Acetate absorption and metabolism in the rabbit hindgut.

Acetate disappearance from the loops of the hindgut in the rabbit was evaluated by measuring variations in the concentration of acetate in caecocolonic loops and differences in the arterial and venous plasma. In vivo metabolism in gut and liver tissues was studied after introduction of (1-14C) acetate into caecocolonic loops. The rate of disappearance from the loops was quantitatively significant and showed little variation irrespective of the location in the hindgut. Hindgut tissue metabolised acetate and the intensity of the metabolism varied with the segment studied. The distal position of the gut showed by far the highest acetate uptake. Radioactivity was found in a certain number of free amino acids, organic acids, and sugars. Acetate was mainly converted into aspartate and glutamate. These can be considered as 'stock forms' which can be diverted either towards oxidative metabolism or towards protein synthesis.     

Propionate absorption and metabolism in the rabbit hindgut.

Propionate disappearance from the loops of the hindgut in the rabbit was evaluated by measuring variations in the concentration of propionate in caecocolonic loops and differences in the arterial and venous plasma. In vivo metabolism in gut and liver tissues was studied after introduction of (1-14C) propionate into the caecocolonic loops. The rate of disappearance from the loops was always quantitatively significant but was greater in the proximal colon. Hindgut tissue metabolised propionate and the intensity of the metabolism varied with the segment studied; the proximal colon showed by far the highest propionate consumption. Radioactivity was found in a certain number of free amino acids, organic acids, sugars, lipid soluble substances and proteins. Propionate is an efficient respiratory fuel for the colonocyte and a good precursor for gluconeogenesis.     

Experimental lymphatic obstruction and fat absorption in the rabbit.

Using a previously published procedure of experimental abdominal lymphatic duct obstruction, we were unable to confirm increased faecal fat excretion after the operation. Nevertheless, the completeness of the obstruction and the huge dilatation of the lymph ducts of the villi have been verified. A spontaneous seasonal variation of faecal fat excretion has been observed in the rabbit with a maximum in October and November.     

NaCl absorption in the rabbit ileum. Effect of acid-base variables

In vivo and in vitro studies suggest that acid-base variables regulate ion transport in the rabbit ileum. The relative importance of these variables on active Na+ and Cl- absorption has not been defined. Isolated, stripped ileal segments were studied under short-circuited conditions in the Ussing flux chamber. Unidirectional 22Na and 36Cl fluxes were measured after changes in bathing solution pH, PCO2, and/or [HCO3-]. When pH was decreased from 7.6 to 7.1, net flux of Na+ increased from 0.1 +/- 0.7 to 2.6 +/- 0.7 mu Eq/cm2 per hour and net flux of Cl- increased from -2.0 +/- 0.9 to 1.3 +/- 0.6 mu Eq/cm2 per hour. These changes were rapid in onset, completely reversible, and accounted for by changes in mucosal-to-serosal fluxes of these ions. They were accompanied by small decreases in short-circuit current, but there were no changes in residual flux. These pH effects were not inhibited by the presence of luminal bumetanide (1 mmol/L), furosemide (1 mmol/L), hydroflumethiazide (1 mmol/L), or 4,4'-diisothiocyanostilbene-2,2'-disulfonate (1 mmol/L), or by the carbonic anhydrase inhibitor methazolamide (1 mmol/L). When data from all combinations of acid-base conditions were combined and analyzed by linear regression, pH was the only variable that correlated with mucosal-to-serosal fluxes (r = -0.84) and net flux (r = -0.85) for Na+, mucosal-to-serosal fluxes (r = -0.96) and net flux (r = -0.99) for Cl-, and short-circuit current (r = 0.97). These findings suggest that extracellular pH modulates active Na+ and Cl- absorption in the rabbit ileum.     

Diarrhea due to Escherichia coli in the rabbit: a novel mechanism.

