Down regulation of bisphenol A glucuronidation in carp during the winter pre-breeding season

Environmental pollution by bisphenol A is prevalent in many rivers. The influence of bisphenol A on the reproductive organs of carp has been demonstrated to be serious, especially in the winter pre-breeding season. Although bisphenol A is detoxified as bisphenol A-glucuronide in carp organs, principally the intestine, the seasonal variation in the efficiency of the detoxification is not known. To estimate the seasonal risk of bisphenol A in carp, we investigated seasonal changes in microsomal UDP-glucuronosyltransferase activity toward bisphenol A in male-carp. Seasonal elimination efficiency of bisphenol A was also examined by organ perfusion in everted intestine. No marked seasonal differences were observed in UDP-glucuronosyltransferase activity toward 1-naphthol, but high activity toward sex steroid hormones (testosterone and estradiol) was observed in the winter pre-breeding season. Low UDP-glucuronosyltransferase activity toward bisphenol A was indicated in winter. The addition of bisphenol A into the mucosal fluid of the everted intestine resulted in excretion of bisphenol A into the mucosal side of the intestine as the metabolite, bisphenol A-glucuronide. Excretion of bisphenol A-glucuronide from carp intestine was highest in summer (proximal intestine: 13.3 nmol; middle intestine: 8.3 nmol; distal intestine: 7.9 nmol) and lowest in winter (proximal intestine: 1.0 nmol; middle intestine: 1.0 nmol; distal intestine: 0.9 nmol). These results suggest that metabolism and excretion of bisphenol A in carp hepatopancreas and intestine are impaired by down regulation of UDP-glucuronosyltransferase activity in the winter pre-breeding season.     

Reconsideration of inhibitory effect of metformin on intestinal glucose absorption.

New evidence that metformin increases intestinal glucose metabolism has necessitated a re-examination of the effect of metformin on intestinal glucose absorption. Normal 18 h fasted mice received an intragastric bolus of metformin 2 h before preparation of everted gut sacs from the proximal, middle and distal regions of the jejunum and ileum. Net mucosal glucose transfer from the intestinal lumen into the tissue was reduced by 15 and 28% after 50 and 250 mg kg-1 metformin, respectively (ANOVA, P less than 0.05). Net glucose transfer into the serosal fluid was reduced by 12 and 70% after 50 and 250 mg kg-1 metformin respectively (ANOVA, P less than 0.05 and P less than 0.01). The inhibitory effect of metformin on both the mucosal and serosal glucose transfer mechanisms was greatest in the middle portion of the small intestine. The results suggest that metformin decreases intestinal glucose absorption in a dose-dependent manner by effects on mucosal and serosal glucose transfer.     

Concentration-dependent atypical intestinal absorption of cyclic phenylalanylserine: small intestine acts as an interface between the body and ingested compounds

Intestinal absorption of peptides in linear form has been studied extensively, but there is little knowledge of peptides in a cyclic form. In this report, intestinal absorption of cyclic phenylalanylserine (cyclo(Phe-Ser)), a precursor of gliotoxin, was studied in isolated rat small intestine as a model cyclic dipeptide. Absorption clearance (CLabs) decreased in the presence of glycylsarcosine, cephalexin or cephradine, substrates for H+/oligopeptide cotransporter (PEPT1). CLabs of cyclo(Phe-Ser) also decreased at 4 degrees C, thus indicating that cyclo(Phe-Ser) is in part transported by PEPT1. However, the Eadie-Hofstee plot of absorption revealed an atypical profile at lower concentrations of cyclo(Phe-Ser) (around 0.1 mM). Moreover, comparative experiments of absorptive and excretive transport showed that excretive transport from the serosal to mucosal side of isolated intestinal tissue at a 0.1 mM cyclo(Phe-Ser) was superior to absorptive transport from the mucosal side to the serosal side, and vice versa at a 1 mM cyclo(Phe-Ser). A kinetic model was constructed, in which cyclo(Phe-Ser) concentration for excretive transport was assumed to be at the binding site of excretive transporter, but not the unbound cytoplasmic concentration. These results as well as the results of kinetic analysis indicate that intestinal absorption consists of passive transport, carrier-mediated absorptive transport by PEPT1 and carrier-mediated excretive transport, resulting in atypical absorption. Although cyclic dipeptides have potentials as drugs, their intestinal absorption may be complex. The results of this study lead us to conclude that absorptive and excretive transport by the small intestine acts as an interface between the body and ingested compounds.     

