The effect of loperamide oxide on prostaglandin-stimulated fluid transport in rat small intestine

The effects of loperamide and loperamide oxide on basal and prostaglandin E2-stimulated fluid transport by rat small intestine have been investigated. In contrast to loperamide, loperamide oxide, when applied intraperitoneally, failed to inhibit either basal or prostaglandin E2-stimulated fluid transport. However, intraperitoneal administration of loperamide oxide following its incubation with the contents of the intestinal lumen under aerobic conditions resulted in an effective inhibition of fluid secretion. The activating material was present in the essentially non-particulate 3000 g supernatant fraction of the luminal contents and was heat-stable.     

Stimulatory effects of 5-hydroxytryptamine on fluid secretion and transmural potential difference in rat small intestine are mediated by different receptor subtypes

The rise in transmural potential difference (PD) and the fluid secretion induced by 5-hydroxytryptamine (5-HT) were measured in rat small intestine in-vivo. Both cisapride and ketanserin abolished the 5-HT-induced rise in systolic blood pressure mediated by 5-HT2 receptors. Cisapride inhibited the 5-HT-induced increases in the transintestinal PD, but over the same dose range it had no effect on the fluid secretion induced by 5-HT. In contrast, ketanserin caused a dose-dependent reduction in 5-HT-induced fluid secretion at doses that failed to influence the rise in PD. It is concluded that different receptors are responsible for the effects of 5-HT on fluid secretion and electrical activity in the rat small intestine.     

Sex-related differences in the effect of aluminum on calcium transport in the small intestine of the rat

Everted sacs of distinct segments of small intestine from male and female rats were incubated with 2 μM of aluminum (Al). In duodenum, Al significantly diminished calcium flux (JCa_ms) in cycling females (31%, P < 0.01) and in males (17%, P < 0.05). Incubation under anaerobic conditions nullified the inhibition of Al on JCa_ms both in male and in female duodenal sacs. Jejunal and ileal JCa_ms measured under aerobic conditions were not modified by the presence of Al in mucosal fluid compared to Al-free controls, neither in males nor in cycling females. In ovariectomized female rats treated with estrogen the studies of dose-response curves showed that the sensitivity to the effect of Al on JCa_ms was raised (the dose that produced half maximum response diminished) with increasing 17β-estradiol serum levels, without changes in the maximum response. In castrated male rats injected with testosterone, the effect of Al on duodenal JCa_ms was found to be independent of testosterone levels. In summary, our results demonstrated that the Al inhibition on duodenal JCa_ms was influenced by sexual hormone levels in females but was independent of them in males.     

Carrier-mediated transport of glycerol in the perfused rat small intestine

Studies using the closed loop and everted sacs of the rat small intestine recently prompted us to suggest that carrier-mediated transport is involved in the intestinal absorption of glycerol. Although it could be mediated by a novel carrier system, little information is available. The aim of the present study was to kinetically characterize carrier-mediated glycerol transport in the perfused rat small intestine to help in identifying the carrier involved and to explore the possibility that the carrier might be used as a pathway for oral drug delivery and a target for drug development. In situ single-pass perfusion was conducted using a 10-cm midgut segment of the male Wistar rat, and the absorption of [3H]glycerol was evaluated by its disappearance from the intestinal lumen. The absorption of glycerol was saturable and significantly reduced by removing Na+ from the perfusion solution, suggesting the involvement of a Na+-dependent carrier-mediated transport system. The concentration-dependent absorption profile was successfully analyzed by assuming Michaelis-Menten type carrier-mediated transport and simultaneous passive (diffusive) transport. The maximum transport rate (J(max)) was 77.0 pmol/s/cm2 and the Michaelis constant (K(m)) was 1.04 mM, giving a J(max)/K(m) of 7.39 x 10(-5) cm/s. The membrane permeability coefficient for passive transport (P(m,d)) was 6.89 x 10(-5) cm/s, slightly smaller than J(max)/K(m). Therefore, it could be the major mechanism of intestinal glycerol absorption in the low concentration range where carrier-mediated transport conforms to linear kinetics represented by J(max)/K(m). Furthermore, carrier-mediated glycerol transport was found to be inhibited by glycerol 3-phosphate, monoacetin and diglycerol, indicating that the carrier system may be shared by these structural analogues. Thus, the present study has successfully demonstrated and characterized carrier-mediated glycerol transport in the perfused rat small intestine which is a physiologically relevant model.     

