Hydrogen bond formation as basis for radical scavenging activity: a structure-activity study of C-methylated dihydrochalcones from Myrica gale and structurally related acetophenones.

A naturally occurring flavonoid, myrigalone B (2',6' -dihydroxy-4'-methoxy-3',5'-dimethyl-dihydrochal-cone) is an effective antioxidant and scavenger of the diphenylpicrylhydrazyl radical, while the closely related angoletin (2',4'-dihydroxy-6'-methoxy-3',5'-dimethyl-dihydrochalcone) is inactive. From NMR spectra, it appears that myrigalone B has a time-averaged conformation in which the substituted aromatic ring is orthogonal to the carbonyl group, while angoletin is coplanar. By donating a phenolic hydrogen in radical scavenging, myrigalone B will lose its symmetrical structure and may thereby change to a coplanar conformation forming a strong intramolecular hydrogen bond between the remaining phenolic hydrogen and the carbonyl group. The energy gain entailed would then appear to be a driving force for the radical scavenging by myrigalone B. Angoletin, being coplanar, lacks this driving force. To verify this hypothesis, the conformation and radical scavenging activity of a series of phenolic acetophenones were studied. All substances that had an orthogonal conformation and could form intramolecular hydrogen bonds by loss of a phenolic hydrogen were DPPH scavengers, while compounds lacking these properties were inactive. From this, we propose that formation of intramolecular hydrogen bonds may lead to radical scavenging activity.

Compartmentation of intestinal drug sulphoconjugation. Incorporation of luminal and contraluminal [35S]sulphate into 1-naphthol by the isolated mucosa of guinea pig jejunum and colon.

Compartmentation of 1-naphthol metabolism was inferred from the metabolite pattern and distribution in the isolated mucosa of guinea pig intestine mounted in a flux chamber (Sund and Lauterbach, Arch Pharmacol Toxicol 58: 74-83, 1986). To verify the existence of these compartments the dependence of [35S]sulphate incorporation into 1-naphthol sulphate on the side of administration of 1-naphthol and [35S]sulphate was determined. Isolated mucosae were pre-equilibrated with [35S]-sulphate (5 x 10(6) cpm/mumol, 1 mM) for 30 min and subsequently incubated for 15 min with 50 microM 1-naphthol. The three 1-naphthol sulphate fractions (luminal side, blood side and tissue) were assayed by HPLC and liquid scintillation counting; their specific activity was calculated as percentage of the specific activity of the inorganic sulphate administered. 1-Naphthol glucuronide was also measured. In jejunal experiments: after luminal administration of 1-naphthol, 1-naphthol sulphate appeared almost exclusively in the luminal solution; its specific activity approached 70% and 3%, when [35S]sulphate was added to the luminal and blood side, respectively. After introducing 1-naphthol and [35S]sulphate on the blood side, a high and similar specific activity of 50-60% was observed in all three 1-naphthol sulphate fractions (luminal and blood side, tissue) though adding [35S]sulphate to the lumen side decreased the specific activity to 10-20%. In experiments on colonic mucosa: a specific activity both of luminal and blood side 1-naphthol sulphate of more than 50% was observed with blood side [35S]sulphate irrespective of the side of 1-naphthol administration. When [35S]sulphate was placed on the luminal side the specific activity of blood side 1-naphthol sulphate dropped to only 3%, and that of luminal 1-naphthol sulphate ranged between 6% and 20%. Supplementary experiments in which mucosae were exposed to 1-naphthol and [35S]sulphate for 45 min without preincubation showed a tendency to decrease the lumen: blood distribution ratio of 1-naphthol sulphate. However, the general pattern of 1-naphthol sulphate specific activity remained unchanged. The experiments provide further evidence that the jejunal conjugation of phenolic drugs is being performed in two major compartments, which are accessible from the lumen ("luminal compartment") and blood ("systemic compartment") side. The luminal compartment seems practically inaccessible to blood side sulphate as is the systemic compartment for luminal 1-naphthol. In the colonic mucosa, a major "systemic compartment" receiving its sulphate from the blood side is the site for most of the events, but a minor "luminal compartment" seems to be involved as well.

Inhibition of lipid peroxidation in low-density lipoprotein by the flavonoid myrigalone B and ascorbic acid.