Intestinal absorption of digoxin and interaction with nimodipine in rats

It is known that digoxin, which is a liposoluble cardiac glycoside, is well absorbed from intestine. In the present study, the absorption rates of digoxin from rat duodenum and the proximal and terminal parts of small intestine were determined in vitro. The isolated everted duodenum and intestinal sacs were put into oxygenated Tyrode solution at 37 degrees C. The Tyrode solution on the outer, mucosal side of intestinal segments contained 0.3 microM digoxin. Samples from the internal serosal side of the intestinal sacs were taken at 30, 60 and 120 min after the start of the experiments. The concentration of digoxin in the samples of fluid were determined using a radioimmunoassay method. The effect of nimodipine (0.1 and 0.2 mM) on digoxin absorption was also evaluated on the terminal segment of rat intestine. The interaction of nimodipine (0.5 mg/kg) and digoxin (0.2 mg/kg) was investigated in vivo when they were given perorally to rats. The duodenal absorption of digoxin was lower than in the small intestine. The highest absorption occurred in the terminal segment of the small intestine. Nimodipine increased the absorption of digoxin from the terminal segment of intestine in vitro, while it did not affect the serum digoxin concentration in vivo.     

Intestinal Handling of Bisacodyl and Picosulphate by Everted Sacs of the Rat Jejunum and Stripped Colon

Abstract: Bisacodyl (BIS) is the acetic acid di-ester of the laxative diphenol 2-(4,4′-dihydroxydiphenyl)methylpyridine. A HPLC-method which permits the simultaneous determination of BIS and its monodesacetylated (MONO) as well as totally desacetylated (DES) form, has been used to study the intestinal handling of BIS (20 nmol/ml), when the compound was incubated for 60 min. at the mucosal side of the preparations specified. In the jejunal mucosal fluid, BIS disappeared completely in short time, and there was a nearly equivalent rise in DES. MONO was transitory present. Hydrolysis was also rapid in mucosal fluid which had been in contact with jejunal sacs for 30 sec., but BIS was stable in blank incubations. Hydrolysis of BIS was slower by colonic than by jejunal sacs, and all three molecular forms were present during incubation. It seemed still slower in mucosal fluid which had been in contact with colonic sacs for 5 min. BIS just as DES accumulated in the jejunal and colonic serosal fluid mainly as conjugates (>95%), and DES was in all cases the only unconjugated metabolite present. Drug accumulation in jejunal serosal fluid was the same whether BIS or DES was added. However, more drug seemed to accumulate on the serosal side of colonic sacs when incubated with BIS instead of DES. In similar experiments with picosulphate, which is the sulphuric acid di-ester analogue of BIS, free DES was not detected in the mucosal fluid during incubation. The amounts of laxative accumulating in the serosal fluid were less than 1/10 of those observed with BIS.     

In vitro effects of wood creosote on enterotoxin-induced secretion measured electrophysiologically in the rat jejunum and colon.

Secretory diarrhea occurs when the balance between intestinal absorption and secretion is disturbed by excessive secretion caused by enterotoxins produced by the pathogen. Wood creosote has long been used as a traditional antidiarrheal remedy. The goal of our study was to extend our knowledge about the antisecretory action of wood creosote against Escherichia coli enterotoxin-induced secretion in the small intestine and colon. Experiments were performed in mucosal sheets of rat jejunum and colon which were stripped of the external muscle layers to eliminate interactions with smooth muscle activity and local blood flow. Mucosal sheets were placed in modified Ussing chambers and hypersecretory conditions were induced by heat-labile (LT) or heat-stable (STa) E. coli enterotoxins added cumulatively (0.01-10 microg/ml) to the mucosal bathing solution. Intestinal secretion was monitored electrophysiologically as transmucosal short circuit current (Isc). LT induced a concentration-dependent increase in Isc in the rat jejunum, with no effect in the colon. In contrast, STa induced a significant increase in colonic Isc, without causing any change in Isc across the jejunum. In separate experiments the effects of increasing concentrations of wood creosote (0.1-50 microg/ml), added to the mucosal or serosal bathing solution, were examined against the secretory responses induced by LT or STa. In the small intestine the antisecretory activity of wood creosote against LT-induced secretion was more potent following serosal application, whereas in the colon wood creosote inhibited STa-induced secretion with equal potency following either serosal or mucosal addition. In summary, our findings demonstrate that wood creosote possesses antidiarrheal activity suppressing E. coli enterotoxin-induced secretion in both the small intestine and colon.     