A strain of Escherichia coli O15 (RDEC-1) isolated from several rabbits with diarrhea was examined to determine (1) whether the strain could produce diarrhea when administered by the orogastric route to other rabbits and (2) whether this strain was invasive or enterotoxigenic. Strain RDEC-1 produced diarrhea in 48 of 62 rabbits when given by the orogastric route in doses that ranged from 1.5 X 10(2) to 4 X 10(10) bacteria. The organism did not give a positive result in the 18-hr ileal loop or Serény tests and did not invade HeLa cells. Culture supernatants of strain RDEC-1 did not give positive results in the 6- or 18-hr rabbit ileal loop, suckling mouse, Y-1 adrenal cell, or Chinese hamster ovary cell assays. Fluorescent antibody staining of sections of intestine prepared in a cryostat revealed great numbers of E. coli strain RDEC-1 that adhered to the epithelial surface. It is evident that E. coli can produce diarrhea without being able to invade the mucosa or synthesize enterotoxin. Strains of E. coli similar to RDEC-1 may account for some of the E. coli-associated diarrhea that occurs in humans.     

Bile salt inhibition of motility in the isolated perfused rabbit terminal ileum.

The effects of bile on small bowel motility were studied in isolated, perfused rabbit terminal ileum. It was proposed that bile delivery into the distal ileum would inhibit ileal motor activity, by peptide YY (PYY) release and therefore the effect of luminal bile on motor activity was examined and PYY release measured. Luminal bile and taurocheodeoxycholic acid (10 mmol) inhibited ileal motor activity. Arterial infusion of venous effluents from a bile inhibited ileum suppressed motor activity in a second isolated ileum. This shows the presence of a humoral inhibitor of ileal motor activity. Luminal bile increased venous PYY concentrations (42.5 (8.5) to 502 (46.2) pmol/l; p < 0.01) and increased bile salt values (1.7 (0.36) to 88.6 (5.6) 10 mumol/l/l; p < 0.005). Arterial infusion of taurocheodeoxycholic acid at concentrations found in the venous effluent (100 mumol/l/l) suppressed motility (p < 0.001) but infusion of PYY at concentrations in the venous effluent (500.0 pmol/l) failed to inhibit motility. Furthermore, PYY antagonist, PYX 1, failed to reverse the bile induced inhibition of motility. Luminal bile salts inhibit terminal ileal motility and this is independent of PYY release. By slowing motility, bile salts may participate in their own absorption by the 'ileal pump' and in the 'ileal brake' mechanism.     

Intrapleural heparin or heparin combined with human recombinant DNase is not effective in the treatment of empyema in a rabbit model

OBJECTIVE AND BACKGROUND: The aim of this study was to investigate the effectiveness of intrapleural heparin or heparin combined with human recombinant DNase in the treatment of empyema. METHODS: Empyema was induced in rabbits with an intrapleural injection of 10(9)Pasteurella multicoda organisms in infusion agar via a surgically placed chest tube. Once empyema was verified, a blinded investigator administered drugs via the chest tube. There were three treatment groups each with six rabbits. One group was given 1000 IU heparin, a second group was given 1000 IU heparin plus 1 mg of human recombinant DNase via chest tube and the control group received saline. The rabbits received treatment every 12 h for a total of six treatments and the volume of each treatment was 3 mL. The animals were sacrificed at day 10 and the amount of empyema and pleural thickening was scored macroscopically on a scale of 0-6. RESULTS: The total volume of pleural effusion aspirated was significantly higher in the heparin group (25.8+/-10.7 mL) compared with either saline (8+/-8.9) or heparin plus human recombinant DNase (6.8+/-6.1) groups (P=0.003). The mean empyema and pleural thickening scores did not differ significantly between the groups (P=0.8, P=0.5 respectively). A weak correlation was found between total volume of aspirated pleural fluid and pleural parameters of white blood cell counts and LDH levels (r=0.546 and P=0.02, r=0.631 and P=0.02 respectively). CONCLUSION: The intrapleural administration of 1000 IU heparin alone or in combination with 1 mg of human recombinant DNase is no more effective than saline in the treatment of empyema in rabbits. Intrapleural heparin significantly increased the drainage of pleural fluid compared with the combination and saline group.     

Influence of sham feeding on salt and water absorption in the human jejunum.