Lipid peroxidation in human LDL (0.05 mg protein/mL) incubated with Cu(2+)-ions (5 microM) in vitro was dose-dependently inhibited by the flavonoid myrigalone B (MyB) and by ascorbic acid. MyB at 6 microM increased the oxidation lag time by 135 +/- 24 min (approximately 5-fold compared to controls) and reduced the maximum oxidation rate by 46 +/- 5%. Ascorbic acid, at 9 microM, increased the lag time by 179 +/- 29 min (6-fold compared to controls) but did not affect the maximum oxidation rate. The increase in lag time induced by MyB was enhanced in the presence of ascorbic acid. Their effects were additive, except when both were present at the highest concentration tested, when a significant potentiation, giving an increase in lag time of approximately 2 hr more than the sum of separate effects, occurred. Concentration-time curves for MyB in the absence and presence of ascorbic acid showed that the vitamin protected MyB against deterioration during incubation, and indicated that the net consumption of MyB in the oxidation process was reduced. No differences were observed when ordinary ascorbic acid and Ester-C, a commercial vitamin C product, were compared. In conclusion, MyB and ascorbic acid seem to interact in a way that further improves the antioxidant status of the LDL particle relative to each substance separately.

Enzyme changes in remodelling epithelial cells: a histochemical study of the rat jejunum in vivo during and following exposure to deoxycholic acid.

Loops of rat jejunum were exposed in vivo to different concentrations of deoxycholic acid (DOC; 0, 2.5, 5, 10 and 20 mM). Following a 30 min exposure period, DOC was washed out of the loops and the intestines were allowed to recover for 15 or 150 min. Frozen tissue for enzyme histochemistry was collected during exposure and following the recovery periods. As shown previously, exposure to DOC caused a dose-dependent loss of epithelial cells at the villous tips and denudation of the lamina propria. Flattened epithelial cells bordering the denuded areas were, however, responsible for a rapid restoration of epithelial continuity, which was completed within 15 min. In the present study, these flattened cells showed normal reactivity for non-specific esterase and succinate dehydrogenase. In contrast, following a prolonged recovery period (150 min), a subpopulation of enterocytes at the villous tips that otherwise appeared normal showed decreased reactivity for brush border enzymes and non-specific esterase, and a positive reaction for mucin. A shutdown in the synthesis of cytoplasmic enzymes and redistribution of cell surface enzymes could be responsible for these late occurring enzyme changes, that were consistently observed after 150 min of recovery from DOC at 20 mM. Alternatively, retention of goblet cells and/or a modification in enzyme synthesis may explain the presence of mucin that was demonstrated in the epithelial cells which had low enzyme reactivity.

Alterations of ultrastructure and of cytoplasmic filaments in remodelling rat jejunal epithelial cells during recovery from deoxycholate.

Structural features associated with reversibility of lesions induced by deoxycholic acid (DOC) were studied by electron microscopy and immunofluorescence techniques. Tied jejunal loops were incubated in vivo with 2.5-20 mmol/l DOC in isotonic solution. Immediately after this treatment, or after a recovery period of 15 or 150 minutes following washout of the bile acid, the loops were excised and processed. DOC produced epithelial lesions whose severity and reversibility were concentration-dependent. Ultrastructural features associated with the reversibility of the lesions were particularly apparent in specimens exposed to 10-20 mmol/l DOC. These features included cell flattening with the formation of thin, veil-like structures into the eroded area by cells at the edges of the erosions. Immunofluorescence studies showed a redistribution of actin and cytokeratin filaments to the margins and leading edges of the flattened cells. It is suggested that cell flattening and migration are responsible for the rapid morphological recovery of the injured epithelium. Actin and cytokeratin appear to be instrumental in the remodelling and migration.

Morphological and functional recovery following exposure to deoxycholic acid. A study in the rat small intestine in vivo.

Whereas many studies deal with teh deleterious effects of unconjugated deoxycholic acid on epithelial morphology, few are concerned with the reversibility of these effects, the subject of the present study. Tied jejunal loops in the rat were incubated for 30 minutes with deoxycholic acid (2.5-20 mmol/litre) in isotonic solution. Immediately after this treatment, or after a subsequent recovery period of 15 or 150 minutes following wash out of the bile acid, the loops were excised, fixed and examined by light microscopy and scanning electron microscopy. Deoxycholic acid produced epithelial lesions whose severity and reversibility depended on the concentration applied. However, even the severely affected epithelium obtained by treatment at 10-20 mmol/litre was reverted to normal within 150 minutes, and a substantial normalisation was observed already after 15 minutes. An exception to this rapid restoration of epithelial morphology and integrity was noted in villi which had suffered necrosis of lamina propria. The revertion of epithelial pathology was paralleled with a normalisation of glucose absorption, of the potassium ion and protein content of the loop fluid, and of the paracellular epithelial permeability as measured with 3-H-poly-ethylenglycol. Morphometry showed that deoxycholic acid caused villous atrophy without affectin the crypt length. The extent and reversibility of this atrophy depended on dose and recovery time as above. It is suggested that the remarkably fast morphological restitution proceeds mainly by process involving cellular remodelling and migration.

