Patrick Tso

Metabolism of trinitrobenzene sulfonic acid by the rat colon produces reactive oxygen species

Recent studies have shown that intrarectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in ethanol or intramural injection of TNBS in saline produces an acute and possibly chronic colitis in rats. It has been assumed that interstitial TNBS initiates the inflammatory response via macrophage-mediated recognition and degradation of TNBS-modified mucosal cells and proteins. However, it is known that certain flavoproteins and/or reductants interact with compounds containing the nitro functional group to generate pro-inflammatory, nitrogen-centered free radicals and reactive oxygen metabolites. The objective of this study was to assess the ability of the rat colon, using either colon homogenates, isolated colonocytes, or intestinal interstitial fluid, to produce reactive oxygen species via enzymatic and/or nonenzymatic metabolism of TNBS. It was found that the addition of TNBS (1 mmol/L) to the 10,000 x g supernatant of rat colon homogenates increased the rate of superoxide production from normally undetectable levels to 2.6 +/- 0.23 nmol.min-1.mg protein-1. Addition of nicotinamide adenine dinucleotide, reduced form (NADH; 1 mmol/L) to colon homogenates containing TNBS significantly enhanced superoxide production to 10.4 +/- 0.9 nmol.min-1.mg-1. Similarly, addition of nicotinamide adenine dinucleotide phosphate, reduced form (NADPH; 1 mmol/L) to colon extracts containing TNBS produced an even further increase in the rate of superoxide formation to 25.2 +/- 1.1 nmol.min-1.mg-1. Addition of NADH or NADPH to the colon homogenate in the absence of TNBS produced no detectable superoxide formation, suggesting that TNBS was required for the enhanced oxidative metabolism. In a separate series of experiments, it was found that isolated colonocytes produced small but significant amounts of superoxide (3.15 +/- 0.6 nmol/2 x 10(6) cells) that were significantly increased in the presence of ethanol to 6.55 +/- 1.14 nmol/2 x 10(6) cells. Using purified preparations of two flavoproteins found in the rat colon, it was shown that the addition of TNBS (1 mmol/L) to purified NADH dehydrogenase or glutathione reductase increased the rate of superoxide formation by these enzymes from normally undetectable levels to 1.6 nmol/min and 1.2 nmol/min, respectively. In addition, it was found that intestinal interstitial fluid (lymph) initiated redox cycling of TNBS such that 28.1 +/- 1.6 nmol of oxygen was consumed per minute per milliliter of lymph. This increase in oxygen consumption was inhibited by the addition of superoxide dismutase and catalase. One possible metabolite involved in both mucosal and lymph-mediated metabolism of TNBS is ascorbic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracisternal injection of apolipoprotein A-IV inhibits gastric secretion in pylorus-ligated conscious rats

BACKGROUND/AIMSnFat feeding increases not only serum but also cerebrospinal fluid concentration of apolipoprotein (apo) A-IV, a protein produced mainly by the small intestine in the rat. We hypothesized that apo A-IV may have a central effect on gastric secretion.nnnMETHODSnGastric juice was collected by the pylorus ligation method. Rats underwent pylorus ligation and received intracisternal injection of apo A-IV under brief isoflurane anesthesia. Two hours after the injection, gastric juice was collected and gastric acid output determined.nnnRESULTSnIntracisternal injection of 0.5 microgram apo A-IV had no effect on gastric secretion. However, gastric acid secretion was significantly inhibited by intracisternal injection of 1 microgram apo A-IV. Furthermore, intracisternal administration of higher doses of apo A-IV (2.0 and 4.0 microgram) resulted in greater inhibition of gastric acid secretion in a dose-dependent manner. On the contrary, 4 micrograms of apo A-I intracisternally injected failed to inhibit gastric acid secretion. Intraperitoneal administration of 15 micrograms of apo A-IV did not alter gastric secretion.nnnCONCLUSIONSnThese results suggest that apo A-IV may act in the brain to inhibit gastric acid secretion. Apo A-IV might be a central enterogastrone, which is a gastric inhibitor produced by the small intestine in response to fat feeding.

Effect of intravenous administration of apolipoprotein A-IV on patterns of feeding, drinking and ambulatory activity of rats

To characterize the anorectic effect of apolipoprotein A-IV (apo A-IV), we examined the effect of apo A-IV on the patterns of feeding, drinking and ambulation of rats fed ad libitum. A single dose of 200, 135 or 60 micrograms was infused intravenously through a chronically indwelling right atrial catheter just before the dark period. Apo A-IV suppressed food intake by decreasing meal size, but did not affect the interval between meals, the speed of eating, or the latency to eat the first meal after infusion. The anorectic effect of apo A-IV was dose-dependent and was effective for about 3 h after the infusion. The anorectic effect of apo A-IV is specific because inactivation of apo A-IV abolishes its anorectic effect. The anorectic effect of apo A-IV is not shared by apo A-I. Apo A-IV had no effect on drinking behavior or ambulatory activity. The results seem to indicate that apo A-IV specifically decreases the meal size, which supports our hypothesis that apo A-IV may act as a physiological signal for satiation after the ingestion of a lipid meal.

