Effects of Potential Damaging Agents on the Microclimate-pH in the Rat Jejunum

doi:10.1002/jps.2600751209

Journal of Pharmaceutical Sciences

Volume 75, Issue 12, December 1986, Pages 1162-1165

https://doi.org/10.1002/jps.2600751209 Get rights and content

Abstract

This study was designed to determine the pH of the intestinal surface in the rat jejunum in an attempt to investigate the effect of potential damaging agents on the microclimate-pH. A significant pH gradient was observed between the mucosal surface and the bulk phase; however, the microclimate-pH usually ranged from 6.5 to 7.5, irrespective of the wide range in the bulk pH. When the bulk pH was either 7.3 or 4, the microclimate-pH was ∼6.7, while the microclimate-pH was ∼7.4 when the bulk pH was raised to 9. The distance of the PH gradient was found to be ∼900–1300 μm. After treatment with ouabain (10 mM) or amiloride (8 mM), or replacement of Na⁺ with Li⁺, the microclimate-pH significantly increased compared with the control (buffer solution). Chlorpromazine (2 mM) and ouabain also significantly increased the microclimate-pH, but at the same time, chlorpromazine decreased the bulk pH so that a more marked pH gradient was observed. Both aspirin (10 mM) and acetazolamide (80 mg/kg, iv) significantly decreased the microclimate-pH under the condition of the acidic bulk phase pH. N-Acetyl-L-cysteine (5%) induced marked changes in microclimate-pH, the direction depending upon the bulk phase pH. Neither taurocholic acid (10 mM) nor glucose (10 mM) significantly changed the microclimate-pH.

References and Notes (25)

I.N. Ross et al.
Gastroenterology
(1981)
G. Flemström et al.
Gastroenterology
(1983)
P.R. Sundaresan et al.
Biochem. Pharmacol.
(1978)
W.P. Ritchie
Gastroenterology
(1975)
T.H. Wilson et al.
Biochim. Biophys. Acta
(1957)
C.A.M. Hogben et al.
J. Pharmacol. Exp. Ther.
(1959)
J.A. Blair et al.
J. Physiol. (London)
(1975)
M.L. Lucas
J. Physiol. (London)
(1976)
M.L. Lucas et al.
Proc. R. Soc. London Ser. B
(1975)
M.L. Lucas et al.
Pflugers Arch.
(1983)

M.L. Högerle et al.

Naunyn-Schmiedeberg's Arch. Pharmcol.

(1983)

M.L. Lucas

Gut

(1983)

Cited by (22)

