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The indigenous microbiota of healthy animals is known to stimulate intestinal motility. Since the indigenous microbiota of the ileum dominantly contains segmented filamentous bacteria (SFB), we tested the hypothesis that SFB are involved in increasing small intestinal transit (SIT). Five groups of mice were compared: germfree mice, mice mono-associated either with SFB or with Clostridium innocuum , SFB-free mice with a specified pathogen-free (SPF) microbiota and SFB-positive SPF mice. As a measure for intestinal transit, the distance travelled by a charcoal marker was determined 30 min after oral administration. We found a strong increase in SIT in both the mice mono-associated with SFB, and the SFB-positive SPF mice (P

The solubilization of the hydrophilic drugs paracetamol and theophylline, and the lipophilic drugs dantrolene, griseofulvin and ketoconazole has been determined in mixed micellar aqueous dispersions composed of 10 mM taurocholate + 5 mM oleic acid. The solubilization of dantrolene and paracetamol has also been determined in aqueous (mixed) micellar dispersions of 1 g L−1 lysophosphatidyl-choline (LPC), or taurocholate/LPC. The influence of these (mixed) micelles on the absorption of the model drugs from solution was studied in the rat chronically isolated internal loop. Absorption kinetics of the drugs were evaluated on the basis of the disappearance rate of the drug dissolved in the perfusion medium in this loop. Absorption experiments with taurocholate/oleic acid in the perfusate resulted in a reduction of the disappearance rate for the lipophilic drugs and the hydrophilic drug theophylline. This could partly be ascribed to the decreased fraction of drug free in solution as a result of its micellar solubilization for dantrolene, griseofulvin and ketoconazole, but the decrease in the disappearance rate of theophylline was unexpected. Taurocholate/oleic acid, LPC and taurocholate/LPC micelles had no effect on the disappearance of paracetamol. The disappearance rate of dantrolene in the presence of LPC alone was not altered, in spite of the decreased fraction of the drug free in solution owing to its micellar solubilization. In contrast, taurocholate/LPC micelles caused a reduction in the rate of disappearance of dantrolene, as expected according to the phase-separation model. In-vitro, taurocholate and taurocholate/LPC reduced the molecular cohesion of porcine intestinal mucus, whereas LPC alone did not exhibit an effect on the gel structure of mucus. It is concluded that the transfer of solutes across the pre-epithelial aqueous diffusion layer (including the mucus) and the epithelium is unaltered by (mixed) micelles at concentrations in the physiological range.

A method is described to estimate the turnover time of the mucus gel layer in chronically isolated intestinal loops in the rat during perfusion with isotonic saline. Measuring the concentration of a marker substance (total hexose) in the perfusion solution allowed calculation of the volume of produced mucus (Vp) to be in the range between 0.03 and 0.16 μl min−1 cm−1. The volume of the adhering mucus gel layer (Va) was calculated using anatomical data from the literature to be 7.78 ± 0.32 μlcm−1. Hence, the turnover time of the mucus gel layer as given by the quotient of Va/Vp could be estimated to vary in the range between 47 and 270 min. This time scale is well comparable with the mean residence time found for mucoadhesive microspheres in earlier experiments using the same animal model. It is concluded that mucus turnover probably represents a crucial physiological factor for the concept of mucoadhesive dosage forms.

The results in this report show that taurocholate (TC) is able to alter the rheological properties (‘viscosity’) of native porcine mucus in vitro. Below the critical micelle concentration (CMC) the viscosity reduction is dependent on the concentration of TC; above the CMC the viscosity of the mucus is not decreased further: this indicates that the effect of TC on the viscosity of the mucus is not the result of micellar solubilization. The effect of TC on the intralurninal release of mucus components (hexoses) in the small intestine of the rat, is also concentration-dependent: below the CMC (about 8 mM) the hexose output is not altered, but above the CMC the hexose output is increased to a concentration-independent level. The mucolytic agent l -cysteine also reduces the viscosity of mucus in vitro and induces an increase in the hexose output in vivo. Absorption experiments with 10 mM TC in an isolated segment of the small intestine of the rat reveal that the disappearance rate of dantrolene (DA) and ketoconazole (KE) is reduced by TC, but apparently this reduction is almost proportional to the decrease in the fraction of the drug free in solution due to micellar solubilization. DA and KE are not solubilized by l -cysteine and absorption experiments with l -cysteine reveal that the absorption rate of these drugs is not affected by l -cysteine. These results indicate that TC and L-cysteine do not have a measurable or pronounced effect on the absorption barrier in vivo. An explanation for these results may be that, if the rate-limiting barrier to the transport of lipophilic drugs from the lumen to the serosa is located in the mucous layer, then the effects on the mucus by TC and L-cysteine must be neutralized by a compensatory mechanism, which is restoring the barrier function instantaneously, e.g. by the secretion of mucus from the goblet cells.