The effect of diet on the 5-hydroxytryptamine content of the small intestine and other organs in rats and mice

In rats, a diet of meat or liver caused a rise in the amount of 5-hydroxytryptamine in the small intestine, an increase in the weight of the intestine and a 10-fold increase in anaerobic bacteria in the rectum. A diet containing added tryptophan did not affect tissue levels of 5-hydroxytryptamine in rats, but in mice there was a rise of 5-hydroxytryptamine in various tissues. The significance of these findings is discussed together with the possible role of intestinal bacteria in mediating the effects caused by a meat diet. No change was observed in the 5-hydroxytryptamine content of brain or in the distribution of argentaffin cells in the jejunum as a result of these diets.     

Investigation into the 5-hydroxytryptamine receptor mediating smooth muscle relaxation in the rat oesophagus.

1. An investigation has been made into the 5-hydroxytryptamine (5-HT) receptor mediating relaxation of rat oesophagus in preparations precontracted with carbachol. 2. In tissues treated with pargyline (100 microM) and in the presence of corticosterone (30 microM) and cocaine (30 microM) the potency of 5-HT and 5-methoxytyramine (5-MeOT) was not changed but the maximum response to these agonists was reduced. Thus there was no evidence of metabolism and/or uptake through an amine depleting mechanism. 3. The relaxant concentration-effect curves to 5-HT were shifted to the left in a concentration-related manner by isobutylmethylxanthine (1 and 10 microM), suggesting the involvement of adenosine 3':5'-cyclic monophosphate in these responses. 4. 5-HT produced concentration-related relaxations of rat oesophagus with an EC50 value of 0.24 microM. Several indole agonists were tested and the following rank order of potency of key agonists obtained: 5-HT greater than alpha-methyl-5-hydroxytryptamine = 5-carboxamidotryptamine (5-CT) greater than 5-MeOT. In contrast, 2-methyl-5-hydroxytryptamine, sumatriptan and 8-hydroxy-2-(di-n-propylamino) tetralin were weak or inactive. 5. The substituted benzamides, metoclopramide, cisapride, renzapride and R,S-zacopride acted as partial agonists, producing 60-70% of the 5-HT maximum. 6. The relaxation responses to 5-HT were neither inhibited by antagonists selective for 5-HT1 or 5-HT2 receptors nor by the 5-HT3 receptor antagonists, ondansetron, granisetron or MDL 72222. 7. The relaxation responses induced by 5-HT, 5-CT, 5-MeOT and renzapride were selectively inhibited by high concentrations of ICS 205-930 with pKB values of approximately 6.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hydroxyzine on the transport of etoposide in rat small intestine

Etoposide, an anti-neoplastic agent and a substrate of P-glycoprotein (P-gp), exhibits variable oral bioavailability. P-gp, the multidrug resistance gene (mdr1) product, has been considered as an absorption barrier against intestinal drug absorption. Terfenadine, an antihistamine, has been shown to be a P-gp inhibitor. The current study was designed to assess the effect of hydroxyzine, an antihistamine, on the transport of etoposide in the small intestine. Everted rat gut sacs were used to determine the absorption and exsorption of etoposide under different conditions, as rhodamine 123 was chosen to evaluate the role of P-gp in the drug interaction. The results showed that the transport of etoposide was significantly increased from the luminal site to the serosal site in the jejunum by 2- and 4-fold after 90 min in the presence of hydroxyzine and quinidine, respectively. A similar trend was observed in the ileal sacs. This in vitro exsorption study also demonstrated that hydroxyzine could reduce the efflux of etoposide to the luminal site in either jejunum or ileum. The effect of hydroxyzine on the pharmacokinetics of etoposide differed by the in vivo route of administration, thus assuming clinical importance for chemotherapeutic treatment.     

