Secretion and contribution to lipolysis of gastric and pancreatic lipases during a test meal in humans.

BACKGROUND: The aim of this study was to quantitatively evaluate the relative contributions to in vivo lipolysis of gastric and pancreatic lipases. METHODS: Gastric and pancreatic lipase secretions were measured, and their respective levels were determined in duodenal fluid during the digestion of a liquid test meal in healthy volunteers. Gastric lipase activity was clearly distinguished from that of pancreatic lipase by using both a specific enzymatic assay and an enzyme-linked immunosorbent assay. Lipolysis products were monitored throughout the digestion period. RESULTS: On a weight basis, the ratio of pancreatic lipase to gastric lipase total secretory outputs was found to be around four after 3 hours of digestion. The level of gastric hydrolysis was calculated to be 10% +/- 1% of the acyl chains released from the meal triglycerides. Gastric lipase remained active in the duodenum where it might still hydrolyze 7.5% of the triglyceride acyl chains. CONCLUSIONS: Globally during the whole digestion period, gastric lipase might hydrolyze 17.5% of the triglyceride acyl chains. In other words, gastric lipase might hydrolyze 1 acyl chain of 4, which need to be hydrolyzed for a complete intestinal absorption of monoglycerides and free fatty acids resulting from the degradation of two triglyceride molecules.

Gastric and pancreatic lipase levels during a test meal in dogs.

The levels of gastric and pancreatic lipases in the duodenum and the jejunum were measured during the digestion of a test meal in dogs. Using both a specific enzymatic titration and an enzyme-linked immunosorbent assay, it is shown for the first time that gastric lipase remains active in the duodenal and jejunal contents. An experimental device was set up for measuring the secretions and the intestinal flows of lipases during the digestion of a liquid test meal. In a dog equipped with gastric and duodenal cannulae, the secretion of gastric lipase was stimulated by food ingestion, reaching 3.0 +/- 0.3 mg/h (three times the basal secretion rate) during the 1st h of digestion. The total secretory outputs of gastric and pancreatic lipases recorded over a 3-h period of digestion were 7.2 +/- 1.2 mg and 18.7 +/- 1.2 mg, respectively.

Dog gastric lipase: stimulation of its secretion in vivo and cytolocalization in mucous pit cells.

Dog gastric lipase (DGL) secretion is stimulated in vivo by urecholine, pentagastrin, histamine, 16,16-dimethyl prostaglandin E2, and secretin. Under fasting conditions, DGL is irreversibly inactivated by gastric acid below pH 1.5; consequently, DGL output can be underestimated. This problem has been resolved by buffering the acid or by using an antisecretory drug such as omeprazole during stimulation. There is a clear parallelism between the secretion of DGL and of gastric mucus. This observation led to the present investigation of the cellular localization of DGL using immunofluorescence techniques. Results showed that DGL is cytolocalized in mucous pit cells of gastric glands. Pepsinogen is found in chief cells. To the authors' knowledge, this is the first description of an enzyme (gastric lipase) secreted by mucous-type gastric cells. In contrast to other species, gastric lipase of the dog is located in cardiac, fundic, and antral mucosae.

Intestinal absorption of fish oil in rats previously adapted to diets containing fish oil or corn oil.

A study was conducted to evaluate whether the composition of previous dietary fat affects the absorption and composition of lymph obtained after a meal of fish oil. Adult male Sprague-Dawley rats were fed diets containing either corn oil or fish oil (MaxEPA) for 2 weeks. They were then given intraduodenally a bolus of an emulsion of 0.5 ml of fish oil plus 0.5 ml of 20 mM sodium taurocholate. Intestinal lymph was collected from a cannula in the main intestinal lymph trunk for various times after oil administration. Rats proportion of the test dose fo fish oil than those fed corn oil. There was an effect of previous diet on the fatty acid composition of the lymph. Rats fed fish oil had a higher percentage of eicosapentaenoic and docosahexaenoic acids in the lymph lipids than those fed corn oil while those fed corn oil had a higher percentage of linoleic acid. These results rule out decreased intestinal absorption as a mechanism for the hypotriacylglycerolemic effect of dietary fish oils. They also indicate a significant contribution of endogenous lipids to the fatty acids in lymph.

