7)M GHRH for 30 min, in the presence of butyrate at the concentrations used for the previous culture. The increase in GHRH-induced GH release was significantly reduced in a time-dependent and concentration-dependent manner in the cells previously cultured with butyrate. GH content (the sum of GH released into the medium induced by GHRH stimulation and the GH remaining in the cells after stimulation) was reduced by the culture of cells in the presence of butyrate, which was also inversely dependent on the concentrations used for the culture. Simultaneous addition of an L-type Ca(2+) channel blocker, nifedipine (10 pM), to the medium during 10(-9)M GHRH stimulation significantly reduced the stimulated GH release, which was further significantly decreased by a simultaneous addition of 10 mM butyrate. Butyrate blunted the GHRH (10(-9)M)-induced increase in cellular cyclic AMP and calcium ion concentrations, the activity of protein kinases (A and C), and GHmRNA expression. The expression of mRNA for GPR 41 and 43, known as receptors for short-chain fatty acids, was confirmed in the anterior pituitary cells. These findings suggest that butyrate inhibits GHRH-induced GH release as well as GH production, and the cellular inhibitory actions of butyrate occur in diverse cellular signaling pathways of rat somatotrophs.     

Effects of short chain fatty acids on a new human colon carcinoma cell line (LIM1215).

The effects of short chain fatty acids on a colon carcinoma cell line, LIM1215, have been studied. Of the four short chain fatty acids tested only butyrate at 1 mmol/l and 10 mmol/l and acetate at 10 mmol/l had significant effects on this cell line. The addition of butyrate to growth medium affected the growth rate and the production of alkaline phosphatase, dipeptidyl peptidase IV and carcinoembryonic antigen. Butyrate at a final concentration of 1 mmol/l increased the doubling time of the cells from 26 hours to 72 hours and decreased the cloning efficiency of the cells from 1.1% to 0.054%. Alkaline phosphatase concentrations increased rapidly in cells cultured in 1 mmol/l butyrate reaching peak levels after four days with alkaline phosphatase concentrations increasing more than six-fold. Levels of dipeptidyl peptidase IV and carcinoembryonic antigen were also increased after culture in butyrate containing medium. The number of alkaline phosphatase containing and dipeptidyl peptidase IV containing cells increased markedly in butyrate containing cultures. In contrast the number of mucus containing cells decreased in cultures grown in medium containing butyrate. This differentiating effect of butyrate on colon carcinoma cells may be relevant to the presence of butyrate in the colonic contents and the relationship between short chain fatty acids and fibre intake.     

Butyrate enema therapy stimulates mucosal repair in experimental colitis in the rat.

BACKGROUND--The short chain fatty acid (SCFA) butyrate provides energy for colonocytes, stimulates colonic fluid and electrolyte absorption and is recognised as an effective treatment for multiple types of colitis. AIM--To examine the impact of butyrate enema therapy on the clinical course, severity of inflammation, and SCFA stimulated Na+ absorption in a chronic experimental colitis. METHODS--Distal colitis was induced in rats with a trinitrobenzenesulphonic acid (TNBS) enema. Five days after induction, rats were divided into groups to receive: no treatment, saline enemas, or 100 mM Na-butyrate enemas daily. On day 24, colonic damage score and tissue myeloperoxidase (MPO) activity were evaluated. Colon was mounted in Ussing chambers and Na+ transport and electrical activities were measured during a basal period and after stimulation with 25 mM butyrate. RESULTS--In the untreated and the saline enema treated TNBS groups, diarrhoea and extensive colonic damage were seen, associated with increased tissue MPO activities and absent butyrate stimulated Na+ absorption. In contrast, in the butyrate enema treated TNBS group, diarrhoea ceased, colonic damage score improved, and tissue MPO activity as well as butyrate stimulated Na+ absorption recovered to control values. CONCLUSION--Butyrate enema therapy stimulated colonic repair, as evidenced by clinical recovery, decreased inflammation, and restoration of SCFA stimulated electrolyte absorption.     