Naphthol metabolism: glucuronide conjugation and transport by the rat intestine in vitro

[¹⁴C]Naphthol was converted to water-soluble ¹⁴C-labeled metabolites by everted sacs of rat small intestine. The extent of conversion to metabolites and release to the bathing medium was greater for sacs from cranial (80%) than for sacs from caudal (60%) small intestine. The concentration of metabolites was always greater in serosal than in mucosal fluids. This concentration gradient increased from the cranial to the caudal end of the intestine. Net ¹⁴C transport to the serosal fluid was entirely as metabolites and was associated with the volume of water transported. The principal metabolites were glucuronide conjugates of naphthol which were hydrolyzed by β-d-glucuronidase. Naphthyl-β-d-glucuronide appeared to be the principal metabolite in the recovered mucosal and serosal fluids and tissues. The quantities of metabolites synthesized by sacs from the various regions of the intestine were not notably different when either pH 7.4 or pH 6.5 medium was used. The tissue concentration of ¹⁴C and quantity of metabolite transferred to serosal fluid in the pH 7.4 and pH 6.5 media were slightly different. The mechanism for the apparent uphill transport of metabolites was not apparent. The results have been compared to those from previous investigations where [¹⁴C-naphthyl]N-methylcarbamate was studied and provide greater insight into the intestinal metabolism of this naphthol-containing pesticide.     

Intestinal Absorption of Stable Cyclic Glycylphenylalanine: Comparison with the Linear Form*

The absorption, especially the stability and transportability, of the cyclic peptide cyclic glycylphenylalanine (cyclo(Gly-Phe)) and the linear peptides glycylphenylalanine, glycyl-d -phenylalanine and phenylalanylglycine have been studied in rat small intestine. Linear peptides were degraded on the mucosal side and only glycyl-d -phenylalanine appeared on the serosal side. However, cyclo(Gly-Phe) was stable on the mucosal side and appeared on the serosal side. Furthermore, the absorption clearance of cyclo(Gly-Phe) was higher than that of glycyl-d -phenylalanine. In the presence of the peptidase inhibitor bestatin, the degradation of linear peptides was reduced and linear peptides appeared on the serosal side, but only phenylalanylglycine, which is transported by the oligopeptide transporter, was absorbed faster than cyclo(Gly-Phe). The absorption clearance of cyclo(Gly-Phe) was reduced as its concentration was increased from 125 μm to 500 μm . Furthermore, the absorption clearance of cyclo(Gly-Phe) at 125 μm was reduced at 4°C or in the presence of glycylsarcosine and cephalexin, which are transported by the oligopeptide transporter. These results indicated that cyclo(Gly-Phe) was stable enough to be absorbed and was transported in part by the oligopeptide transporter rather than completely by passive diffusion.     

