Role of intestinal mucus in the absorption of quinine and water-soluble dyes from the rat small intestine

Absorption of Etoposide (VP-16-213) from the Small Intestine of the Rat. The Potential Role of Mucus as an Absorption Rate Limiting Barrier

The absorption of etoposide (VP-16-213) was investigated in a perfused intestinal loop. The absorbed amount of drug was determined by collecting the blood draining the loop via cannulation of the efferent jejunal vein. The absorption rate of VP-16-213 strongly depended on the composition of the perfusion medium. The addition of taurocholate to an aqueous etoposide solution enhanced the absorption rate. When N-acetylcysteine was added to an aqueous solution, the absorption rate dropped significantly.

Effects of protease inhibitors on the absorption of phenol red and fluorescein isothiocyanate dextrans from the rat intestine

The absorption enhancement effects of three types of protease inhibitors, aprotinin, bacitracin, and soybean trypsin inhibitor, on the small and large intestinal absorption of phenol red (PR) and fluorescein isothiocyanate dextrans (FDs) were examined in rats. Of these protease inhibitors, only bacitracin enhanced the absorption of PR and FDs from the rat small and large intestine. Thus, we suggest that bacitracin has not only a protease-inhibitory but also an absorption-enhancing capability. We examined the effects of various protease inhibitors on intestinal mucosal toxicity by measuring the leakage of Evans blue (EB) from the systemic circulation. Although there was a significant increase in the leakage of EB in the presence of bacitracin, it was considerably less than that in the case of polyoxyethylene 9-lauryl ether (BL-9), which was used as a positive control. Therefore, bacitracin may be a good model adjuvant for improving the intestinal absorption of poorly absorbable drugs because it did not cause serious intestinal mucosal damage, as seen in the case of BL-9.

Rectal absorption enhancement of des-enkephalin-gamma-endorphin (DE gamma E) by medium-chain glycerides and EDTA in conscious rats

The stability of the neuroleptic peptide des-enkephalin-gamma-endorphin (DE gamma E; Org 5878) in the rectal lumen and the rectal bioavailability of DE gamma E were investigated in conscious rats. Furthermore, the influence of peptidase inhibition, peptidase saturation, and absorption enhancement on DE gamma E bioavailability were evaluated. Na2EDTA (0.25%, w/v) prolonged the degradation half-life of DE gamma E in the ligated colon from 33 +/- 7 to 93 +/- 45 min. Without adjuvant, tritium-labeled DE gamma E was absorbed from the rat rectum to a very low extent (0-4%). After administration of an excess of unlabeled DE gamma E or with Na2EDTA, comparable results were obtained. The medium-chain glyceride preparation MGK markedly enhanced the rectal DE gamma E bioavailability, up to 8-20%, which was further increased to 10-44% by coadministration of Na2EDTA. No substantial influence of varying the rectal delivery rate was observed. The results suggest that absorption enhancement and enzyme inhibition both are essential for effective increase of rectal peptide bioavailability.

Effect of systemic anaphylaxis on the absorption of salicylic acid from the rat small intestine

Rats were immunized by intraperitoneal injection of ovalbumin (egg albumin) emulsified in Freund's incomplete adjuvant, and then the effect of an intravenous challenge with ovalbumin on salicylic acid absorption from the small intestine was examined by means of an in situ recirculation technique. The disappearance of salicylic acid from the luminal solution was significantly decreased in rats treated with ovalbumin compared with control groups treated with saline. The decreased absorption of salicylic acid in ovalbumin-immunized rats was related to the anti-ovalbumin antibody responses examined by passive cutaneous anaphylactic reactions. On the other hand, the decreased absorption of salicylic acid was not found in ovalbumin-immunized rats challenged intravenously with bovine gamma-globulin. Similar results were also noted in rats immunized via the footpads with ovalbumin. However, no significant change was observed in the intestinal absorption of salicylic acid in normal (nonimmunized) rats challenged intravenously with ovalbumin. Furthermore, intestinal absorption of sulfadimethoxine and sulfanilamide was significantly decreased during systemic anaphylaxis, whereas no change was observed in the absorption of sulfisoxazole, quinine, sulfanilic acid, and phenolsulfonphthalein. This suggests that the intestinal absorption of rapidly absorbed drugs, including salicylic acid, is more sensitive to systemic anaphylaxis than that of poorly absorbed drugs.

Ion pair absorption of ionized drugs--fact or fiction?

The lipophilicity of some highly ionized drugs at physiological pH is very low. Gastro-intestinal absorption of such compounds cannot be explained by the 'pH-partition' hypothesis. Ion pair formation between a drug and an endogenous counter ion alone resulting in an electrically neutral and potentially more lipophilic species has been proposed as a mechanism to explain the observed, though deficient, absorption of ionic drugs. The concept of ion pair formation between an ionic drug and an exogenous counter ion has been the rationale for attempts to improve penetration of biological membranes and, specifically, result in increased absorption from the gastro-intestinal tract. The validity of the 'ion pair absorption hypothesis' is re-evaluated in the context of a conceptual review of relevant literature.

Clinical aspects of gastrointestinal mucus

In such a bird's eye view of a very complicated and complex literature it is inevitable that significant contributions, particularly from earlier investigators, will have been overlooked. We have tried, however, to provide a reasonable framework for the many presentations and discussions which will take place at this conference. As in the past, it is evident that much needs to be done to reconcile the excellent histochemical studies of gastrointestinal mucus in many diseases with the increasing knowledge of mucin structure and composition. This will only be achieved by extraction of highly pure mucin from diseased bowel. In this regard, post mortem material provides an opportunity for mucin researchers which is not available to workers in other fields because of relative freedom from decomposition. The wedding of mucin technology with immunology is also a major priority. Immunoassay techniques provide the answer to quick and accurate product identification in secretion studies. Specific monoclonal antibodies will provide the route to structural differentiation of antigens in complex mixtures. It is also evident that we must seek to develop a variety of controllable models for the study of functional parameters of mucus in physiological conditions, parasite rejection, neoplasia and inflammatory states. Promising initiatives have been touched upon in this review, but these must only be the beginning. One must conclude, however, by recognizing that advances in knowledge have been truly remarkable since the last conference in 1976. One senses that some of the keys which will one day unlock the gates of this "ill-defined" kingdom are already in hand, while the remainder are at least within reach.

Influence of various anions on intestinal disappearance of hexamethonium chloride and pralidoxime chloride in rats

The intestinal transfer of two poorly absorbed quaternary ammonium drugs, hexamethonium chloride (I) and pralidoxime chloride (II), in the presence of various organic and inorganic anions was investigated in the rat using a modified in situ gut technique. The results were in agreement with those of the conventional in situ loop and plasms drug level techniques. Of the anions investigated, cholate, desoxycholate, taurocholate, phoscholate, dehydrocholate, and hyodesoxycholate had the greatest effect on increasing the amount and rate of disappearance of I. Similarly, the amount and rate of disappearance of II were enhanced markedly in the presence of phoscholate and trichloroacetate. The effect of cholate and phoscholate was investigated in detail. The membrane permeability and histological studies indicated that these anions may compromise the structural integrity of the membrane tissue, thus enhancing drug transfer.