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The present investigation was designed to quantitatively assess the possible influence of countercurrent exchange on passive absorption from the small intestine of the dog. Villus blood flow was measured with a modification of the microsphere method. Simultaneously, the absorption from the gut lumen of five diffusible gases (H2, He, CH4, 133Xe, and CO) was determined. Villus blood flow averaged 0.247 +/- 0.03 (SEM) ml/min per g. The observed absorption of H2, He, CH4, and 133Xe was only 16.2 +/- 1.8, 12.8 +/- 2.3, 12.0 +/- 1.8, and 15.8 +/- 1.4 %, respectively, of what this villus blood flow could carry away if it reached perfect equilibrium with the luminal gases. This low absorption rate could result from diffusion limitation to absorption or countercurrent exchange. The diffusive permeability of the barrier seperating the luminal gases and villus blood flow was assessed by measuring the absorption rate of CO. Because absorbed CO binds tightly to hemoglobin, it cannot exchange, and when present in low concentrations its uptake is entirely diffusion limited. Knowledge of the diffusion rate through tissue of the unbound gases relative to that of CO made it possible to calculate the degree to which each of the unbound gases should equilibrate with villus tip blood. The percentage equilibration between lumen and blood at the villus tip for H2, He, CH4, and 133Xe was 99.7, 99.9, 75.6, and 36.0% , respectively. Each of these values greatly exceeded the percentage equilibration of blood leaving the villus (calculated from the observed absorption rate and villus blood flow) and indicated an exchange of 83.8, 87.2, 84.1, and 56.1% of initially absorbed H2, He, CH4, and 133Xe. This result is in accord with theoretical calculations which suggest that countercurrent exchange should be exceedingly efficient in the dog. The striking effect of countercurrent exchange on passive absorption in the dog differs from our previous studies in the rabbit where no exchange was demonstrated. This marked species difference may result from anatomical differences in villus architecture. The dog has long, densely packed villi while the rabbit has broad, widely spaced villi. In the dog, only the villus tips may equilibrate with the lumen, hence a countercurrent gradient may be established in the villus. The entire villus of the rabbit may equilibrate with the lumen and no gradient for countercurrent exchange can therefore be established.
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PMID:Quantitation of countercurrent exchange during passive absorption from the dog small intestine: evidence for marked species differences in the efficiency of exchange. 83 78

Different types of dietary fiber are fermented to various extents in vitro, but little is known about the effects of fiber on breath hydrogen and methane levels in vivo. Therefore, we studied the effects on breath hydrogen and methane of 15 g of guar, pectin, psyllium, soy polysaccharide, or cellulose in eight healthy subjects over a 12-h period. None of the fibers had a significant effect on breath hydrogen or methane concentrations, compared with the control (fasting). The four methane producers had lower breath hydrogen levels than the nonproducers 1 h after 15 g of lactulose (3 +/- 1 vs. 42 +/- 9, p less than 0.005) and 5-12 h after the different fibers (3.3 vs. 4.8 ppm; pooled SEM = 0.8; p less than 0.025). When the methane responses of the methane producers were expressed as increments relative to the control, there were small differences between treatments, with guar producing a larger response, 8.2 +/- 3.3 ppm, than cellulose, -2.9 +/- 2.3 ppm (p less than 0.05). The incremental methane responses of the different fibers in vivo were related to the previously reported production of propionic acid (r = 0.94, n = 5, p less than 0.02) and methane (r = 0.93, n = 4, NS) from in vitro fermentation of the same fibers. We conclude that methane producers have lower breath hydrogen levels than nonproducers. Purified fermentable and nonfermentable dietary fibers have no effect on breath hydrogen levels over 12 h in subjects previously consuming a normal diet. However, fermentable fibers may produce small increases in breath methane in methane-producing subjects.
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PMID:Effect of guar, pectin, psyllium, soy polysaccharide, and cellulose on breath hydrogen and methane in healthy subjects. 131 94