Ciprofloxacin permeability and its active secretion through rat small intestine in vitro

The biopharmaceutical aspect of the fluoroquinolones-metal cations interaction, which reduces antibacterial agents bioavailability and the mechanism of the fluoroquinolone intestinal efflux are still poorly understood. The purpose of this work was to gain further insights into these two issues by measuring the permeability of ciprofloxacin through the rat small intestine in side-by-side diffusion chambers using different incubation media and transport inhibitors. The permeability of ciprofloxacin from the mucosal to the serosal side was low. It was not influenced by the different concentrations of Ca(2+) and Mg(2+) in the donor solution. The active efflux of ciprofloxacin was the highest in the region of the rat small intestine excised proximal to the ileo-caecal junction or when the pH value of the incubation saline was slightly acidic. Thus ciprofloxacin appears to be transported in its cationic or in its zwitterionic form. The efflux was not inhibited by verapamil, benzbromarone or quinidine, which were added to the mucosal side of the intestinal tissue. It was however inhibited by quinidine added to the serosal side. The active secretion is therefore most probably a consequence of the organic cation transporter 1 activity at the basolateral membrane of enterocytes.     

Disposition of formononetin via enteric recycling: metabolism and excretion in mouse intestinal perfusion and Caco-2 cell models

The purpose of this study was to determine the absorption and metabolism of formononetin using the mouse intestinal perfusion model, mouse intestinal homogenate, and the Caco-2 cell culture model. In the perfusion model where upper and lower small intestine were perfused simultaneously, absorption of formononetin was rapid and dimensionless effective permeabilities of formononetin (2.53-2.90) were similar to those for rats. Moreover, the amounts of sulfates excreted in mouse intestine (8-11 nmol/30 min/10 cm) were significantly higher than those for rats whereas the amounts of glucuronides excreted (7-10 nmol/30 min/10 cm) were comparable. Small amounts of formononetin glucuronide but not sulfate were found in mouse bile, but the total amounts were 120 times less than those for rats. Multidrug-resistance-related protein (MRP) inhibitors (leukotriene C(4) plus MK-571, C(26)H(26)ClN(2)O(3)S(2)) significantly decreased the excretion of glucuronide and sulfate in mouse intestine (52-74% for glucuronide, 13-26% for sulfate) and in Caco-2 cells (92% for glucuronide, 37% for sulfate). They also inhibited formation of conjugates in intestinal homogenate (approximately 60% for glucuronide, approximately 30% for sulfate) and Caco-2 cell lysate (approximately 92% for glucuronide, approximately 37% for sulfate). Organic anion transporter (OAT) inhibitors (estrone sulfate plus dihydroepiandrosterone sulfate) did not significantly change the excretion of formononetin conjugates in either model, even though they significantly decreased the formation of both. In conclusion, our study showed that formononetin has similar absorption in rat and mouse intestine, but metabolism was species-dependent. The mouse perfusion model may have an advantage over the rat intestinal perfusion model for flavonoid disposition studies in that both sulfates and glucuronides are excreted, as shown in humans.     

Uptake,Conjugation and Transport of Laxative Diphenols by Everted Sacs of the Rat Jejunum and Stripped Colon

Abstract: Phenolphthalein (PHEN), desacetylbisacodyl (DES) and oxyphenisatin (OXY) were incubated with everted sacs of the rat jejunum and stripped descending colon; the mucosal and serosal fluid were analysed with respect to free and conjugated diphenol by means of HPLC. Conjugates were measured as the amount of free diphenol in completely hydrolyzed samples less the amount before hydrolysis. A study with double-sided administration of PHEN revealed that diphenol uptake from and conjugate output to both sides followed a rectilinear course for 15–90 min. A standard incubation time of 60 min. was chosen for the subsequent experiments, in which the diphenols were administered at the mucosal side at a low and a high concentration. Diphenol uptake, i.e. the amount of free diphenol administered less the amount recovered at the mucosal side, varied in an order (PHEN>DES>OXY) which seems to be inversely related to the order of water solubility of the compounds. Tissue accumulation and conjugate output relative to uptake varied with the dose, and from one compound to another. At low initial concentration (20 nmol/ml), the compounds were transferred to the jejunal and colonic serosal fluid almost entirely as conjugates (≥95%); the transfer rates followed, qualitatively, the same order as above. In jejunum, more conjugates were released to the mucosal than to the serosal side; in colon the distribution was reversed. Increasing the dose to 100 nmol/ml caused a corresponding increase in uptake, but relative output decreased and tissue accumulation increased; thus demonstrating capacity limitation. With PHEN, the ratio of conjugated:free diphenol on the serosal side remained essentially unchanged; with DES in particular, but also with OXY the ratio decreased. These findings may be interpreted to mean that in case of PHEN capacity limitation is linked to conjugate efflux, while DES and OXY may be poor substrates for glucuronide formation as well. Experiments with serosal side administration like the double-sided PHEN experiments verified the dissimilar conjugate distribution in jejunal and colonic sacs; the phenomenon is to some extent discussed in the text. Identity tests gave evidence that the conjugates were mainly monoglucuronides.     