Plasma ascorbic acid concentrations in healthy dogs.

Using a highly sensitive and selective analytical method and careful stability control, plasma concentrations of ascorbic acid were determined in German Shepherd Dogs, Labrador Retrievers and Siberian Huskies, a total 99 animals. Mean concentration was 35.9 micromol l(-1)(range 18.2-50.7), and no significant variation was observed neither between breeds nor between females and males. These and previous reported data on plasma ascorbic acid levels in dogs are discussed in the light of methodological aspects.

Pharmacokinetics in dogs after oral administration of two different forms of ascorbic acid.

The dog is able to synthesise ascorbic acid (AA), but is frequently given the vitamin in an attempt to improve health and performance. The pharmacokinetics of AA in this species, however, are not well studied. Using a selective analytical method and careful stability control, the pharmacokinetics of orally given AA was studied in 20 dogs, at two dosage levels (15 and 50 mg kg(-1)) and with two forms of supplement [crystalline AA and the vitamin C product Ester-C(Inter-Cal Corp., Prescott, AZ, USA)]. After oral administration, a rapid increase was found in the plasma level of AA, indicating a possible intestinal active transport mechanism in this species. The obtained C(max)and AUC values were found to increase in a non-linear fashion when the dose of AA was increased. The pharmacokinetic modeling of the elimination of AA was made difficult by a pronounced secondary peak appearing after about 9 hours. The comparison of crystalline AA and Ester-C did not indicate any significant differences in pharmacokinetic parameters between the two preparations of the vitamin.

Studies on laxatives: biliary and urinary excretion in rats given danthron by intravenous infusion or gastric intubation.

Rats were infused with danthron (I) at doses of 0.48, 2.2 and 5.8 mumol/100 g body weight, or given 12 mumol/100 g with gastric tube. TLC of bile and urine demonstrated a number of metabolites, at both administration routes. These included I monosulphate (II) and -glucuronide (III), two other phase 2 metabolites which behaved as the corresponding diconjugates, and several phase 1 metabolites (IV) in conjugated form. IV as a group were estimated by photometry of hydrolysed samples, using I as a reference. Danthron conjugates as a group were determined in such samples by a specific method for I. Moreover, II and III were determined individually in unhydrolysed specimens. Following infusion, about 80% of the danthron conjugates in bile were excreted after 1 hour; the dose fractions found after 5 hours represented about 20%, 30%, and 40% at the low, intermediate and high dose level, respectively. The corresponding fractions in urine were 16%, 12% and 10%, giving rise to bile:urine excretion ratios of 1.3, 2.7 and 4.0, respectively. This change in excretion pattern was associated with changes in metabolite muster, which involved a decrease in the balance of IV:I conjugates, as well as an increase in III:II ratio. IV was more abundantly present in bile than in urine, and showed a more sustained excretion than the I conjugates. By intragastric administration, the cumulated excretion (bile + urine) of I conjugates were only 6%, 8% and 5% of dose, in three consecutive 6 hours' periods (0-6, 6-12 and 12-18 hours after dosing). The bile:urine excretion ratios seemed to decrease with time, as did the III:II ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose and cation transport in rat jejunum, ileum and colon in vivo: control experiments, and effect of cationic surfactant.

Osmotically balanced solutions of glucose (0.5-300 mM) and sodium chloride, containing cetrimonium bromide (cetrimide, 0.8-4.1 mM), were instilled into the jejunum, ileum and colon of anaesthetized rats. Net transport of glucose, sodium and potassium was studied by their disappearance from, or accumulation into the intestinal lumen during 15 min incubation. Cetrimide caused the following shifts in normal jejunal and ileal glucose absorption: At low luminal glucose levels, absorption was strongly depressed and may be converted to net secretion. At intermediate levels, inhibition was less pronounced, and at high luminal glucose levels absorption was enhanced. Similar changes were seen in the colon. Furthermore, cetrimide caused a three-fold change in the regression lines relating net sodium fluxes to the initial sodium concentration: The lines became steeper, the correlation was improved and the sodium concentration value corresponding to zero net transport was elevated. Net potassium secretion was increased. These changes are all consistent with the view that surfactants cause an increase in passive permeability. Quantitatively, the effect of cetrimide increased with localization in the order colon greater than ileum greater than jejunum. Benzalkonium chloride (0.5-1.7 mM) was tested in the ileum only, and caused quite similar effects.