Leukocyte-induced vascular protein leakage in cat mesentery.

The overall objective of this study was to determine whether leukocyte adherence and/or emigration is a prerequisite for the increased vascular protein leakage associated with acute inflammation. An in vivo preparation was used to monitor intestinal vascular protein leakage as well as polymorphonuclear leukocyte (PMN) adhesion and emigration in feline mesenteric microvessels exposed to platelet-activating factor (PAF) and leukotriene B4 (LTB4). Local intra-arterial infusion of PAF (4 ng/min) produced a fourfold increase in vascular protein leakage. A 50-fold higher concentration of LTB4 had no effect on vascular protein efflux. LTB4, however, did potentiate the PAF-induced vascular protein leakage. Both inflammatory mediators caused leukocytes to adhere to endothelial cells in postcapillary venules; however, leukocyte emigration was observed only in the presence of PAF. PAF-induced leukocyte adhesion and emigration and the increased vascular protein leakage were inhibited by a monoclonal antibody (MoAb IB4) directed against the common beta-subunit of the adhesive glycoprotein complex CD11/CD18. MoAb IB4 also prevented LTB4-induced leukocyte adhesion. Both PAF and LTB4 caused degranulation of cat PMNs in vitro, yet superoxide production was stimulated by PAF only. The data derived from these in vivo and in vitro studies indicate that leukocyte adhesion per se does not necessarily lead to increased vascular protein leakage and leukocyte emigration. Adhesion-dependent PMN functions such as emigration and superoxide production may play an important role in producing the alterations in vascular integrity observed in inflamed microvessels.

The acute pancreatotoxic effects of the plant nitrile 1-cyano-2-hydroxy-3-butene.

The effects of synthetic 1-cyano-2-hydroxy-3-butene (CHB), a racemic mixture of the (R)- and (S)-enantiomers, were studied in adult male rats. The compound given by gavage in olive oil at doses of 25-200 mg/kg causes toxic effects on the pancreas that resemble those seen when naturally occurring CHB is given to rats. At 6 h after dosing, pancreatic edema is seen with doses of 100 mg/kg and greater. The edema fluid had a high protein content, indicating a marked increase in macromolecular permeability of the pancreatic microcirculation. A loss of zymogen granules from the acinar cells and a lacy supranuclear vacuolation of the acinar cell cytoplasm was observed. At 4 h after dosing, pancreatic nonprotein thiols were depleted and rebounded at 24 h to three times control values. At 120 h nonprotein thiol levels decreased but were still elevated compared with control values. Glutathione-S-transferase activity in the pancreas had a similar pattern of change with initial reduction, followed by elevation at 24 h. In rats with pancreatic and biliary fistulas, intraduodenal CHB caused a transient early stimulation of pancreatic juice secretion followed by a return to control values in the case of the lower doses of CHB and depression of flows at larger doses. All doses of CHB caused a dose-related depression of protein concentration in pancreatic juice. Pancreatic juice flow was almost abolished at doses of 200 mg/kg. CHB caused a dose-dependent choleresis accompanied by a marked reduction in bile acid concentrations in bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on the mechanism of inhibition of intestinal chylomicron transport by Pluronic L-81.