替加氟新型前体脂质体小肠吸收试验研究

目的　考察替加氟新型前体脂质体的小肠吸收情况。方法　采用大鼠离体小肠吸收法 ,UV法测定黏膜液及浆膜液中替加氟浓度 ,以浓度对时间作图 ,计算曲线下面积。结果　前体脂质体给药后测得的浆膜液吸收曲线下面积大于水溶液给药后测得的曲线下面积。结论　制成前体脂质体可显著增加替加氟的小肠吸收     

In vitro magnesium absorption and the role of intestinal motility.

Magnesium (Mg) is known as an inhibitor of spontaneously contracting muscular tissues. To increase extracellular Mg in vivo, high doses of Mg must be given orally. Therefore, we investigated the effect of different doses of Mg given from the mucosal side of the small intestine of rats. According to the model of Trendelenburg, a system for the perfusion of isolated small intestine was developed, which allows the simultaneous recording of absorption and muscle contractions. Increasing doses of Mg were applied serosally or intraluminally. Intramulinal Mg did not affect intestinal motility. In contrast, increasing concentrations of serosal Mg resulted in a 50% inhibition of motility at 2.9 mmol/l Mg. This indicates no influence on intestinal motility of high doses of Mg acting from the mucosal side. In further studies, the addition of citric acid or taurocholic acid did not alter Mg absorption. Serosally applied amiloride (1 mmol/l) inhibited absorption, but also resulted in complete loss of motility. Since in this model passive diffusion is the most important mechanism of Mg transport, a direct influence of amiloride on Mg absorption can be excluded. From these data, we conclude that intestinal motility influences absorption--also of ions in aqueous solution--and should therefore be taken into account in absorption studies.     

Absorption and metabolic characteristics of p-aminobenzoic acid and its isomer, m-aminobenzoic acid, from the rat small intestine.

Absorption and metabolic characteristics of p-aminobenzoic acid (PABA) and m-aminobenzoic acid (MABA) from the rat small intestine were examined by means of in situ recirculation and in vitro everted sac experiments. p-Aminobenzoic acid was extremely rapidly absorbed from the rat small intestine, whereas the absorption of MABA, the m-isomer of PABA, was comparably slower. This finding was partly explained by the result that PABA is more lipophilic than MABA. The metabolite percentage of PABA was considerably greater than that of MABA in mucosal fluid, tissue, and serosal fluid. On the other hand, a concentration-dependent and a directional difference in the transfer rate of these drugs were observed in everted and noneverted sacs of rat small intestine. Furthermore, mucosal uptake of PABA or MABA was inhibited by 1 mM 2,4-dinitrophenol, 10 mM sodium azide, and pretreatment with HgCl2 (10 mM). These results indicate that MABA, as well as PABA, is transported through the intestine by a carrier-mediated transport system, and that the molecular structure of these drugs is important for their absorption and metabolic characteristics.     

Intestinal metabolism of ethinyloestradiol and paracetamol in vitro: studies using Ussing chambers.