Anthraquinone laxatives: metabolism and transport of danthron and rhein in the rat small and large intestine in vitro.

A previous in vitro study by Sund and Hillestad in 1982 showed that dihydroxy-diphenylmethane laxatives undergo intestinal metabolism, and suggested a regionally dependent transport asymmetry of gut glucuronides. The present study was initiated since such experiments on anthraquinone diphenols are lacking. Everted sacs of rat jejunum and stripped colon were filled with Krebs-Henseleit solution (K-H) on the serosal (BL) side, and bathed at the mucosal (LU) side with K-H containing either danthron (3-4 nmol/ml) or rhein (10 nmol/ml). After 60 min incubation at 37 degrees C, LU and BL solutions and gut tissue were analysed for parent diphenol and metabolites by reverse-phase high-pressure liquid chromatography. Reference metabolites were isolated and purified from urine and bile of rats infused with danthron or rhein. The studies showed: (1) only small amounts of unchanged drug were present on the contraluminal side; (2) in both tissues, danthron was transformed into its monoglucuronide (G) and monosulphate (S); the ratio G:S was 6-8:1 in jejunum, and even greater in colon; (3) in jejunum, G and S were mainly secreted (LU:BL distribution ratios greater than 10:1); (4) in the colon, however, the main G fraction was absorbed (BL:LU ratios of 3:1), whereas a slight net secretion of S seemed to take place; (5) residuals (%) in gut tissue were small; (6) rhein was more slowly taken up and metabolized, but seemed otherwise to behave as danthron. The results are in principle similar to those obtained by indirect conjugate assay in the study on diphenylmethanes.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Naphthol metabolism and metabolite transport in the small and large intestine. II: Effect of sulphate and phosphate ion omission, and of 2,6-dichloro-4-nitrophenol in the isolated guinea pig mucosa.

A previous study (Sund & Lauterbach 1986) in the isolated guinea pig mucosa showed a complex pattern of 1-naphthol (I) metabolism and metabolite (glucuronide = II and sulphate = III) transport in relation to tissue studied (jejunum and colon) and administration side (lumen versus blood side). In the present paper aspects of I metabolism and II and III transport have been further studied. The experiments involved: Omission of inorganic sulphate in the incubation solution at one particular side or at both sides, to see if and how intestinal sulphoconjugation depended on side of sulphate ion entry, and if II and III efflux might be linked to sulphate ion influx. Similar omission experiments with inorganic phosphate, and Incubation in presence of 2,6-dichloro-4-nitrophenol (IV), a drug claimed to be a selective inhibitor of sulphoconjugation. The experiments showed: In the jejunum, sulphate ion caused a much stronger stimulation of III formation from the lumen than from the blood side, when I was added at the luminal side. In the colon, however, the sulphate ion was more effective on the blood side than on the lumen side, regardless of side at which I was added. More experiments are needed to clarify if conjugate efflux is affected by sulphate ion omission as well. Omission of inorganic phosphate did neither affect I metabolism nor II and III efflux. IV (present at both sides at once) had complex effects, involving inhibition of II and III synthesis as well as their efflux, and, in part, a change in their normal lumen: blood distribution pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug metabolism and metabolite transport in the small and large intestine: experiments with 1-naphthol and phenolphthalein by luminal and contraluminal administration in the isolated guinea pig mucosa.