L-carnitine and carnitine ester transport in the rat small intestine

L-carnitine and its esters (acetyl-L-carnitine and propionyl-L-carnitine) at pharmacological doses (1, 5 and 10 mM) are absorbed by the rat jejunum by simple diffusion. Partition coefficients of carnitine esters determined in lipophilic media (diethyl ether/water and olive oil/water) are greater than that of L-carnitine. It would therefore seem that esters diffuse more easily through the lipid component of the intestinal barrier. The transport of acetyl- and propionyl-L-carnitine at pharmacological doses seems to be linearly and positively correlated with K+ transport but not with Na+ transport.     

Effect of auranofin on ion transport by rat small intestine

Auranofin, applied either mucosally or serosally, increased the potential difference and short-circuit current generated by stripped sheets of rat mid-intestine in a concentration-dependent manner. In-vivo auranofin induced a net fluid secretion, suggesting that the rise in electrical activity represented a stimulation of anion secretion. Removal of chloride or addition of frusemide inhibited the auranofin-induced increase in short-circuit current, indicating that chloride was the anion involved and in the case of serosal auranofin this was confirmed by direct measurement of ion fluxes. The effects of both mucosal and serosal auranofin were calcium-dependent. The gold component of the auranofin molecule is probably responsible for its secretory actions as these were mimicked by chlorauric acid. The ability of auranofin to stimulate intestinal secretion may contribute to its diarrhoeagenic action.     

Regulation of ion transport by 5-hydroxytryptamine in rat colon

1. 5-Hydroxytryptamine (5-HT) modulates the motility and secretion of the gastrointestinal tract. To examine the direct effect of 5-HT on the secretions of colonic epithelial cells, a short-circuit current was used to measure electrolyte transport in the rat stripped distal colon. A neuronal Na+ channel blocker and a cyclo-oxygenase inhibitor were routinely added in experiments to abolish the effects of the enteric nervous system and endogenous prostaglandin, respectively. 2. Basolateral application of 5-HT (10 micromol/L) induced an increase in the short circuit current (ISC). Removal of extracellular Cl-, HCO3- or both resulted in a 59.6, 76.4 and 90% reduction of 5-HT-elicited responses, respectively. The Ca(2+)-dependent Cl- channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) had no effect on the 5-HT-induced increase in ISC, but the selective cystic fibrosis transmembrane conductance regulator (CFTR) channel blocker glibenclamide (1 mmol/L) inhibited 5-HT-induced increases in ISC by approximately 92.9%. Removal of apical Na+ reduced the 5-HT-induced increase in ISC by 33.3%. 3. Basolateral pretreatment with 100 micromol/L bumetanide (an inhibitor of the Na(+)-K(+)-2Cl- cotransporter), 200 micromol/L DIDS (an inhibitor of the Na(+)-HCO3- transporter or the Cl-/HCO3- exchanger) or both decreased the DeltaISC induced by 5-HT by approximately 75.5, 59.0 and 86.3%, respectively. Removal of basolateral Na+ also reduced the current evoked by 5-HT. 4. The selective 5-HT4 antagonist GR113808 (1 micromol/L) totally abolished the 5-HT-induced increase in ISC, whereas 2-methyl-5-HT (100 micromol/L) induced a weak ISC response. 5. In conclusion, the present study has demonstrated that 5-HT can elicit Cl(-)- and HCO3- anion secretion and Na+ absorption by acting directly on colonic epithelial cells via 5-HT4 receptors.     

The action of R51619 on transport processes in the rat small intestine

R51619, an agent reported to release endogenous acetylcholine, increased the potential difference and short-circuit current across non-stripped, but not stripped sheets of rat mid-intestine. The response was abolished by both hexamethonium and atropine. R51619 stimulated fluid accumulation by intestinal loops in-vivo suggesting its predominant effect is to stimulate anion secretion. These results are consistent with R51619 releasing endogenous acetylcholine within the myenteric plexus to activate postganglionic cholinergic fibres which stimulate intestinal secretion via muscarinic cholinoreceptors.     