The intestinal mucosal metabolism of ethinyloestradiol (EE2) and paracetamol (P) has been studied in vitro in Ussing chambers. Histologically normal jejunum or ileum was obtained from 19 patients undergoing various resections. The muscularis externa was stripped off the mucosa and the mucosal sheets mounted between two perspex chambers. Tissue viability was routinely assessed by measurement of the transmural potential difference. The percentage of steroid in the serosal chamber, 2 h after addition of EE2 (2 microCi; 80 ng) to the mucosal chamber was 2.3 +/- 0.8% (mean +/- s.d.) which comprised unconjugated drug (0.4 +/- 0.3%), sulphate conjugates (0.7 +/- 0.5%) and glucuronides (0.9 +/- 0.8%). In the mucosal chamber, 56.6 +/- 11.4% was unconjugated steroid, 33.3 +/- 12.4% sulphate conjugates and 2.1 +/- 2.3% glucuronides. Small amounts of the oxidation products 2-hydroxy and 16-hydroxy-EE2 were present. At 2 h, the percentage of paracetamol in the serosal chamber was 3.2 +/- 1.4% (of added P; 2 microCi; 50 ng) of which 0.5 +/- 0.3% was paracetamol sulphate (PS) and 0.1% was paracetamol glucuronide (PG). In the mucosal chamber 2.4 +/- 0.8% and 1.0 +/- 0.2% was present as PS and PG respectively. The total amount of paracetamol conjugated was approximately 4.0%. When paracetamol in the mucosal chamber was increased to 50 micrograms (i.e. by a factor of 1000) there was a decrease in the percentage of added drug metabolized to PS and an increase in formation of PG. The glucuronide:sulphate ratio was increased from 0.34 to 3.56. Competition for sulphation was evident when both paracetamol and EE2 were presented to the intestinal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improvement of intestinal absorption of P-glycoprotein substrate by D-tartaric acid

The purpose of the present experiment was to examine the effects of D-tartaric acid (TA) on intestinal drug absorption under both in situ and in vitro experimental conditions. In the in vitro diffusion chamber experiments, TA (10 mM) added to the mucosal side of rat colon significantly decreased rhodamine123 (Rho 123) transport from the serosal to mucosal side. Since TA has been shown to change the integrity of the epithelial tight junctions in rat colon at low pH conditions, resulting in improved paracellular drug transport, the effect of TA on membrane resistance was examined at pH 7.4 in the present study. It was found that membrane resistance, an indicator of paracellular integrity, did not change at pH 7.4. In the in situ loop method, TA (20 mM) increased the absorption of Rho123 in both ileum and colon but not in jejunum. TA (20 mM) also increased the absorption of daunorubicin in the ileum, but TA (20 mM) did not change the expression level of P-glycoprotein (P-gp). TA (20 mM) significantly inhibited excretion of i.v.-administered Rho123 and daunorubicin into the ileal lumen. In conclusion, for the first time we demonstrated that TA increases the intestinal absorption of P-gp substrates Rho123 and daunorubicin, possibly by modulating the P-gp function without changing the expression level of P-gp in the rat intestine.     

Role of intestinal efflux transporters in the intestinal absorption of methotrexate in rats

The role of intestinal efflux transporters such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs) in intestinal absorption of methotrexate was examined in rats. In everted intestine, the mucosal efflux of methotrexate after application to serosal side was higher in jejunum than ileum, and the efflux in jejunum was suppressed by pantoprazole, a BCRP inhibitor, and probenecid, an MRP inhibitor, but not by verapamil, a P-gp inhibitor. The mucosal methotrexate efflux in ileum was suppressed by pantoprazole, but not by other inhibitors. On the other hand, the serosal efflux of methotrexate after application to mucosal side was greater in ileum than jejunum, and was suppressed by probenecid. In in-vivo rat studies, the intestinal absorption of methotrexate was significantly higher when methotrexate was administered to ileum than jejunum. Pantoprazole increased methotrexate absorption from jejunum and ileum. Probenecid increased the absorption of methotrexate from jejunum but decreased the absorption from ileum, as evaluated by peak plasma methotrexate levels. In conclusion, BCRP and MRPs are involved in the regional difference in absorption of methotrexate along the intestine, depending on their expression sites.     

In vivo intestinal metabolism of 7-ethoxycoumarin in the rat: production and distribution of phase I and II metabolites in the isolated, perfused intestinal loop.