This study explored further the hypothesis that intestinal cells have two pathways for producing large triacylglycerol-rich lipoprotein particles. The hydrophobic surfactant Pluronic L-81 (L-81) inhibits formation of chylomicrons (containing triacylglycerol synthesized from dietary fatty acids and monoacylglycerol, through the monoacylglycerol pathway), but not formation of very-low-density lipoproteins. L-81 does not inhibit lymphatic lipid transport during infusion of egg phosphatidylcholine, whose fatty acid is processed through the alpha-glycerol phosphate pathway and is transported in lymph in very-low-density lipoproteins. Thus, the first part of this study tested whether L-81 cannot inhibit the alpha-glycerol phosphate pathway, and thus L-81 can only affect chylomicron lipid secretion. Intestinal lymph fistula rats were infused with a lipid emulsion containing [1-14C]oleic acid, but no monoacylglycerol, to ensure that the oleic acid will be channeled to the alpha-glycerol phosphate pathway. Experimental rats received 1 mg/h of L-81 in their emulsion whereas control rats lacked L-81. Lymphatic triacylglycerol output, measured both chemically and radioactively, was markedly suppressed in the experimental rats as compared to the controls. Thus, these data indicate that the reason why lipid transport was unaffected by L-81 when egg phosphatidylcholine was infused was not because of the pathway used for the resynthesis of triacylglycerol from phosphatidylcholine. In the second part of this study, we measured the appearance time for chylomicron (in control rats) and for very-low-density lipoprotein (in L-81-treated rats). The appearance time is defined as the time between placement of radioactive fatty acid into the intestinal lumen and the appearance of radioactive lipid in the central lacteal. The average appearance time for the control rats was 10.8 min, which was significantly shorter than the 16.2 min in the L-81-treated experimental rats. This difference in appearance time further supports the hypothesis that chylomicron and very-low-density lipoprotein are packaged separately in the enterocytes and only the formation of chylomicron is inhibited by L-81.

Intestinal absorption and lymphatic transport of fish oil (MaxEPA) in the rat.

Adult male, chow-fed Sprague-Dawley rats were given intraduodenally a bolus of emulsion of 0.5 ml of fish oil (MaxEPA) or olive oil plus 0.5 ml of 20 mM sodium taurocholate. Intestinal lymph was collected from a cannula in the main intestinal lymph trunk for various times after oil administration. There was no difference in the absorption of either type of oil over 6 and 24 h, over which times about 40 and 70% of the administered dose was taken up. For MaxEPA, the flux of triacylglycerols remained at a basal level of 0.07 mumol/min for 30 min, after which it rose rapidly to a maximum of 0.87 mumol/min between 90 and 120 min. The flux was 0.4 mumol/min for the subsequent 4 h. After 30 min, the composition of the lymph triacylglycerols began to change to show the presence of large proportions of fatty acyl chains that were characteristic of fish oil, especially eicosapentaenoate (20:5(n-3] and docosahexaenoate (22:6(n-3]. The composition of the lymph remained fairly similar to that of the fish oil for up to 6 h, the last time point at which detailed analysis was done. The docosahexaenoate in the triacylglycerols of the fish oil was primarily in the sn-2 position of glycerol, whereas a more random distribution of eicosapentaenoate over all glycerol positions was found. The positional distribution of the acids in the lymph triacylglycerols was similar to that in the fish oil. There was no evidence of substantial chain elongation or shortening during absorption. The results indicate that fish oil is effectively absorbed from the rat intestine without substantial alteration in the acyl chains of the triacylglycerols.

Periosteal new bone formation and disseminated granulomatosis in a patient with Crohn's disease.

In a 20-year-old man, a proliferative periosteal new bone growth developed over the left forearm. Crohn's disease had been diagnosed the year before. Bone biopsy demonstrated granuloma formation. Biopsy specimens of skin lesions demonstrated granulomas as well. Bowel studies indicated active small intestinal inflammation with fistula formation. Despite the superficial resemblance to hypertrophic osteoarthropathy, it is believed that this case represents Crohn's disease with disseminated granulomatosis involving skin and periosteum.

Fusidic acid-induced hyperbilirubinemia.

A 72-year old man developed jaundice while on fusidic acid therapy for suspected osteomyelitis. Hyperbilirubinemia was predominantly of the conjugated variety and elevation in liver enzymes was mild and transient. Although serum bilirubin fell rapidly after fusidic acid was stopped, complete resolution of the hyperbilirubinemia took nearly a month. Other possible causes of jaundice were excluded. Light microscopy of a needle liver biopsy showed focal hepatocyte feathery degeneration, intracellular bile retention, and canalicular bile plugging, most prominent in perivenous regions. Electron microscopy revealed varying degrees of canalicular dilatation, loss of microvilli, and disruption of the canalicular membrane with vesicular bleb formation as well as canalicular bile plugs. Widening of the pericanalicular ectoplasmic zone with accumulation of cytoskeletal filaments was also noted. These findings are similar to those reported in experimental cholestasis induced by bile acids. Possible mechanisms of jaundice caused by fusidic acid are discussed.