Effects of enflurane on 5-hydroxytryptamine transport in synaptosomes from rat brain

The administration of volatile anesthetics to laboratory animals has been reported to alter brain 5-hydroxytryptamine (serotonin, 5-HT) homeostasis. To examine a potential anesthetic action that could account for these observations, the effect of enflurane on 5-HT accumulation by rat brain synaptosomes was examined. Established techniques were used to prepare synaptosomes and perform uptake assays using [3H]5-hydroxytryptamine as substrate. Exposure of the synaptosomes to enflurane resulted in a concentration-dependent inhibition of serotonin uptake; the apparent I50 was 1.4 +/- 0.3 mM enflurane. Maximum inhibition was observed between enflurane concentrations of 2.6 and 4.3 mM, which inhibited uptake between 62 and 70%. The inhibition was rapid and reversible, and kinetic analysis of the inhibition was consistent with competitive inhibition by enflurane of 5-HT uptake with an apparent KI of 1.61 +/- 0.07 mM. In summary, exposure of synaptosomes to clinically relevant concentrations of enflurane resulted in a rapid, concentration-dependent, and reversible inhibition of 5-HT accumulation. These observations could represent a molecular interaction contributing to the anesthetic properties of enflurane and other volatile anesthetics.     

Comparative studies with 5-hydroxytryptamine and its derivatives in isolated, blood-perfused small intestine and ileum strip of the rat

The mode of actions of 5-hydroxytryptamine (5-HT) and its derivatives, tryptophan (TP), 5-hydroxytryptophan (5-HTP) and 5-hydroxyindole acetic acid (5-HIAA) was studied on the isolated, blood-perfused small intestine and isolated ileum strip of rats. In the isolated, blood-perfused intestinal preparations, 5-HT and 5-HTP injected into the superior mesenteric artery caused a monophasic fast contraction, while TP and 5-HIAA had no effects on the intestine. The contractile responses to 5-HT and 5-HTP were abolished by tetrodotoxin (TTX), hexamethonium (C6) and morphine, but were resistant to blockade of either atropine, methysergide or phentolamine. On the other hand, in the ileum strip preparations, 5-HT contracted the ileum, but its derivatives had no effects on the ileum. TTX, C6, morphine and atropine failed to prevent the contractile response to 5-HT, whereas methysergide effectively antagonized the response. The present results indicate that 5-HT acts by exciting intramural neuronal elements or by directly contracting the smooth muscle of the intestine. 5-HTP seems to act in the same manner as 5-HT.     

The distribution of 5-hydroxytryptamine and adenosinetriphosphate in cytoplasmic particles of the dog's small intestine

The distribution of 5-hydroxytryptamine, adenosinetriphosphate, and succinic dehydrogenase in sucrose homogenates of the dog's small intestine has been studied. The adenosinetriphosphate was present in two different layers which could be separated by density gradient centrifugation. The upper layer contained also much succinic dehydrogenase, but no amine; it is probably composed of mitochondria. The lower layer contained not only adenosinetriphosphate but also the major portion of the particle-held 5-hydroxytryptamine. The mean molar ratio, amine: adenosinetriphosphate, in the lower layer was 2.6. The experiments suggest that adenosinetriphosphate in the intestine is of importance in the storage of 5-hydroxytryptamine, resembling the function of adenosinetriphosphate in the storage of the catechol amines of the adrenal medulla.     

The effect of alpha-solanine on the active calcium transport in rat intestine

Solanine, an alkaloid isolated from potatoes was found to inhibit active calcium transport in rat duodenum both when added to the everted intestine sacs in vitro and when given to the rats in drinking water for 12 days. The inhibition by solanine of the active calcium transport in the rat intestine was found to be noncompetitive, the inhibitory constant being 25 microM.     