These studies describe the phase I and II metabolism of 7-ethoxycoumarin (7-EC) in the isolated, perfused intestinal loop. Following cytochrome P450-dependent oxidative deethylation of 7-EC by intestinal epithelial cells, the product, 7-hydroxycoumarin (7-HC), undergoes phase II conjugation to form both the glucuronide and sulfate conjugates. The capacity for conjugation of 7-HC within the intestinal epithelium exceeds that of phase I oxidative deethylation, as demonstrated by the absence of increased release of unconjugated 7-HC upon saturation of the conjugation pathways. The formation of both glucuronide (53-62%) and sulfate (41-43%) conjugates contributed to a comparable extent to the overall phase II metabolism of 7-HC within the intestine. This is in contrast to the liver, where sulfate conjugation has been shown to be the predominant phase II metabolic pathway. Furthermore, it was found that unconjugated and sulfate conjugated 7-HC were evenly distributed between the lumenal perfusate and blood compartments, whereas the glucuronide conjugates of 7-HC were preferentially transported at a 4:1 ratio toward the blood. These results indicate that the epithelial cells of the small intestine have the capacity to biotransform orally administered xenobiotics, and the ultimate profile of metabolites generated may influence the biodisposition of these compounds.     

Studies on the in vitro absorption of spice principles--curcumin, capsaicin and piperine in rat intestines.

A comparative evaluation of the absorbability of three structurally similar and physiologically active spice principles in an in vitro system consisting of everted rat intestinal sacs was made. When everted sacs of rat intestines were incubated with 50-1000 microg of curcumin in 10 ml incubation medium, absorption of the spice principle was maximum at 100 microg concentration. The amount of absorbed curcumin present in the serosal fluid was negligible. This and the comparatively lower recovery of the original compound suggested that curcumin to some extent undergoes a modification during absorption. For similar concentrations of added piperine, about 44-63% of piperine disappeared from the mucosal side. Absorption of piperine which was maximum at 800 microg per 10 ml was about 63%. The absolute amounts of piperine absorbed in this in vitro system exceeded the amounts of curcumin. The absorbed piperine could be traced in both the serosal fluid and in the intestinal tissue, indicating that piperine did not undergo any metabolic change during the process of absorption. 7-12% of the absorbed piperine was found in the serosal fluid. When everted sacs of rat intestines were incubated with 10-500 microg of capsaicin, a maximum of 82-88% absorption could be seen in the lower concentrations, and the amount of absorbed capsaicin did not proportionately increase at higher concentrations. A relatively higher percentage of the absorbed capsaicin could be seen in the serosal fluid as compared to curcumin or piperine. When these spice active principles were associated with mixed micelles, their in vitro intestinal absorption was relatively higher. Curcumin absorption in everted intestinal sac increased from 48.7% to 56.1% when the same was present in micelles. In the case of capsaicin and piperine, increase in absorption was 27.8-44.4% and 43.4-57.4%, respectively, when they were present in micelles as compared to its native form.     

Intestinal absorption of rutin in free and conjugated forms.

Quercetin is one of the most common flavonoids in nature, occurring mainly in glycosidic forms such as rutin. Rutin has been reported to exert numerous biochemical and pharmacological activities, though information about its absorption and metabolism is scarce. The aim of this study was to investigate intestinal handling of luminally administered rutin in an isolated preparation of luminally and vascularly perfused rat small intestine. A synthetic perfusate free from blood components was used as vascular medium, with a perfluorocarbon as oxygen carrier. Luminal media consisted of a bicarbonate-buffered sodium chloride solution spiked with rutin (40.5 +/- 1.8 micromol/L). Viability was maintained during the entire perfusion; no differences between rutin and control perfusions for perfusion pressure, lactate-pyruvate ratio, oxygen uptake, and acid-base homeostasis were observed. About 10% of the administered rutin appeared at the vascular side, chiefly as free rutin (5.6%), but some rutin sulfate (2.5%) and glucuronide (2.0%) were also detected. The conjugates were preferentially absorbed to the vascular side, while only traces of the glucuronide (0.2%) were found in the luminal perfusate. Minute amounts of the rutin administered were located in the intestinal tissue (1.1%) in the form of unchanged rutin and its glucuronide and sulfate conjugates. The model used serves as a valuable tool for understanding intestinal handling of the bioactive flavonol glycoside rutin, and the obtained results confirm uptake of rutin in the rat small intestine.