口服葡苷聚糖对短链脂肪酸生成及其结肠细胞增殖的影响

目的观察水溶性纤维素葡苷聚糖对正常人肠道短链脂肪酸和结肠上皮细胞增殖变化的影响。方法，用高压液相和放射自显影技术分别测定葡苷聚糖服用前后肠道短链脂肪酸和结肠细胞增殖变化。结果（１）每日摄食８，１２ｇ葡苷聚糖可使大便中乙酸盐、丁酸盐和异丁酸盐含量明显升高；（２）结肠整条腺管标记指数在葡苷聚糖摄食后有显著变化，其程度与摄入量成正比；（３）葡苷聚糖能促进结肠腺管基底部细胞分化成熟。结论葡苷聚糖的发酵产物丁酸盐是结肠上皮最重要的能量来源；并对结肠上皮细胞的稳定和未分化细胞的成熟有重要意义。     

Vascular smooth muscle phenotype and growth behaviour can be influenced by macrophages in vitro

The effect of macrophages on rabbit vascular smooth muscle phenotype and proliferative ability was examined using ultrastructural morphometry. The volume fraction of myofilaments (Vv myo) in smooth muscle cells (SMC) from 9-week-old rabbit aorta in vivo was 39.5 +/- 1.2%. After seeding the enzymatically isolated SMC at 4 X 10(5) cells/ml in primary culture, the Vv myo was 38.9 +/- 1.2% on day 3 dropping to 29.9 +/- 2.0% by day 5. On day 6 the Vv myo was 29.2 +/- 1.8%, and the cells began to proliferate. Confluency was reached after less than 24 h proliferation and the Vv myo rose abruptly on day 7 to 36.9 +/- 1.9%. When the SMC were co-cultured with macrophages, the Vv myo fell to 31.2 +/- 0.9% on day 3 and to 25.9 +/- 0.5% on day 5 at which time cells commenced proliferation. Confluency occurred on day 6 but the SMC Vv myo did not rise throughout the rest of the culture period (27.4 +/- 1.8% and 26.9 +/- 1.3% on days 7 and 9, respectively) and the cells, unlike the controls, continued to proliferate, becoming multi-layered. Early phenotypic modulation in sparsely seeded SMC (8 X 10(4) cells/ml) co-cultured with macrophages was also found using fluorescent labelled antibodies to smooth muscle myosin. Measurement of proliferation by cell counts (and tritiated thymidine autoradiography) showed that macrophages stimulated SMC in primary culture to proliferate at a significantly greater rate than control cells grown alone in 5% whole blood serum (WBS). Proliferation of subcultured SMC co-cultured with macrophages was also stimulated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short-chain fatty acids inhibit the release and content of growth hormone in anterior pituitary cells of the goat

The effects of short-chain fatty acids (SCFA: acetate, propionate, and butyrate) on growth hormone (GH)-releasing hormone (GHRH)-induced GH secretion from pituitary somatotrophs were assessed on isolated anterior pituitary cells of goats. Cells were cultured in Dulbecco's modified Eagle's medium for 3 days, either in the presence (1, 3, or 10 mM) or in the absence of each SCFA, and then stimulated with GHRH (10(-12) to 10(-7) M) for 30 min, again in the presence of and at the concentration of SCFA used over the previous 3 days. In the cells cultured in the absence of SCFA, the addition of SCFA to the medium during the GHRH stimulation period did not significantly change GHRH-induced GH release. However, in cells cultured in the presence of either propionate (3 or 10 mM) or butyrate (1, 3, or 10 mM), the addition of SCFA to the medium during GHRH stimulation significantly reduced the GHRH-induced GH release. The inhibitory effects of SCFA were dependent on the concentrations of SCFA and were greater for butyrate than for propionate. In the cells cultured in the presence of butyrate, but not in the absence, the total GH production (the sum of the released GH and the remaining GH after stimulation) was also significantly reduced. The GHmRNA expression was reduced in the cells cultured with 10 mM butyrate, whereas it was enhanced by the stimulation with 10(-7) M GHRH. These findings suggest that propionate and butyrate may inhibit GHRH-induced GH release and GH production by caprine anterior pituitary cells.     