The influence of sodium taurocholate (TC) on the intestinal absorption of drugs was studied in vivo in a chronically isolated internal loop in the rat. The hydrophilic drugs paracetamol (PA) and theophylline (TP) and the lipophilic drugs griseofulvin (GF) and ketoconazole (KE) were used as model drugs. The drug concentrations were kept below the saturation concentration. Absorption kinetics of the drugs were evaluated on the basis of disappearance rates of the drug from luminal solutions in the intestinal loop. Concentrations of TC above the critical micelle concentration (CMC) did not affect the absorption rate of the hydrophilic drugs PA and TP; the barrier function of the intestinal wall for PA and TP was not altered in the presence of taurocholate. The addition of concentrations of TC above the CMC in the perfusion solution resulted in a reduction of the absorption rate of GF and KE. The reduction in the absorption kinetics of GF in the presence of TC correlated well with the reduction of the drug-free fraction in solution due to micellar solubilization. For KE this relation was less clear. It was not possible to determine, on the basis of the phase-separation model, to what extent the fraction of the drug incorporated in TC micelles contributes to the overall diffusion of GF and KE across the preepithelial diffusion barrier. It was concluded that TC exhibits only a minor, if not negligible, effect on the barrier function of the aqueous diffusion barrier adjacent to the intestinal wall.

Segmented, filamentous bacteria (SFBs) are autochthonous, apathogenic bacteria, occurring in the ileum of mice and rats. Although the application of formal taxonomic criteria is impossible due to the lack of an in vitro technique to culture SFBs, microbes with a similar morphology, found in the intestine of a wide range of vertebrate and invertebrate host species, are considered to be related. SFBs are firmly attached to the epithelial cells of the distal ileal mucosa, their preferential ecological niche being the epithelium covering the Peyer's patches. Electron microscopic studies have demonstrated a considerable morphological diversity of SFBs, which may relate to different stages of a life cycle. Determinants of SFB colonization in vivo are host species, genotypical and phenotypical characteristics of the host, diet composition, environmental stress and antimicrobial drugs. SFBs can survive in vitro incubation, but do not multiply. On the basis of their apathogenic character and intimate relationship with the host, it is suggested that SFBs contribute to development and/or maintenance of host resistance to enteropathogens.

A model is described to study absorption kinetics of drugs in the unanesthetized rat. The surgical technique consists of a long-term isolation of an intestinal segment inside the animal. This isolated loop is used in perfusion experiments. In this model the effects of anesthesia and surgical trauma on absorption kinetics are absent. In addition, this model allows for cross-over experimental schemes. Absorption kinetics can be evaluated on the basis of luminal concentrations or on the basis of blood levels of the perfused drug. In this report, absorption kinetics are evaluated on the basis of steady-state blood levels (Css) of the perfused drug, since the animal can be used in experiments over a long time period. Steady-state blood levels can be used as a measure of the absorption if the compound under investigation shows linear elimination kinetics. Dantrolene sodium was used as a model compound to evaluate this technique. The elimination of dantrolene sodium followed linear kinetics after different intravenous doses in the same rat. The half-life of elimination (t1/2β) of dantrolene sodium was ∼45 min. Perfusions of two different concentrations of dantrolene sodium in the same rat showed that an increase of the perfusate concentration results in a proportional increase in the Css. A prerequisite for performing cross-over experiments is that the absorption characteristics of the isolated segment are constant during the experimental period. This model showed a constant absorption of dantrolene sodium on consecutive days, over a two-week period, in the same rat.

The inclusion of dantrolene sodium, a muscle relaxant with poor water-solubility, inα-,β- andγ-cyclodextrins was determined. Subsequently, the influence of the cyclodextrins on the absorption of the drug from aqueous solutions was investigated in a chronically isolated internal loop in the small intestine of the rat.

The inclusion of dantrolene sodium, a muscle relaxant with poor water-solubility, in α-, β- and γ-cyclodextrin was determined. Subsequently, the influence of the cyclodextrins on the absorption of the drug was investigated in a chronically isolated internal loop in the small intestine of the rat.

The influence of sodium taurocholate (1) on the intestinal absorption of the lipophilic drug dantrolene (2) was studied in vivo in a chronically isolated internal loop in the rat. Concentrations of 2 were kept below the saturation concentration in saline. Absorption kinetics of 2 were evaluated on the basis of steady-state blood levels, which develop during single-pass perfusions, and on the basis of the rate of disappearance of the drug from the perfusate during recirculating perfusions. Compound 1 at a concentration of 10 mM in the perfusate induced a twofold reduction of the absorption rate compared with the same concentration of 2 in saline. Pretreatment of the absorptive surface with a 10 mM solution of 1 had no detectable effect on the absorption rate of 2 in saline. After perfusions with 10 mM solutions of 1, the perfusate concentration of proteins, phosphorus, and hexoses in the effluent was increased. The reduction of the absorption rate can be ascribed mainly to a reduction of the thermodynamically active concentration of 2 as calculated from the phase-separation model. In addition, 10 mM 1 seems to temporarily increase the barrier function of the mucous layer.