Hydrogen is produced during fermentation in the large intestine and may be excreted in breath and flatus or further metabolized by the flora. However, there is little information about total H2 excretion from different substrates or the extent to which it is metabolized in the colon. We have therefore measured total H2 and methane excretion in 10 healthy subjects using a whole body calorimeter. Breath gases were measured simultaneously with total excretion in response to lactulose, pectin, and banana starch. Metabolic activities of the predominant H2 consuming anaerobes (methanogenic, sulfate reducing, and acetogenic bacteria) were measured in fecal samples. Total H2 excretion on a starch and fiber-free diet was 35 +/- 6.1 mL/24 h +/- SEM. H2 from 7.5 g, 15 g, and 22.5 g lactulose was 88.1 +/- 22.4 mL, 227.0 +/- 60.7 mL, and 321.8 +/- 79.2 mL. Four of the subjects also excreted CH4, which was 51.3 +/- 5.5 mL, 97.3 +/- 18.4 mL, and 157.5 +/- 36.3 mL for the respective lactulose doses. H2 excretion was less in methanogenic subjects (7.9 mL/g lactulose) than in nonmethanogenic (17.3 mL/g), but total H2 excreted as, hydrogen + methane, was 34.9 mL/g. H2 from pectin (20 g) was 14.1% +/- 3.2% and from starch (22.2 g) 38.6% +/- 9.2% of an equivalent lactulose dose. Sixty-five percent of total H2 and CH4 was expired in breath at total excretion rates up to 200 mL/24 h. Over this the proportion decreased to 25% with an overall average of 58%. Only subjects with CH4 excretion in vivo showed methanogenesis in feces, whereas nonmethanogenic subjects showed high sulfate-reducing activity in feces (58.7 +/- 5.6 nmol 35SO4 reduced.h-1.g-1 wet wt vs. 7.9 +/- 2.0 nmol.h-1.g-1 in methanogens). Acetogenesis rates were very low in both groups. It was concluded that H2 excretion varies with different substrates. The proportion of H2 that is exhaled in breath is higher than currently accepted and varies with total excretion rate. Substantial amounts of H2 are consumed by methanogenic and sulfate-reducing bacteria.
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PMID:Production, metabolism, and excretion of hydrogen in the large intestine. 155 53

Imidazoleacetic acid (IAA) was unequivocally demonstrated in rat brain, human CSF, and human plasma by a gas chromatographic-mass spectrometric method that can reliably quantify as little as 8 pmol, i.e., 1 ng. Owing to tautomerism of the imidazole ring, IAA and [15N, 15N]IAA, the internal standard, each formed two chromatographically distinct isomers after derivatization of the ring nitrogens with either ethyl chloroformate or methyl chloroformate. The isomers of n-butyl(N-ethoxycarbonyl)imidazole acetate and n-butyl(N-methoxycarbonyl)imidazole acetate were identified by analysis with methane chemical ionization and electron impact ionization of molecular and fragment ions. The levels (mean +/- SEM) of free IAA were 140 +/- 14 pmol/g and 2.7 +/- 0.2 pmol/ml in brains of untreated rats and human lumbar CSF, respectively. Mean levels of IAA in brains of anesthetized rats, perfused free of blood, did not differ significantly from mean levels of anesthetized, nonperfused controls or from untreated rats. The source or sources of IAA in brain and CSF are unknown. Because IAA is a potent agonist at gamma-aminobutyrate receptors, it merits examination as a regulator in brain.
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PMID:Presence and measurement of imidazoleacetic acid, a gamma-aminobutyric acid agonist, in rat brain and human cerebrospinal fluid. 292 92

Dietary starch delivery to the colon and excretion in stools and the ability of unabsorbed carbohydrates to promote hydrogen and methane release in breath were evaluated in 6 volunteers during two 8-day periods on starch diets of 100 and 300 g, respectively. Significantly less starch was recovered from the terminal ileum by aspiration per 24 h during the low-starch period (4.1 +/- 0.3 vs. 9.5 +/- 1.1 g, mean +/- SEM, p less than 0.01). Unabsorbed glucose tended to rise during the high-starch period (2.7 +/- 0.8 vs. 1.1 +/- 0.3 g). Fecal outputs of starch, glucose, volatile fatty acids, and lactic acid were not significantly different during the two periods. Daily breath hydrogen excretion was unchanged (181.2 +/- 22.7 vs. 193.7 +/- 19.8 ml for the low- and high-starch periods, respectively), whereas breath methane excretion increased markedly in the three methane producers during the high-starch period (217.2 +/- 80.9 vs. 32.4 +/- 7.3 ml). Starch malabsorption in the healthy small intestine was moderate even with a high-starch diet and less than that previously estimated by indirect methods. Unabsorbed starch catabolism by the colonic flora does not seem to explain most of the breath hydrogen excretion.
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PMID:Starch malabsorption and breath gas excretion in healthy humans consuming low- and high-starch diets. 339 66