The metabolism and metabolite transport of the monophenol 1-naphthol (I) and the diphenol phenolphthalein (II) have been studied in a symmetrical setup of the isolated jejunal and colonic mucosa from the guinea pig (Lauterbach 1977). In both tissues, the main metabolites of I were its sulphoconjugate and glucuronide, but the rate of metabolism, relative proportion of the metabolites and their distribution pattern varied with tissue and drug administration side in the following manner: By luminal administration (50 nmol/ml) in the jejunum, the metabolism was nearly complete within 45 min., more sulphate (1.5-3x) than glucuronide was formed, and both metabolites were predominantly transferred back to the lumen. By blood-side administration, the metabolism was less complete due to a significant decrease of the sulphated fraction. In consequence, more glucuronide (1.5-3x) than sulphate was formed. Moreover, the efflux pattern of the metabolites changed completely; the greater part of the glucuronide fraction now being conveyed to the blood side, whereas the sulphate tended to distribute in a 1:1 fashion on the lumen and blood side. The colonic mucosa behaved in a dissimilar way, since neither I metabolism nor metabolite efflux pattern in this tissue was influenced significantly by drug administration side. More sulphate (1.5-3x) than glucuronide was formed by both routes, and the metabolite distribution was similar to that observed by blood side administration in the jejunum. The changes described above were associated with changes in tissue accumulation of free I and metabolites; accumulation of I by luminal administration in jejunum was insignificant and that of the metabolites small. The main change caused by a higher concentration of I (130 nmol/ml) was a decrease in the sulphated fraction in the colon. II was metabolized at a slower rate than I, and a significant tissue accumulation of free II was observed in all instances. The monoglucuronide was the main metabolite. Only minor amounts of II monosulphate were formed, making its distribution pattern difficult to ascertain. The distribution of II monoglucuronide on the other hand was generally similar to that described for its I analogue.

Glucose and cation transport in rat jejunum, ileum and colon in vivo: effects of anionic and nonionic surfactants, and of desoxycholate.

Osmotically balanced solutions of glucose (0.5--300 mM) and sodium chloride, containing surfactants, were instilled into the small or large intestine of anaesthetized rats. Net absorption or secretion of glucose, sodium and potassium was studied. The surfactants tested were dodecylsulphate (3.4--17 mM), dioctylsulphosuccinate (1.8--11 m/M), Lubrol WX (0.1--5%), Triton X 100 (0.25%) and desoxycholate (2.5 mM). Qualitatively, the results were similar to those obtained previously with cationic compounds, suggesting a common mode of action for all surfactants studied. 17 mM dodecylsulphate seemed to abolish completely physiological glucose transport in the jejunum and ileum. At a lower concentration, and witth the other surfactants, normal glucose transport was affected to an intermediate extent.

Uptake, conjugation and transport of laxative diphenols by everted sacs of the rat jejunum and stripped colon.

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 greater than DES greater than 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 (greater than or equal to 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.

Studies on hydragogue drugs: effect of surfactants on cAMP levels in the rat jejunal mucosa in short time experiments in vivo.

Theophylline and the surface active agents specified below were instilled into the jejunum of anaesthetized rats, and the cAMP levels in the mucosal tissue determined after 71/2 and 15 min. incubation in vivo. Most experiments were done in rats prepared with two tied intestinal loops; one of these served as the control loop and the other as the stimulated loop. The surfactants (mmol/l) included dodecylsulphate (17), dioctylsulphosuccinate (5.6), cetrimonium bromide (4.1), deoxycholic acid (2.4 and 3.6) and Lubrol WX (0.5% w/v). Theophylline (10 mmol/l) caused a substantial increase in cAMP (110% +/- 17, n = 7 and 60% +/- 8.9, n = 10, respectively) and dodecylsulphate a minor and transitory increase (28.1% +/- 3.8, n = 10 and 11.7% +/- 4.9, n = 8). The other agents were without stimulatory effect on cAMP, although like dodecylsulphate they may significantly affect normal intestinal cation and glucose transport under these conditions. The results, therefore, do not suggest that stimulation of cAMP and intestinal secretion induced thereby is any significant phenomenon in the overall hydragogue effect of these agents, at least not in short term jejunal experiments.

Intestinal secretion of sulphanilic acid by the isolated mucosa of guinea pig jejunum.