Evaluation of PepT1 transport of food-derived antihypertensive peptides, Ile-Pro-Pro and Leu-Lys-Pro using in vitro, ex vivo and in vivo transport models
2017, European Journal of Pharmaceutics and Biopharmaceutics
Citation Excerpt :
This is likely due to the continued presence of the acidic jejunal microclimate even in buffers of pH 7.4 and is in line with our findings. Previous studies demonstrated a minor increase in the rat jejunal microclimate pH due to increasing apical pH and indeed, the loss of acidity in the microclimate only occurred at an apical pH of 9 [52]. Addition of the bile salt, sodium deoxycholate did not influence the pH of the microclimate in the rat jejunum [54].
Ile-Pro-Pro (IPP) and Leu-Lys-Pro (LKP) are food-derived antihypertensive peptides which inhibit angiotensin-converting enzyme (ACE) and may have potential to attenuate hypertension. There is debate over their mechanism of uptake across small intestinal epithelia, but paracellular and PepT1 carrier-mediated uptake are thought to be important routes. The aim of this study was to determine their routes of intestinal permeability using in vitro, ex vivo and in vivo intestinal models. The presence of an apical side pH of 6.5 (mimicking the intestinal acidic microclimate) and of Gly-Sar (a high affinity competitive inhibitor and substrate for PepT1) were tested on the transepithelial apical to basolateral (A to B) transport of [³H]-IPP and [³H]-LKP across filter-grown Caco-2 monolayers in vitro and rat jejunal mucosae ex vivo. A buffer pH of 6.5 on the apical side enabled Gly-Sar to reduce the apparent permeability (P_app) of [³H]-IPP and [³H]-LKP, but this inhibition was not evident at an apical buffer pH of 7.4. Gly-Sar reduced the P_app across isolated jejunal mucosae and the area under the curve (AUC) in intra-jejunal instillations when the apical/luminal buffer pH was either 7.4 or 6.5. However, the jejunal surface acidic pH was maintained in rat jejunal tissue even when the apical side buffer pH was 7.4 due to the presence of the microclimate which is not present in monolayers. PepT1 expression was confirmed by immunofluorescence on monolayers and brush border of rat jejunal tissue. This data suggest that IPP and LKP are highly permeable and cross small intestinal epithelia in part by the PepT1 transporter, with an additional contribution from the paracellular route.
Enhanced Intestinal Absorption of Drugs by Activation of Peptide Transporter PEPT1 Using Proton-Releasing Polymer
2003, Journal of Pharmaceutical Sciences
Citation Excerpt :
The microclimate pH at the surface of the intestinal mucosa is an important factor for the absorption of various drugs and nutrients from the small intestine. Iwatsubo et al. reported that the microclimate pH remained about 7, despite the change in the bulk phase pH.32 In addition, it was indicated that microclimate pH was independent of bulk pH.33,34 On the contrary, it was reported that a reduction of the pH of the incubation medium from pH 7.0 to pH 6.0 increased mucosal uptake of glycylsarcosine by PEPT1.30 It seems likely that the pH in the microclimate as well as intestinal content can be decreased with the acidic polymer used in the present study.
Utilization of carrier‐mediated transport systems in the gastrointestinal tract to increase the bioavailability of drugs is of great interest. In the present study, an increased supply of the driving force for peptide transporter PEPT1 by utilizing a proton‐releasing polymer, Eudragit L100‐55, was employed to increase the intestinal transport activity. Intestinal absorption of zwitterionic cefadroxil and dianionic cefixime was studied in rats by using in situ ileal closed loops and by in vivo oral administration of the drugs concomitantly with Eudragit L100‐55. The results showed that Eudragit L100‐55 decreased the pH in the intestinal loops, and increased the disappearance of both cefadroxil and cefixime from the loops. In rats, the plasma concentration after oral administration was increased significantly by coadministration of Eudragit L100‐55, whereas a proton‐nonreleasing analogous polymer, Eudragit RSPO, did not have any effect. Furthermore, the increased absorption of cefixime caused by Eudragit L100‐55 was blocked by simultaneous administration of cefadroxil, a PEPT1 substrate/inhibitor, in a concentration‐dependent manner. These results demonstrate that improvement of intestinal absorption of peptide‐mimetics via a peptide transporter is possible by optimizing the transporter activity through coadministration of a proton‐releasing polymer that supplies the driving force for the transporter. © 2003 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2208–2216, 2003
Effects of aging on the microclimate pH of the rat jejunum
1996, Biochimica et Biophysica Acta - Biomembranes