Vagal stimulation induced by sham feeding in 11 healthy subjects was used to examine the possibility that the autonomic nervous system might be involved in the control of human jejunal absorption. Gastric acid secretion was measured from gastric aspirates corrected for recovery, and jejunal absorption was determined using a triple lumen perfusion technique. Sham feeding induced a significant increase in gastric acid secretion from 1.29 to 7.73 mmol/h (p less than 0.02). Jejunal absorption of water decreased significantly from 41.0 to 26.8 ml/30cm/h (p less than 0.02), sodium from 2.60 to 0.74 mmol/30cm/h (p less than 0.05, and chloride from 2.68 to 0.74 mmol/30cm/h (p less than 0.02). During the hour after sham feeding gastric acid secretion and jejunal absorption returned towards basal values. These results suggest that vagal stimulation may have influenced jejunal absorption of salt and water in man and supports the possibility that the autonomic nervous system has a physiological role in the control of intestinal mucosal function.     

Isolation of rabbit reticulocyte initiation factors by means of heparin bound to sepharose.

Passage of cell-free extracts of rabbit reticulocytes through heparin-Sepharose affinity columns results in the loss of the ability of the effluent to initiate protein synthesis. This is shown by the loss of response to added rabbit globin mRNA or to inhibitors of initiation of protein synthesis, such as heparin and aurin tricarboxylic acid, and by recovery of initiation activity by addition of protein retained and subsequently eluted from the columns. The effluent retains, however, the ability to elongate protein chains. Only 0.8% of the applied cell extract protein binds to heparin-Sepharose columns. This bound protein, which can be recovered by increasing the salt concentration of the eluting buffer, has initiation factor activity equal to that of a crude initiation factor preparation obtained from rabbit reticulocyte ribosomes by extraction with 0.5 M KCl. The protein patterns on polyacrylamide gels of the initiation factors prepared by either method are very similar and indicate a protein mixture, which may represent a complex. These data confirm that heparin interacts specifically with initiation factos, and indicate that heparin-Sepharose chromatography will simplify procedures for the preparation of initiation factors.     

Low-molecular-weight heparin vs. unfractionated heparin in percutaneous coronary intervention: a combined analysis.

This meta-analysis assessed the rates of the efficacy and safety endpoints with intravenous low-molecular-weight heparin (LMWH) compared with unfractionated heparin (UFH) in patients undergoing percutaneous coronary intervention (PCI). Subcutaneous LMWH has compared favorably with UFH, but limited experience exists with intravenous LMWH for immediate anticoagulation in PCI. The meta-analysis included data from eight randomized trials in which patients received LMWH (n = 1,037) or UFH (n = 978) during PCI. Seven additional nonrandomized studies/registries were analyzed to assess the efficacy and safety of LMWH during PCI. Efficacy endpoints were ischemic events (usually a composite of death, myocardial infarction, and urgent revascularization) and the safety endpoint was bleeding (major, minor, or all bleeding). In the randomized studies, LMWH was comparable with UFH in terms of efficacy (6.2% vs. 7.5%) and major bleeding (0.9% vs. 1.8%). The analysis of pooled data, randomized or not, suggests potential improved efficacy (5.8% vs. 7.6%) and reduced major bleeding (0.6% vs. 1.8%) with LMWH (n = 3,787) compared with UFH (n = 978). During PCI, intravenous LMWH without coagulation monitoring has the potential to be at least as safe and efficacious as intravenous UFH. Further studies of LMWHs in PCI are therefore required.     

Somatostatin stimulates sodium and chloride absorption in the rabbit ileum

The effect of somatostatin on ion transport in the rabbit ileum was determined. Somatostatin (a) decreased that short circuit current (Isc) (-1.0 +/- 0.2 mueq/hr . cm2) and potential difference (PD), (b) increased net Na and Cl absorption (+1.5 +/- 0.3 and +2.4 +/- 0.4 mueq/hr . cm2, respectively), and (c) increased tissue conductance (+5.1 +/- 1.3 mmhos/cm2). The increase in net Na and Cl absorption was primarily due to an increase in mucosal-to-serosal movement of these ions. Somatostatin had no effect on 3-0-methyl-glucose absorption, nor the increase in Isc produced by either 3-0-methyl-glucose or glucose. Phentolamine did not reverse the decrease in Isc produced by somatostatin and catecholamine depletion with reserpine or 6-OH-dopamine did not inhibit the somatostatin-induced decrease in Isc. The cholinergic agonists, carbachol and bethanechol, and no effect on somatostatin-induced decrease in Isc and atropine neither affected Isc nor blocked the effect of somatastatin on Isc. These studies demonstrate that somatostatin increased both Na Na and Cl absorption across rabbit ileal mucosa and suggest that these effects do not involve adrenergic or cholinergic agonists. Somatostatin may have a direct effect on the enterocyte.     