The absorption and transport of lipids by the small intestine

Dietary lipid provides as much as 40% of the caloric intake in the Western diet. Triacylglycerol is the main dietary fat. The human small intestine is also presented daily with 11-12 g of phospholipid, predominantly phosphatidylcholine. The predominant sterol in the Western diet is cholesterol, which is derived from animal fat. Plant sterols account for up to 20-25% of total dietary sterol. This paper reviews our current understanding of the process and the factors that regulate the absorption and transport of different dietary lipids by the human small intestine.

Histamine and histidine decarboxylase are correlated with mucosal repair in rat small intestine after ischemia-reperfusion.

The aim of this experiment was to demonstrate whether histamine and histidine decarboxylase (HDC) contribute to mucosal repair in small intestine subjected to ischemia-reperfusion (I/R). The superior mesenteric artery was occluded for 15 min followed by reperfusion. In jejunal mucosa, histamine content and HDC activity increased after I/R. Histamine output in mesenteric lymph was also elevated after I/R. These increases in HDC activity, and mucosal and lymph histamine levels were suppressed by pretreatment of alpha-fluoromethylhistidine (alpha-FMH), a suicide inhibitor of HDC. alpha-FMH also attenuated the increase of ornithine decarboxylase (ODC) activity normally observed after I/R. Transport of dietary lipid into lymph markedly decreased at 24 h after I/R, yet it was restored to normal at 48 h after I/R. alpha-FMH inhibitor led to a sustained deficit in lipid transport at 48 h after I/R. This sustained functional impairment in alpha-FMH treated animals was associated with blunted responses of HDC activity and histamine content to I/R. Our results suggest that histamine and HDC contribute to the restoration in mucosal function observed at 48 h after I/R. This response may be related, at least in part, to stimulation of ODC activity by histamine.

Mechanism of action of intracisternal apolipoprotein A-IV in inhibiting gastric acid secretion in rats.

BACKGROUND & AIMSnWe recently showed that intracisternal injection of apolipoprotein A-IV (apo A-IV), a protein produced by the small intestine in response to fat, inhibits gastric acid secretion. The aim of this study was to investigate the mechanism of acid inhibition by central apo A-IV.nnnMETHODSnGastric acid secretion was determined in pylorus-ligated conscious rats. The effect of intracisternal injection of apo A-IV on gastric acid secretion stimulated by pentagastrin, bethanechol, or intracisternal thyrotropin-releasing hormone (central vagal stimulant) was examined. The effects of vagotomy, indomethacin, and adrenergic blockers on the acid inhibition of apo A-IV were examined to investigate the role of the vagal system, prostaglandin pathways, and adrenergic system.nnnRESULTSnIntracisternal apo A-IV significantly inhibited pentagastrin-, bethanechol-, and thyrotropin-releasing hormone-stimulated gastric acid secretion in a similar fashion. Inhibition of pentagastrin-stimulated acid secretion by apo A-IV still occurred even in vagotomized rats. Yohimbine but not indomethacin or propranolol eliminated apo A-IV--induced inhibition of acid.nnnCONCLUSIONSnIntracisternal apo A-IV inhibits gastric acid secretion through alpha 2-adrenergic receptors. The vagal pathway and the prostaglandin system are not involved in apo A-IV--induced acid inhibition.

The role of lipids in ischemia/reperfusion-induced changes in mucosal permeability in developing piglets

This study determined which nutrient component of formula may be responsible for changes in ischemia/reperfusion-induced mucosal permeability, as quantitated by the plasma-to-lumen clearance of 51Cr-ethylenediaminetetraacetic acid, in newborn piglets. Loops of jejunoileum in 1-day-old and 1-month-old piglets were perfused with predigested and bile acid-solubilized solutions of formula, lipid, protein, carbohydrate, delipidated formula, or fatty acid during 1 hour each of control, ischemia, and reperfusion. Luminal perfusion with formula or lipid led to significantly greater increases in mucosal permeability during reperfusion in newborn intestine than did carbohydrate or protein, whereas mucosal permeability in older animals was not different among solutions. Removal of all lipids from the formula abolished the increased mucosal permeability associated with reperfusion in newborn animals. Perfusion with oleate, a monounsaturated dietary fatty acid, led to still greater increases in reperfusion-associated permeability in newborn but not older intestine. The oleate and lipid perfusions also caused significantly increased mucosal permeability in the absence of ischemia. Thus, it appears that a lipid component of formula, probably a fatty acid, is responsible for the increase in mucosal permeability induced by ischemia/reperfusion in newborn intestine and also leads to increased mucosal permeability in the absence of ischemia/reperfusion. Investigation of the mechanism of these lipid-associated changes in mucosal permeability may provide a rationale for dietary modifications that may decrease the risk of mucosal injury during feeding and ischemic stress in immature intestine.