Tissue uptake and transepithelial permeation of 35S-sulphanilic acid were studied in the isolated guinea pig jejunal mucosa. Methoxy-3H-inulin added simultaneously served as a marker for the extracellular space and permeability of paracellular shunt pathways in the preparation. The uptake of sulphanilic acid from the blood side exceeded that from the luminal side 4--7 fold. The permeation of the acid was strongly correlated to the permeation of inulin. At 5 micrometer and 2.5 mM sulphanilic acid under aerobic conditions, the regression lines for the permeation from lumen to blood pass almost through the origin, while the regression lines for the permeation from blood to lumen intersect the ordinate at a positive Y-value. In anaerobiosis, at 25 mM sulphanilic acid, or with addition of p-toluene sulphonic acid only one regression line is obtained for the permeation in both directions. It is concluded that besides a permeation of sulphanilic acid across inulinpermeable shunt pathways an active transport system exists, which transfers the acid from the blood to the luminal side. This system is saturable, depends on aerobic energy and exhibits mutual inhibition by a structurally related compound. The results are comparable to those previously obtained with cardiac glycosides and quaternary ammonium compounds, in the same preparation. Thus, the intestinal mucosa is able to secrete the same classes of compounds which are secreted by the liver and the kidney.

In vivo reversibility of the jejunal glucose and cation transport alteration caused by intraluminal surfactants in the rat.

Tied jejunal loops in anaesthetized rats were under standardized conditions pre-exposed for 30 min. with Tyrode solution containing surfactants. 5, 20 or 150 min. after wash out of bulk surfactant, the loops were re-instilled with Tyrode containing glucose at 5--15 mmol/l. Net glucose, sodium and potassium transport were studied for 15 min. by changes in intraluminal amounts, and compared with results obtained in control rats. The surfactants (mmol/l) tested were the anionics dioctylsulphosuccinate (5.6) and dodecylsulphate (8.5--17), the cationics cetrimonium bromide (2.1--4.1) and benzalkonium chloride (2.1), the nonionics Triton X100 (0.25%) and Lubrol WX (0.25--0.5%) plus cholic acid (4.9) and desoxycholic acid (1.3--2.5). In most cases, the glucose transport was normal or fairly normal after 150 min., most of the restoration taking place shortly after surfactant removal. However, Lubrol in particular caused more irreversible effects. Generally, the changes in net cation transport tended to be less easily reversible than the alteration in glucose transport. In so far as a normal or near to normal glucose transport is unlikely to occur unless both functional and structural integrity of the epithelium is preserved, the results indicate that in most cases there is but insignificant epithelial damage under the experimental conditions. Since, furthermore, these surfactants can interact with glucose transport in the same technique even at lower concentration and shorter incubation time than used here, it is concluded that the interaction of surfactants with intestinal transport is not neccessarily linked to gross histo-pathological changes.

2-Naphthol metabolism and metabolite transport in the isolated guinea pig mucosa: further evidence for compartmentation of intestinal drug metabolism.

As an extension of a previous study on the metabolism of 14C-1-naphthol (1-N) by the isolated guinea pig mucosa (Sund & Lauterbach 1986), the isomeric compound 2-naphthol (2-N, 50-130 nmol/ml) has now been examined. 14C-Labelled drug was added to the luminal or contraluminal fluid bathing the two sides of jejunal or colonic mucosal sheets in a symmetrical set up. After aerobic incubation for 45 min. at 37 degrees, the fluid compartments and the tissue were analysed for parent drug and metabolites. Like 1-N 2-N was transformed into its sulphate and glucuronide. In the jejunum, 2-N was more extensively sulphated than 1-N, whereas in the colon the metabolite profiles (sulphate:glucuronide ratio) of the two isomers were similar. Generally, the metabolism rate of 2-N, its metabolite profile and metabolite transport pattern (lumen: blood distribution ratio) as well as the tissue accumulation of parent drug and metabolites, depended on the side of drug administration and on the tissue studied. Thus, changing the drug administration had a pronounced impact on the jejunal metabolism and transport, but caused only minor effects in the colon. In summary, this study emphasizes that drug metabolism and metabolite transport differ in the small and large intestine. The data further support the hypothesis that jejunal drug metabolism takes place in two compartments, of which the most active one is accessible from the lumen side and the other from the blood side. The possibility that colonic drug metabolism may also involve compartmentation should be considered although the present study provided very little evidence for this.

A note on the complex metabolism of danthron infused into the rat.

Danthron infused intravenously in rats shows a complex dose-dependent pattern of metabolism and excretion. The metabolites, particularly the more polar ones, are in general excreted predominantly in bile, to a lesser extent in urine. They can be separated as metabolite groups according to polarity and molecular size on a Sephadex LH 20 column. The present paper describes a further study within a bile-derived metabolite group, which proved to be particularly heterogeneous. It contained more than a dozen metabolites, which were conjugates of four different aglycons including the parent danthron. 1H NMR spectral data for danthron monosulfate and monoglucuronide are also presented.