A single dose of haloperidol and reduced haloperidol has been found to exacerbate the dystonic response produced by U50,488H (trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) -cyclohexyl]-benzeacetamide methane sulphonate) in guinea-pigs [8]. The present study sought to correlate the behavioural effect of haloperidol and reduced haloperidol with their effect on inhibition of sigma binding sites in guinea-pig brain using receptor binding and semi-quantitative autoradiography. In the first experiments, groups of guinea-pigs were injected with saline (control, n = 12), haloperidol (0.1 and 1 mg/kg i.p., n = 5) or reduced haloperidol (0.1 and 1 mg/kg i.p., n = 5) 1, 3 and 10 days before, followed by U50,488H (10 mg/kg s.c.) and the effect on the dystonic response rated using a behavioural rating scale [8]. In the second experiments, animals (n = 5) were injected with saline, haloperidol and reduced haloperidol as above and killed 1, 3 and 10 days later, their brains removed, dissected and tissue sections processed for sigma binding site autoradiography using [3H]3-(3-hydroxyphenyl)-N-(n-propyl)piperidine ([3H]-3-PPP). Triplicate tissue sections were wiped using GF/C filters and radioactivity counted. Injection of haloperidol and reduced haloperidol 1, 3 and 10 days earlier exacerbated the dystonic response by decreasing the latency to maximal dystonia and increasing the duration of the response at each dose tested compared with saline-treated animals. These effects of haloperidol and reduced haloperidol on latency and duration were time-related since the effect at 1 > 3 > 10 days. In addition, [3H]-3-PPP binding was inhibited by haloperidol and reduced haloperidol in a dose-and time-related manner. For example, % inhibition of [3H]-3-PPP binding for haloperidol (1 mg/kg) > haloperidol (0.1 mg/kg) and % inhibition of binding (mean +/- SEM) produced by haloperidol (0.1 mg/kg) at 1 (96.1 +/- 2.4) > 3 (74.8 +/- 4.8) > 10 days (36.2 +/- 1.6). Similar results were obtained for haloperidol (1 mg/kg) and reduced haloperidol (0.1 and 1 mg/kg). [3H]-3-PPP autoradiography confirmed these binding data. The results indicate that the exacerbation by sigma ligands of the dystonia produced by U50,488H was associated with the degree of inhibition of [3H]-3-PPP binding.
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PMID:Haloperidol and reduced haloperidol-induced exacerbation of the dystonia produced by the kappa opioid U50,488H in guinea-pigs is associated with inhibition of sigma binding sites: behavioural and autoradiographical studies. 758 12

Several acutely acting antimigraine drugs, including ergotamine and sumatriptan, have the ability to constrict porcine arteriovenous anastomoses as well as the human isolated coronary artery. These two experimental models seem to serve as indicators, respectively, for the therapeutic and coronary side-effect potential of the compounds. Using these two models, we have now investigated the effects of avitriptan (BMS-180048; 3-[3-[4-(5-methoxy-4-pyrimidinyl)-l-piperazinyl[propyl]-N-methyl-l H-indole-5-methane-sulfonamide monofumarate), a new 5-HT 1B/1D receptor agonist. In anaesthetized pigs, avitriptan (10, 30, 100 and 300 micrograms.kg-1) decreased the total carotid blood flow by exclusively decreasing arteriovenous anastomotic blood flow; capillary blood flow was increased. The mean +/- SEM i.v. dose of avitriptan eliciting a 50% decrease (ED50) in the porcine carotid arteriovenous anastomotic blood flow was calculated to be 76 +/- 23 micrograms.kg-1 (132 +/- 40 nmol.kg-1) and the highest dose (300 micrograms.kg-1) produced a 72 +/- 4% reduction. In recent comparative experiments (DeVries et al. 1996), the mean +/- SEM ED50 (i.v.) of sumatriptan in decreasing carotid arteriovenous anastomotic blood flow was 63 +/- 17 micrograms.kg-1 (158 +/- 43 nmol.kg-1), with a reduction of 76 +/- 4% by 300 micrograms.kg-1, i.v. Both avitriptan (pD2; 7.39 +/- 0.09; Emax: 13.0 +/- 4.5% of the contraction to 100 mM K+) and sumatriptan (pD2: 6.33 +/- 0.09; Emax: 15.5 +/- 2.3% of the contraction to 100 mM K+) contracted the human isolated coronary artery. The above results suggest that avitriptan should be able to abort migraine headaches in patients, but may exhibit sumatriptan-like effects on coronary arteries. Initial clinical studies have demonstrated the therapeutic action of the drug in acute migraine.
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PMID:Effects of avitriptan, a new 5-HT 1B/1D receptor agonist, in experimental models predictive of antimigraine activity and coronary side-effect potential. 905 26