Inhibition of acetylcholine induced intestinal motility by interleukin 1 beta in the rat.

BACKGROUND/AIMS: The fact that raised interleukin 1 beta (IL 1 beta) concentrations have been found in the colonic mucosa of rats with experimentally induced colitis and of patients with inflammatory bowel disease indicates that this cytokine may participate in the disturbed intestinal motility seen during inflammatory bowel disease. This study investigated whether IL 1 beta could change the contractility of (a) a longitudinal muscle-myenteric plexus preparation from rat jejunum, ileum, and colon and (b) isolated jejunal smooth muscle cells. METHODS: Isometric mechanical activity of intestinal segments was recorded using a force transducer. Moreover, smooth muscle cell length was measured by image analysis. RESULTS: Although IL 1 beta did not affect jejunal, ileal, and colonic basal contractility, it significantly reduced contractile response to acetylcholine (ACh). This significant inhibition was seen only after 90 or 150 minutes of incubation with IL 1 beta. Pretreatment with cycloheximide blocked IL 1 beta induced inhibition of ACh stimulated jejunal contraction, suggesting that a newly synthesised protein was involved in the effect. NW-nitro-L-arginine (a nitric oxide synthase inhibitor) did not prevent the inhibition induced by IL 1 beta. Blocking neural transmission with tetrodotoxin abolished the IL 1 beta effect on jejunal contractile activity, whereas IL 1 beta had no effect on isolated and dispersed smooth muscle cells. CONCLUSIONS: IL 1 beta inhibits ACh induced intestinal contraction and this inhibitory effect involves protein synthesis but is independent of nitric oxide synthesis. This effect does not involve a myogenic mechanism but is mediated through the myenteric plexus.     

Fatty acid-induced effect on glucagon secretion is mediated via fatty acid oxidation

BACKGROUND: While the effect of fatty acids and ectopic triglyceride storage in pancreatic beta cells has been well-defined, only limited information is available on alpha cells. This study evaluates the long-term impact of fatty acids on alpha cell function and proliferation as well as fatty acid oxidation. METHODS: Clonal alpha cells were cultured with fatty acids in the presence of high glucose for up to 3 days. The influence of fatty acids on glucagon secretion, glucagon content and triglyceride accumulation from 24 to 72 h was investigated. After a - 72 h culture, cell proliferation, carnitine palmitoyl transferase-1 mRNA level and the effect of etomoxir were also elucidated. RESULTS: Fatty acids stimulated glucagon secretion and increased triglyceride accumulation in a time- and dose-dependent manner, but inhibited alpha cell proliferation. Lower concentrations (0.125-0.25 mM) of fatty acids significantly increased glucagon secretion at 48 and 72 h, but did not affect triglyceride content. However, a marked increment in triglyceride accumulation occurred in the presence of 0.5 mM fatty acids. Fatty acids caused an up-regulation of the expression of carnitine palmitoyl transferase-1 gene. Etomoxir (1 microM) reversed fatty acid-induced glucagon hypersecretion, but did not inhibit carnitine palmitoyl transferase-1 mRNA level. CONCLUSIONS: Our data indicates that compared with triglyceride accumulation, glucagon secretion is more sensitive to changes in fatty acid concentration. The effect of fatty acids on the glucagon response is mediated through their oxidation. The high carnitine palmitoyl transferase-1 gene expression and the accumulation of triglyceride may initially be a compensatory oxidation reaction to elevated fatty acids.     