Fate of 7,12-dimethylbenz(a)anthracene absorbed from the rat intestine and transported in chylomicrons.

Chylomicrons obtained from the thoracic duct of rats fed [3H]7,12-dimethylbenz(a)anthracene (DMBA), a polycyclic aromatic hydrocarbon, were infused intravenously into rats with bile fistulas. Over 17 hr, 55.9 +/- 3.2% (mean +/- SEM) of the radioactivity was recovered in bile and 6.7 +/- 0.5% in urine. Minor amounts were deposited in liver, kidneys and epididymal fat pads. Injection of DMBA in ethanolic solution gave a similar pattern, while biliary DMBA metabolites resulted in higher recovery in urine and lower recovery in fat. In conclusion, the major part of chylomicron DMBA is rapidly excreted via the biliary route, while a fraction is probably retained in adipose tissue.

Role of the lymphatic system in the transport of absorbed 7,12-dimethylbenzanthracene in the rat.

To determine the role of the intestinal lymphatic system in the absorption of a polycyclic aromatic hydrocarbon, 7,12-dimethylbenzanthracene, a radiolabeled preparation of the compound was given by intraduodenal infusion to rats in doses of 10 micrograms, 10 mg and 20 mg in olive oil solution. The hydrocarbon appeared to be absorbed from the intestine in a fractional manner, ca. 20% of the administered radioactivity being recovered totally in bile and intestinal lymph in 24 hr at all three dose levels. Biliary radiolabel accounted for 75-82% of combined recovery of radioactivity in bile and lymph with all three doses. The recovery of significant amounts of radiolabel in bile before the appearance of isotope in lymph, together with the fact that the biliary radiolabel greatly exceeded at all times the lymphatic recovery of isotope, suggests that an alternative pathway, presumably the portal venous route, is of major importance in the transport of the absorbed hydrocarbon.

Quantitative assessment of villous motility.

A videomicroscopic method was used to quantitatively analyze villous motility in the dog small intestine. The frequency and duration of villous contractions (retractions) were measured in the duodenum, midjejunum, and distal ileum under controlled conditions. A pronounced gradient of villous motility was evident along the bowel. The duodenum exhibited the highest frequency (7.3 +/- 0.1/min) and longest duration (2.6 +/- 0.1 s) of contraction; the jejunum exhibited an intermediate frequency and duration of contraction (4.0 +/- 0.1/min, 2.1 +/- 0.1 s), and the lowest values were measured in the ileum (2.0 +/- 0.1/min and 1.8 +/- 0.1 s). In contrast to the retraction movements, the frequency of pendular villous movements (whipping, swaying movements without shortening) was highest in the jejunum and lowest in the duodenum. The frequency and duration of villous contractions (retractions) remained relatively constant over a 2-h observation period. Reducing mucosal surface temperature from 38 to 30 degrees C caused the frequency of contraction to fall by 33% and the duration to increase by 106%. Varying the suffusate pH within the physiological range of 5.0-7.4 produced no significant effects on jejunal villous motility. Suffusion with glucose (140 and 280 mM) failed to alter villous motility. However, amino acid (15 and 30 mM) and fatty acid (10 mM) solutions significantly increased contraction frequency by 30-50% and 90%, respectively. The videomicroscopic method provides useful quantitative information, which should extend current knowledge regarding the regulation and physiological importance of villous motility.

Effect of experimental pancreatic growth on the content of xenobiotic-metabolising enzymes in the pancreas.

The concentration in pancreatic tissue and the total pancreatic content of three xenobiotic metabolising enzymes has been determined in two models of experimental pancreatic growth namely, cholecystokinin-octapeptide injections and soy flour feeding. No significant change in pancreatic concentrations of benzo(a)pyrene hydroxylase or glucuronyl transferase was detected. In both models of pancreatic growth, however, the concentration of glutathione-S-transferase was significantly reduced. It is possible that the reduction in this enzyme may be of some importance in determining the susceptibility of the pancreas to carcinogenesis observed with long term soy flour feeding.