Diamond-like carbon (DLC) films have received much attention recently owing to their properties, which are similar to diamond: hardness, thermal conductivity, corrosion resistance against chemicals, abrasion resistance, good biocompatibility, and uniform flat surface. Furthermore, DLC films can be deposited easily on many substrates for wide area coat at room temperature. DLC films were developed for applications as biomedical materials in blood contacting-devices (e.g., rotary blood pump) and showed good biocompatibility for these applications. In this study, we investigated the surface roughness by Atomic Force Microscopy (AFM) and Hi-vision camera, SEM for surface imaging. The DLC films were produced by radio frequency glow discharge plasma decomposed of hydrocarbon gas at room temperature and low pressure (53 Pa) on several kinds of polycarbonate substrates. For the evaluation of the relation between deposition rate and platelet adhesion that we investigated in a previous study, DLC films were deposited at the same methane pressure for several deposition times, and film thickness was investigated. In addition, the deposition rate of DLC films on polymeric substrates is similar to the deposition rate of those deposited on Si substrates. There were no significant differences in substrates' surface roughness that were coated by DLC films in different deposition rates (16-40 nm). The surface energy and the contact angle of the DLC films were investigated. The chemical bond of DLC films also was evaluated. The evaluation of surface properties by many methods and measurements and the relationship between the platelet adhesion and film thickness is discussed. Finally, the presented DLC films appear to be promising candidates for biomedical applications and merit investigation.
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PMID:Engineering analysis of diamond-like carbon coated polymeric materials for biomedical applications. 1097 Dec 49

Snow is a divided medium that can adsorb atmospheric trace gases. Evaluating the impact of the snow cover on atmospheric chemistry therefore requires the knowledge of the specific surface area (SSA) of snow. This paper compares the results of three methods used to measure or estimate the SSA of four snow samples: CH4 adsorption at 77 K, optical microscopy (OM), and scanning electron microscopy (SEM, used only on two samples). Within error bars, CH4 adsorption and OM yield similar results on three of the four snow samples. Values for the 4th sample are within a factor of 2. For both samples where CH4 adsorption, OM, and SEM are used, all three methods yield similar results, but CH4 adsorption always has a better accuracy and a much better precision. Thus, despite its ease of use, estimates from OM images are often not accurate enough to monitor the evolution of snow SSA. The main sources of error in the OM method are the difficulty to determine snow crystal thicknesses and to take into account the topography of the snow crystal surface. The combination of CH4 adsorption and OM or SEM can provide useful information on the evolution of both the SSA and the shape of snow crystals. This will be useful to evaluate the respective contributions of adsorption/desorption and sublimation/condensation processes to the impact of the snow cover on atmospheric chemistry.
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PMID:Specific surface area of snow samples determined by CH4 adsorption at 77 K and estimated by optical microscopy and scanning electron microscopy. 1134 91

La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-delta)(LSCF) perovskite powders have been synthesised by solid-state reaction, co-precipitation, drip pyrolysis and citrate gel routes, and characterised using XRF, XRD, SEM and BET. Co-precipitation using oxalic acid or aqueous ammonia as precipitant failed to achieve the correct chemical composition. Perovskite structures were achieved in all other cases. Surface areas ranging from 0.6 to 17.4 m(2) g(-1) were obtained, which was reflected in the different microstructures observed. The citrate gel product exhibited a convoluted network morphology resulting in its large surface area. Thin-walled (approximately 200 microm) tubular membranes have been manufactured from the LSCF powders using viscous plastic processing. The tubes have been characterised using a custom-built gas analysis rig with on-line mass spectrometry. Porosity levels of the membranes were found to be very low (<0.1%). The spontaneous oxygen flux across the tubular membranes was determined as a function of temperature. Oxygen permeation rates ranged from 0.1 to 0.3 micromol cm(-2) s(-1) at 1273 K. The catalytic behaviour of the LSCF tubes towards methane oxidation has been studied using temperature programmed reaction and conventional catalytic measurements. The tubes favoured combustion reactions, with smaller amounts of partial oxidation and oxidative coupling products observed. Powder coatings have been incorporated to establish the effect of increasing surface area.
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PMID:Influence of synthesis route on the properties of doped lanthanum cobaltite and its performance as an electrochemical reactor for the partial oxidation of natural gas. 1545 40


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