Phenamil inhibits electrogenic sodium absorption in rabbit ileum

Electrogenic Na absorption, independent of either nutrients or other ions, occurs in the rabbit ileum. However, unlike electrogenic Na absorption in the distal colon and other tight epithelia, this ileal transport system is not inhibited by amiloride. Because of this amiloride insensitivity, ileal electrogenic Na absorption has been poorly characterized. To more clearly delineate the underlying mechanisms of this pathway, we examined the effects of phenamil, an amiloride analogue, on ion fluxes and electrical parameters in rabbit ileum in vitro under short-circuit conditions. Phenamil has been shown to have a high affinity for Na channels, but minimal effect on Na-H exchange. Amiloride (10(-8) through 10(-4) M) had a minimal effect on short-circuit current. In contrast, phenamil induced a significant decrease in short-circuit current; the maximal effect was seen at 10(-4) M phenamil. There was an associated decrease in conductance at 10(-4) M phenamil. Ion flux studies were performed in normal, chloride-free and bicarbonate-free Ringer's solution; under each condition, 10(-4) M phenamil inhibited mucosal-to-serosal Na flux, net Na flux, and short-circuit current without significantly altering other fluxes. Phenamil did not inhibit the electrical response to either 10 mM glucose or 1 mM theophylline, indicating that the drug did not block either nutrient-coupled electrogenic Na absorption or electrogenic Cl secretion, and did not inhibit sodium-potassium-stimulated adenosine triphosphatase. These results demonstrate that electrogenic Na absorption in rabbit ileum may be blocked by the amiloride analogue phenamil, suggesting that, in this epithelium, Na absorption may occur via Na channels in which the amiloride-binding site has been significantly altered.     

局部释放肝素的生物降解性支架的初步实验研究

目的探讨携带肝素的生物降解性支架预防再狭窄的作用。方法应用已内酯和混旋丙交酯共聚物制成支架，并携带肝素，植入７只小型猪的颈动脉，观察不同时间的造影及病理改变。结果６只植入成功。植入成功者，１只因颈动脉破裂、支架内血栓形成死亡。３只动物分别于１个月（ｎ＝２）和２个月（ｎ＝１）处死，造影均未发现狭窄，光镜下仅见轻度内膜增生，扫描电镜观察支架表面已完全内皮化。２个月处死的另外２只动物造影显示狭窄，光镜下可见明显的平滑肌细胞增生。所有动物未见明显的异物反应。结论这种生物降解性支架，同时作为局部释放肝素的装置，可成功地植入颈动脉，对于其预防再狭窄的价值有待于进一步研究     

Short-chain fatty acid absorption in rabbit colon in vitro

Short-chain fatty acids are the predominant luminal anion in the colon and are generally absorbed rapidly in vivo. However, the mechanisms of in vitro transport of short-chain fatty acids have not been fully delineated. Therefore, we examined [14C]propionate fluxes in rabbit proximal colon under short-circuit conditions. There was minimal metabolism of propionate (less than 10%), permitting accurate flux measurements using a radioisotopic tracer. In a 20 mmol/L propionate Ringer's solution at pH 7.4, there was a significant rate of propionate secretion (-0.58 +/- 0.08 microEq.cm-2.h-1). Decreasing pH to 6.8 by decreasing bicarbonate concentration in the bathing medium resulted in increases in unidirectional fluxes but no change in net transport. Reversal of propionate secretion to propionate absorption was elicited by HEPES substitution for bicarbonate at pH 6.8 or by serosal addition of epinephrine, which increases apical Na(+)-H+ exchange in this epithelium. Propionate absorption was blocked by both amiloride, an Na(+)-H+ exchange inhibitor, and ouabain. Under basal conditions, there was a concentration-dependent increase in basal unidirectional propionate fluxes with no change in net transport as the concentration of propionate increased from 10 to 60 mmol/L. In contrast, a concentration-dependent saturation of epinephrine-stimulated propionate absorption was apparent. Transepithelial propionate gradients did not yield a significant diffusion potential. These results suggest that, in rabbit proximal colon, (a) there is bidirectional diffusion of propionate, most probably in the protonated rather than the ionized form; (b) a component of propionate transport is active and linked to electroneutral Na+ absorption through apical Na(+)-H+ exchange; and (c) changes in composition of the fluid bathing the proximal colon in vitro may significantly alter both rates and direction of short-chain fatty acid transport. Regulation of transcellular active transport may play an important role in colonic short-chain fatty acid conservation.     