The influence of bile on the bioavailability of polynuclear aromatic hydrocarbons from the rat intestine.

The mechanisms governing absorption of polynuclear aromatic hydrocarbons (PAHs) are important since these carcinogenic compounds occur as solutes in dietary lipids. These highly lipophilic compounds are well absorbed in the intestine. Bile salt micellar solubilization probably facilitates their transport across the unstirred water layer to the enterocytes. To study the role of bile in the intestinal absorption of PAHs, conscious rats with bile duct and duodenal catheters were given isotopically labelled 2,6-dimethylnaphthalene (DMN), phenanthrene, anthracene, 7,12-dimethylbenzanthracene (DMBA), and benzo[alpha]pyrene (BP); the recovery of radioactivity in bile and urine was measured. The PAHs were given intraduodenally in corn oil with or without exogenous bile. Cumulative recovery of radiolabel in bile and urine over 24 h was used to assess the efficiency of absorption of the hydrocarbons with and without bile. The following values for absorption without bile (as percentage of absorption with bile) were obtained: DMN, 91.6%; phenanthrene, 96.7%; anthracene, 70.8%; DMBA, 43.4%; BP, 22.9%. The values for anthracene, DMBA, and BP were significantly less than 100% (P less than 0.05); the values for DMN and phenanthrene were not significantly different from 100%. The dependence of the tricyclic compound anthracene (a structural isomer of phenanthrene) on bile for its absorption correlates with its lower water solubility. These results are consistent with the concept that the unstirred water layer presents a significant barrier to the absorption of this group of compounds and that micellar solubilization facilitates the uptake process.

Relations among canine intestinal motility, blood flow, and oxygenation.

Blood flow, arteriovenous O2 difference, and lumen pressure were measured in isolated loops of canine ileum. Ileal pressure was increased by an intra-arterial infusion of either Met-enkephalin or acetylcholine. Pressures were quantitated using a motility index (MI = mean of the pressure peaks divided by number of contractions per minute). Both Met-enkephalin and acetylcholine increased MI in a dose-dependent fashion. The highest MI achieved with acetylcholine was 37.9 mmHg, while Met-enkephalin produced a maximal MI of 8.1 mmHg. Ileal oxygen uptake increased when MI reached values greater than 6. There was a direct linear relationship between oxygen uptake and MI. Distension of the lumen in the absence of motility resulted in a decrease in oxygen uptake when lumen pressure reached 15-20 mmHg. The results of these studies indicate that contractions of intestinal smooth muscle can increase intestinal oxygen uptake and may contribute to the overall oxygen demands of the gut under conditions of fasting and feeding. Furthermore, large (greater than 20 mmHg) increments in lumen pressure during enhanced motility may compromise intestinal oxygenation.

Importance of interstitial matrix hydration in intestinal chylomicron transport.

We have shown previously that lymph flow has a profound effect on intestinal chylomicron transport. However, since lymph flow both determines the rate of convective movement of chylomicrons within the interstitium and reflects the degree of hydration of the interstitial matrix, we were unable to determine which factor was more important for the inverse relation between the chylomicron appearance time and lymph flow. In this investigation, we measured the chylomicron appearance time in rats with a normal lymph flow and expanded matrix (study A), in rats with a reduced lymph flow but expanded matrix (study B), and finally in rats with a dehydrated matrix (study C). The chylomicron appearance times were 11.7, 13.6, and 21.7 min for the rats from studies A-C, respectively. Thus, the data obtained from this study indicate that the matrix hydration may exert a more significant influence on chylomicron movement than lymph flow per se. In conclusion, the reduced chylomicron appearance time produced by expansion of the mucosal interstitium results from a diminished resistance of the interstitial matrix to chylomicron movement rather than a decreased transit time due to an enhanced convective flux of chylomicrons.