Fatty Acid-Induced Injury in Developing Piglet Intestine: Effect of Degree of Saturation and Carbon Chain Length

ABSTRACT: Luminal perfusion with the long-chain fatty acid (LCFA) oleate in concentrations similar to that found in premature infant formula produces a dose- and age-dependent mucosal injury in developing intestine. To investigate whether this lipid-induced phenomenon is a function of the degree of saturation and/or chain length of the fatty acid, 51Cr-EDTA plasma-to-lumen clearance was measured in jejunum and ileum of 1-d-, 3-d-, 2-wk-, and 1-mo-old piglets after perfusion with 5-mM solutions of different medium-chain saturated fatty acids and saturated and un-saturated LCFA. Mono- and polyunsaturated LCFA produced significant increases in jejunal permeability. In general, this effect was greater in piglets ≤2 wk old compared with 1-mo-old animals, but no differences were observed among the unsaturated LCFA within an age group. In contrast, the alterations in mucosal permeability induced by medium-chain fatty acids were overall more attenuated than those induced by LCFA. Our results suggest that developing intestine is vulnerable to the injurious effect of dietary fatty acids and that the lipid-induced changes in mucosal permeability appear to be a function of the fatty acid chain length. The degree of saturation of the fatty acid does not alter its cytotoxic effects.

Role of histamine receptors in intestinal repair after ischemia-reperfusion in rats

BACKGROUND/AIMSnPreviously, we showed that an elevated production of histamine promotes the healing of injured intestinal mucosa after ischemia-reperfusion. The aim of the present study was to determine whether histamine-mediated repair of the intestinal mucosa after ischemia-reperfusion involves the engagement of H1 or H2 receptors.nnnMETHODSnThe superior mesenteric artery was occluded for 15 minutes followed by reperfusion, and H1- or H2-receptor antagonists were infused intraduodenally. After ischemia-reperfusion, ornithine decarboxylase activity in the jejunal mucosa and lipid transport to mesenteric lymph were examined.nnnRESULTSnIn jejunal mucosa, ornithine decarboxylase activity markedly increased at 6 hours after reperfusion and remained elevated at 48 hours. The ischemia-reperfusion-induced increase in ornithine decarboxylase activity was attenuated (in a dose-dependent manner) by an H1-receptor antagonist (chlorpheniramine maleate) but not by an H2 antagonist (cimetidine). Intraperitoneal injection of an H3 antagonist (thioperamide) increased histamine output in mesenteric lymph and stimulated intestinal ornithine decarboxylase activity. Transport of dietary lipid into mesenteric lymph was depressed 24 hours after an ischemic insult, yet it returned to the normal level 48 hours after ischemia-reperfusion. The recovery of the lipid transport normally observed at 48 hours after ischemia-reperfusion was attenuated by the H1 antagonist.nnnCONCLUSIONSnThe beneficial effects of histamine on the repair of intestinal mucosa after ischemia-reperfusion results from the engagement and activation of the H1 receptor.

Circadian Rhythm of Ornithine Decarboxylase Activity in Small Intestine of Fasted Rats

Abstract The aim of this study was to determine whether the circadian changes in ornithine decarboxylase (ODC) activity of different segments of the small intestine were governed by factors other than food intake. First, the effects of fasting on mucosal ODC activity were examined. The results indicate that mucosal ODC activity in 24 hr and 48 hr fasted rats decreased significantly compared with ad libitum-fed rats. Second, the circadian rhythm of mucosal ODC activity was characterized by measuring mucosal ODC activity in fasted rats at four time points (09:00, 15:00, 21:00, and 03:00 hr; light period: 06:00–18:00 hr). The results from this study indicate that there is a detectable baseline ODC activity in different segments of fasting intestine. In duodenum, mucosal ODC activity was highest at 15:00 hr (light period), a time at which the rat was normally not eating. In jejunum and ileum, mucosal ODC activity increased between 21:00 and 03:00 hr (dark period). The observation that small intestine exhibits a distinct circadian rhythm of ODC activity in fasted rats suggests that not only food but also intrinsic factors can modulate physiologic oscillations in mucosal ODC activity.