The acidic microclimate layer in the vicinity of the cell surface of mammalian jejunum is important for absorption of some nutrients, such as small peptides and folate. The present study was undertaken to investigate the effect of aging on the cell surface pH (microclimate pH) of the jejunum of rats. The microclimate pH was measured in vitro in superfused preparations using single-barreled pH-sensitive microelectrodes filled with a liquid ion exchanger. The thickness of the microclimate layer was estimated by reading the distance of microelectrode advancements. The existence of a microclimate pH in the jejunum was confirmed in the senescent rats, but the value of the microclimate pH was significantly higher in the senescent (24 mo) rats (6.52 0.02) than in the young-adult (6 mo) rats (6.09 ± 0.01) (P < 0.01). Na⁺ removal from the perfusate or the addition of amiloride elevated the pH in the senescent rats as well as in the young-adult rats. The microclimate layer was slightly thinner in the senescent rats than in the young-adult rats. The acidity of the microclimate layer of intestinal surface is lower in senescent animals than in young-adult ones. One of reasons for this is the thinner mucus layer in senescent animals.
Effect of perfusate pH on the influx of 5-5′-dimethyl-oxazolidine-2,4-dione and dissociation of epidermal growth factor from the cell-surface receptor: the existence of the proton diffusion barrier in the Disse space
1994, Journal of Hepatology
The influx clearance (PS_inf.MID) of the weak acid 5,5′-dimethyl-oxazolidine-2,4-dione (DMO) was determined by the multiple indicator dilution method with the isolated perfused rat liver under various perfusate pH conditions, ranging from 6.4 to 7.6. Although the pH partition theory predicted an increase in influx clearance of ten times in proportion to the change in the unionized fraction of DMO, there was no measurable change in this value. The effect of medium pH on the steady-state cell/medium concentration ratio (C/M) ratio of DMO was also investigated using isolated hepatocytes. The C/M ratio increased while medium pH decreased, but this changes was less marked than predicted by the pH partition theory. Finally the pH dependency of the dissociation rate constant (k_off) of epidermal growth factor from its receptor was also investigated using both isolated rat hepatocytes and the perfused rat liver. When the extracellular pH was changed from 6.4 to 5.6, the k_off value of isolated hepatocytes increased 44 times, while that of the perfused rat liver increased only 9 times. Therefore, the effect of changing the extracellular pH on pH-dependent dissociation of epidermal growth factor from its cell-surface receptor was less in the perfused liver than in isolated hepatocytes. These findings, in addition to the well-known existence of the Na⁺-H⁺ exchanger on the sinusoidal membrane and the possible existence of the unstirred water layer in the Disse space, seem to suggest the existence of the proton diffusion barrier in the rat liver, which remains stronger in the perfused liver than in isolated hepatocytes
Epidermal growth factor as a regulatory hormone maintaining a low pH microclimate in the rat small intestine
1989, Journal of Pharmaceutical Sciences
This study was designed to determine the effect of epidermal growth factor (EGF) in the lumen on the pH of the intestinal surface in the rat jejunum, which is referred to as “microclimate-pH”. In the control experiment, a significant pH gradient was observed between the mucosal surface (~pH 6.8) and the bulk phase (~pH 7.3). The microclimate-pH was decreased by 0.2–0.6 pH units after addition of higher concentrations of EGF (3—100 nM) to the lumen. The microclimate-pH thus decreased recovers to the control value by replacing EGF with TES buffer, suggesting that the EGF effect is reversible. Considering that the Na⁺-H⁺ exchanger exists on the luminal membrane of the intestinal cells, the decrease in the microclimate-pH which was induced by EGF added to the luminal side may be due to the activation of Na⁺-H⁺ exchanger.
The effect of heat-stable Escherichia coli enterotoxin, theophylline and forskolin on cyclic nucleotide levels and mucosal surface (acid microclimate) pH in rat proximal jejunum in vivo
1988, BBA - Molecular Cell Research
The normally acidic mucosal surface pH of 6.24±0.02(30) in rat proximal jejunum in vivo is effectively neutralised by 30 min exposure to heat-stable Escherichia coli (STa) enterotoxin (14 μg/ml) to 6.80±0.07 (n = 5) or to a forskolin / theophylline combination (1 mM : 20 mM) to 7.10±0.07(7) while perfusion with Krebs-phosphate buffer alone without glucose left the mucosal surface pH unchanged at a pH of 6.21±0.02(9). Forskolin alone had no effect, and 20 mM theophylline moderately elevated the surface pH to 6.52±0.03(5). Theophylline, forskolin and their combination all elevated cAMP levels per mg tissue DNA above control values while STa enterotoxin was without effect. In contrast, all agents elevated cGMP levels per mg tissue DNA above control levels. These findings indicate that surface pH is only moderated affected by changes in cAMP levels and is affected to a much greater extent by altered cGMP levels.

View all citing articles on Scopus

View full text

ArticleEffects of Potential Damaging Agents on the Microclimate-pH in the Rat Jejunum

Abstract

Gastroenterology

Gastroenterology

Biochem. Pharmacol.

Gastroenterology

Biochim. Biophys. Acta

J. Pharmacol. Exp. Ther.

J. Physiol. (London)

J. Physiol. (London)

Proc. R. Soc. London Ser. B

Pflugers Arch.

Naunyn-Schmiedeberg's Arch. Pharmcol.

Gut

Article
Effects of Potential Damaging Agents on the Microclimate-pH in the Rat Jejunum