Absorption and metabolism of octanoate by the rat colon in vivo: concentration dependency and influence of alternative fuels

BACKGROUND: Compared with short and long chain fatty acids, medium chain fatty acids (MCFAs) have been shown to provide the highest colonic absorption of substrate carbon. Moreover, colonic epithelial cells fulfil their basic energy requirements as easily from MCFAs as from short chain fatty acids. AIMS: To further characterise octanoate as a colonic luminal substrate, we determined in vivo the influence of (i) substrate concentration and (ii) alternative luminal fuels, on rat colonic transport and metabolism. METHODS: Segments of rat proximal colon (8 cm) were cannulated and perfused for 100 min with (14)C labelled octanoate. The right colic vein was also cannulated and venous blood analysed for total (14)C, (14)CO(2), and metabolites by scintillation counting and high performance liquid chromatography. RESULTS: Tracer appearance in mesenteric blood stabilised after 20-40 minutes of perfusion. Increasing luminal octanoate concentrations from 2 to 40 mM resulted in linear increases in total carbon absorption. Maximum CO(2) production was reached near 10 mM. A substantial proportion of octanoate was absorbed without being metabolised (59-94%). The luminal presence of a mixture of alternative fuels had no influence on either octanoate transport or metabolism. CONCLUSIONS: This study demonstrated substantial concentration dependent colonic absorption of octanoate, rendering this MCFA a potential and much needed high energy substrate for patients with compromised small bowel function. Moreover, octanoate meets the basic energy requirements of colonic epithelial cells in vivo as well as butyrate. This study also demonstrates the divergence of in vitro and in vivo data regarding fatty acid absorption and metabolism in the colonic epithelium.     

The effects of enterotoxins and short-chain fatty acids on water and electrolyte fluxes in ileal and colonic loops in vivo in the rat

The effect of cholera toxin (CT) and Escherichia coli heat-stable enterotoxin (ST) on the ileum and colon was examined in vivo in the rat in an attempt to clarify the effects of enterotoxins on colonic mucosa and to determine if these effects were influenced by short-chain fatty acids (SCFA). Both CT and ST induced similar changes in water and electrolyte fluxes, and the magnitude of these changes in loops of colon was similar to that observed in loops of ileum. The addition of luminal SCFA, acetate, propionate and butyrate did not influence the effect of either toxin in loops of ileum. However, in loops of colon exposed to CT, luminal butyrate (40 mM) largely reversed the effect of CT by converting net water secretion (mean +/- SE, -363 +/- 154 nl.cm-2.min-1) to net water absorption (470 +/- 194 nl.cm-2.min-1) and by significantly reducing the net secretion of sodium ions. In loops of colon exposed to ST, similar effects were observed although net water secretion (-784 +/- 114 nl.cm-2.min-1) was only partially reversed by butyrate (-318 +/- 102 nl.cm-2.min-1). In contrast to butyrate, acetate and propionate did not influence changes in colonic fluxes of water and sodium induced by enterotoxins. Oxidation of butyrate and glucose was observed to be depressed in colonocytes pre-exposed to CT but not to ST. In this model, colonic secretion induced by enterotoxins is similar to that observed in the ileum but differs from ileal secretion in its modulation by luminal butyrate.     

Effects of acetate and butyrate on the expression of leptin and short-form leptin receptor in bovine and rat anterior pituitary cells

The effects of acetate and butyrate on leptin and leptin receptor (OB-R) expression in bovine and rat anterior pituitary were examined. In bovine tissues, leptin gene expression using RT-PCR was observed in fat and anterior pituitary but not in liver. Isolated anterior pituitary cells cultured in Dulbecco's modified Eagle's medium (DMEM) for 3 days were further cultured for 48 h in DMEM containing 10 mM acetate or butyrate or without any fatty acids as control. Western blot analysis revealed that the abundance of leptin protein was greater in the presence of acetate and butyrate than that for the control culture. Leptin abundance was increased in a dose- and time-dependent manner in bovine anterior pituitary cells. However, leptin expression in rat cells, of which the basal level was much greater than that in ovine cells, was significantly decreased by the culture with butyrate. In addition, we studied the effects of both fatty acids on OB-R mRNA expression using semi-quantitative RT-PCR. The results showed that butyrate significantly decreased the expression in both bovine and rat cells. These findings indicate that acetate and butyrate enhance leptin expression in bovine, but not in rat anterior pituitary cells while butyrate suppresses OB-Ra expression in both rat and bovine pituitaries.