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| 2. |
- Granstam, S O, et al.
(författare)
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Effects of cigarette smoke and nicotine on duodenal bicarbonate secretion in the rabbit and the rat.
- 1990
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Ingår i: Journal of Clinical Gastroenterology. - 0192-0790 .- 1539-2031. ; 12 Suppl 1, s. S19-24
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Tidskriftsartikel (refereegranskat)abstract
- The effects of short-time exposure to cigarette smoke on duodenal mucosal bicarbonate secretion were studied in anesthetized rabbits and rats. The bicarbonate secretion was measured by continuous titration of recirculating luminal perfusate. In artificially ventilated rabbits, intermittent exposure to cigarette smoke during two 10-min periods caused a marked (approximately 40%) decrease (p less than 0.01) in duodenal bicarbonate secretion. After the exposures, secretion gradually recovered and had returned to the pre-exposure rate after 50 min. The decrease in secretion was associated with decreases in heart rate (approximately 15%) and blood pressure (approximately 30%) that, however, were of shorter duration. Neither reduced amounts of smoke (1/6 or 1/3) nor nicotine (25-1,000 micrograms/kg, intravenously) had any major effect on the bicarbonate secretion. In the spontaneously breathing rat, smoke was administered for 1-2 breaths every 30 s during a 5-min period. This exposure resulted in a significant (p less than 0.05) decrease in bicarbonate secretion and some increase in the blood pressure. Exposure to smoke had no effect on the secretion in rats with both splanchnic nerves cut, suggesting neural sympathetic mediation of the smoke-induced inhibition.
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| 3. |
- Holm, Lena, et al.
(författare)
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Duodenal alkaline secretion in rabbits : influence of artificial ventilation.
- 1990
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 138:4, s. 471-8
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Tidskriftsartikel (refereegranskat)abstract
- The effect of artificial ventilation on duodenal alkaline secretion and blood flow was studied in sodium pentobarbital-anaesthetized rabbits. A duodenal segment (approximately 3 cm) was cannulated in situ and continuously perfused with isotonic saline, and the bicarbonate secretion was titrated by pH-stat. Compared with the spontaneous breathing state, artificial ventilation improved the respiratory status of the animal, increasing Po2 and decreasing both Pco2 and plasma bicarbonate. Duodenal blood flow as measured with laser-Doppler flowmetry was not altered but the alkaline secretion was reduced. Pretreatment with the alpha 2-adrenoceptor antagonist yohimbine (0.5 mg kg-1 i.v., followed by 0.5 mg kg-1 h-1 i.v.) or the ganglionic blocker hexamethonium (10 mg kg-1 i.v.) did not affect the decline in duodenal alkaline secretion in response to artificial ventilation. Nor did these pretreatments affect the changes in plasma bicarbonate and Pco2 or significantly alter the blood flow. Increasing Pco2 in the respirator air increased the plasma Pco2 and bicarbonate concentration as well as the duodenal bicarbonate secretion. Pretreatment with the carbonic anhydrase inhibitor acetazolamide (80 mg kg-1 i.v.) reduced the bicarbonate secretion, and artificial ventilation induced a further reduction. Increasing Pco2 in the respirator in the animals pretreated with acetazolamide did not affect the bicarbonate secretion. Duodenal alkaline secretion was thus always reduced on artificial ventilation. The mechanism for this reduction does not seem to involve the sympathetic nervous system or the blood flow, but appears to be the consequence of alterations in the plasma concentration of bicarbonate and the plasma Pco2.
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| 4. |
- Holm, Lena, et al.
(författare)
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Microscopy of acid transport at the gastric surface in vivo.
- 1990
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Ingår i: Journal of internal medicine. Supplement. - 0955-7873. ; 732, s. 91-5
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Tidskriftsartikel (refereegranskat)abstract
- In vivo microscopy of the gastric surface, and pH-sensitive dyes, were used to study the movement of acid formed in the gastric crypts across the mucus layer adherent to the gastric surface and into the lumen. Rats were anaesthetized and the stomach gently exteriorized. When the pH-sensitive dye Congo red was applied luminally to stain the gel, predominantly red spots (pH greater than 5) and occasional blue spots (pH less than 3), located above the outlets of the crypts, were observed in spontaneously-secreting mucosae. Maximal stimulation of acid secretion (pentagastrin, 40 micrograms kg-1 h-1) resulted in the appearance only of blue spots, but the pH in the mucus gel between the crypts remained more alkaline, as indicated by pink staining. The fluorescence dye acridine orange was injected intravenously to an estimated blood concentration of 10(-5)M in another type of experiment. This dye is concentrated and secreted by the parietal cells. Pronounced fluorescence was observed within spots of the gastric surface corresponding to the outlets of the gastric crypts, but no fluorescence was detected outside these areas. The results obtained with both dyes strongly suggest that acid (and pepsin) is transported across the mucus gel only at restricted sites.
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| 5. |
- Schade, C, et al.
(författare)
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Hydrogen ion concentration in the mucus layer on top of acid-stimulated and -inhibited rat gastric mucosa.
- 1994
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Ingår i: Gastroenterology. - 0016-5085 .- 1528-0012. ; 107:1, s. 180-8
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND/AIMS: The gastric mucosa is covered by a continuous layer of bicarbonate-containing mucus gel; the question arises how acid, formed in the gastric glands, moves into the lumen.METHODS: The pH in the gastric mucus gel and gel thickness were measured in anesthetized rats with pH-sensitive microelectrodes (tip diameter, 1-5 microns).RESULTS: During pentagastrin (40 micrograms.kg-1.h-1) stimulation of acid secretion, the pH was higher in the gel than in the lumen (pH 2) up to a distance of 115 +/- 18 microns from the epithelial surface and maximal (pH 7.2 +/- 0.1) at the surface. A similar pH gradient was recorded at luminal pH 3. After omeprazole (10 mumol/kg) inhibition of endogenous acid secretion and with exogenous acid in the lumen, the pH profile was broader: 204 +/- 26 microns at luminal pH 2 and 231 +/- 63 microns at luminal pH 3. In contrast, the pH at the epithelial surface was lower (pH 6.8-6.9). The gel thickness (200-300 microns) was similar in all groups.CONCLUSIONS: The significantly higher surface pH in acid-secreting stomachs probably reflects better availability of interstitial mucosal bicarbonate. Bulk transport of secreted acid in channels created by the gland luminal hydrostatic pressure may additionally act to limit acidification of the mucus gel.
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