Oral heparin results in the appearance of heparin fragments in the plasma of rats.

We have previously shown that angiogenesis inhibition and tumor regression can be accomplished by combinations of heparin or heparin fragments with cortisone [Folkman, J., Langer, R., Linhardt, R. J., Haudenschild, C. & Taylor, S. (1983) Science 221, 719-725]. Oral heparin was also effective in combination with cortisone. We now show that a single oral dose of [35S]heparin or [3H]heparin (15,000 units/kg) results in continuous release of radioactive material into the bloodstream for at least 12 hr. This is associated with the presence of anti-factor Xa activity at a level of approximately equal to 0.1 unit/ml. The radioactive material is identified as oligo-, di-, and monosaccharides by its behavior in chromatographic systems, its possession of anti-factor Xa activity, and the effect of treatment with bacterial heparinase. The heparin fragments are extensively metabolized to fragments without anti-factor Xa activity that are readily subject to urinary excretion.     

Intestinal absorption of low molecular weight heparin in animals and human subjects

INTRODUCTION: We had previously shown that the use of bile salts, which act as surfactants, facilitates the intestinal absorption of large molecules such as those of heparin and insulin. However, the bioavailability of unfractionated heparin (UFH) administered through the large intestine was low. The aim of the present study was to evaluate the absorption of low molecular weight heparin (LMWH) combined with bile salts through the gut mucosa in animals and human subjects. MATERIALS AND METHODS: LMWH (Fragmin, Kabi-Pharmacia, Stockholm) or UFH with or without sodium cholate (Sch) was administrated rectally in rats and healthy volunteers via a microenema. Absorption was estimated by the activated partial thromboplastin time (aPTT), the plasma anti-factor Xa activity and the plasma lipoprotein lipase (LPL) activation. RESULTS: In groups of 6 rats, LMWH at doses of 100--1,000 U with sodium cholate (10--20 mg/ml) was readily absorbed through the gut mucosa, as indicated by both, anti-factor Xa levels of up to 1 U/ml and a dose-dependent activation of LPL. The absorption was significantly superior to that of UFH with Sch or LMWH given without Sch (p < 0.001). The plasma anti-factor Xa levels in the 6 healthy volunteers who received a microenema containing 25,000 U of LMWH with 20 mg/ml of Sch were 0.38 U/ml at 15 min and 0.1 U/ml at 240 min. LPL activation and aPTT prolongation were also observed in these subjects. The plasma LMWH levels after rectal application were in the same range as those obtained after subcutaneous administration, however the elimination time (t 1/2) was shorter. There were no adverse reactions. CONCLUSIONS: Intestinal absorption of LMWH facilitated by Sch is both feasible and safe. A slow release formulation will be needed to prolong the plasma half-life.     

Haemorrhagic effect of enoxaparin, a low molecular weight heparin. Comparison with unfractionated heparin in humans.

The haemorrhagic effects of unfractionated heparin (UFH) and the low molecular weight heparin (LMWH) enoxaparin were investigated and compared in the gastric mucosa (haemorrhage induced by biopsy) and skin (haemorrhage induced by Simplate) of 12 healthy volunteers. Administration of UFH and LMWH (given in a dose of 75 anti-Xa U/kg intravenously) increased median gastric bleeding time (3.5 min) and geometric mean blood loss (11.5 microliters) to 19 min (p = 0.00003) and 54.1 microliters (p = 0.0021) after UFH and to 13 min (p = 0.008) and 29.0 microliters (p = 0.275) after LMWH. Median skin bleeding time (4.25 min) increased to 6.0 min after UFH (p = 0.003) and to 6.75 min after LMWH (p = 0.0008). Mean heparin activity in plasma was 20% higher after LMWH than after UFH. The calculated gastric bleeding time to heparin activity ratio was significantly lower for LMWH than for UFH (p < 0.05).