Inhibitory effect of 5-hydroxytryptamine on lipogenesis in rat adipose tissues

5-Hydroxytryptamine (5-HT) inhibited the incorporation of ¹⁴C from ¹⁴C-labelIed glucose, pyruvate, citrate and acetate into fatty acids but it did not inhibit the conversion of ¹⁴C from citrate and acetate into CO 2 , and the citrate conversion into glyceride-glycerol in epididymal and mesenteric adipose tissue from 24h-fasted rats. 5-HT stimulated the formation of lactate from glucose and pyruvate, and increased the ratio of lactate produced/pyruvate taken up. This ratio was similar to the NADH:NAD ratio. These results indicate that 5-HT inhibits fatty acid synthesis in rat white adipose tissue by mechanisms similar to those of the catecholamines.     

Calcium transport in rat small intestine in vitro and in vivo

Summary Intestinal calcium (Ca) transport was studied in the rat jejunum by the in vitro perfusion technique of Fisher and Parsons and in the tied loop in vivo. Mucosal uptake and absorption of Ca was examined under the following conditions: rising intraluminal Ca-concentrations (0.5–128 meq/l); inhibition of energy dependent metabolism (2,4-dinitrophenol, N₂, low temperature); net water flow, out of or into the intestinal lumen; addition of strontium (Sr); pretreatment with low Ca-diet and with 6-methyl-prednisolone.The concentration-dependent Ca absorption curve rose steeply at low Ca-concentrations but changed to a slowly rising straight line above 16 meq/l Ca⁺⁺. In contrast, Ca uptake into the intestinal wall was directly related to Ca concentration, was linear from the beginning and paralleled the straight part of the absorption curve.Ca absorption was decreased by inhibition of energy dependent metabolism, addition of Sr and pretreatment with prednisolone. Pretreatment with low Ca diet increased Ca absorption and direction of net water flow (solvent drag) had no effect on it.Mucosal uptake of Ca was similar to Ca absorption except that metabolic inhibition increased Ca uptake but decreased Ca absorption.These results are compatible with the concept of a passive mucosal uptake and of an active absorption of Ca at low intraluminal Ca concentrations with additional passive component at high Ca concentrations.Supported by the Deutsche Forschungsgemeinschaft.     

Inhibitory effect of 5-hydroxytryptamine on penile erectile function in the rat.

1. An increase in corporal pressure was elicited in pithed rats by stimulation of the sacral part of the spinal cord. This response was inhibited by intravenous injection of 5-hydroxytryptamine (5-HT) (ED50 = 28.5 +/- 2.2 micrograms kg-1). 2. The inhibitory effect of 5-HT was blocked by methysergide and methiothepin (each 1 mg kg-1), but not by ketanserin (0.02 mg kg-1), MDL 72222 (1 mg kg-1) or prazosin (0.1 mg kg-1). 3. An inhibitory effect on the corporal pressure response to spinal stimulation was also produced by 5-carboxyamidotryptamine (ED50 = 5.6 +/- 2.8 micrograms kg-1), but not by m-chlorophenylpiperazine (mCPP), RU 24969, 8-hydroxy-2-[di-n-propyl-amino]-tetralin (8-OH-DPAT) or fenfluramine (doses up to 1-2 mg kg-1). 4. Neither methiothepin (1 mg kg-1) nor clomipramine (1 mg kg-1) had any effect on the frequency-response curve for increase in corporal pressure by spinal stimulation. 5. The results indicate that 5-HT exerts an inhibitory action on penile erection by a peripheral mechanism. This effect may be mediated by vasoconstriction in cavernosal vessels, or inhibition of release of a vasodilator neurotransmitter. From the spectrum of agonist and antagonist responses, the receptor involved may be of the 5-HT1D subtype.     

Protective effect of lutein on ischemia-reperfusion injury in rat small intestine

Lutein is a carotenoid and it has antioxidant effects. Lutein may have a protective effect on ischemia reperfusion (I/R) injury induced by free radical species. However, little is known about the protective effect of lutein on I/R injury in vivo. The present study was undertaken to clarify the protective effects of lutein on I/R injuries in the rat small intestine. Administration of lutein before intestinal I/R attenuated the damage to villi and deciduation of enterocytes and suppressed the increase in lipid peroxide.