Materials in the Colon

Our early scintigraphic studies, in which Tc-99m pellets and In-111 labeled non-disintegrating tables were dosed together, suggested differential transit through the lower gut (9). This was confirmed in later studies in which small tablets and 

The anatomy of the distal colon, with its thick muscular walls, suggests a predominantly propulsive activity. Studies with single administrations of pellets or Pulsincap devices suggested that the distal part of the transverse colon area is difficult to treat since this area and the descending colon function as a conduit. Steady-state measurements confirm this assertion (48) and Weitschies group have also reported data showing mass movements propel objects quickly through the distal transverse colon. 

In order to look at the probable duration of treatment with topical agents for colonic drug delivery, we have conducted studies with normal subjects and patients with left-sided colitis. The subjects and patients were dosed daily with indium-Ill-labeled amberlite resin and imaged throughout the day. On the fourth, the division of activity in the colon was 67% in the proximal half and 33% in the distal half day for the control subjects, whereas for the patients with colitis the distribution was 90 10. These data emphasize the problem of treating left-sided colitis effectively during active periods of disease. 

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Epidemiological studies have indicated that dietary fiber is a contributing factor in lowering the incidence of cancer of the colon. Colon cancer is the leading cause of cancer death in the United States. The increase in the bulk of material in the colon provided by insoluble fibers has been speculated to reduce the concentration of chemicals in the colon that promote the conversion of a normal colonocyte to a cancerous one. An increase in flow rate through the colon, generated by dietary fibers, would reduce the time of exposure of the colonocytes to these chemicals. These effects should reduce the levels of cancer-producing chemicals supplied directly by the diet, as well as those produced by microbial metabolism. Further details are revealed in the Diet and Cancer chapter. 

With XA1PcS3, selective photonecrosis of colonic tumors induced with dimethylhydrazine was observed with low drug doses (0.5 mg kg-1), but selectivity over normal tissue disappeared at 5 mg kg-1.329 The use of this material (in the form of PHOTOSENS as a mixture of di- and tri-sulfonic acids (7)) in extensive clinical treatments in Moscow has been referred to in Section 9.22.4. 

Dispersion of material following timed release in the colon using Pulsincap devices. Mean s.d. 

In the colon, semifluid material entering from the small bowel is thickened by absorption of water and salts (from about 1000 to 150 mL/d). If, due to the action of an irritant purgative, the colon empties prematurely, an enteral loss of NaCl, KCl and water will be incurred. To forestall depletion of NaCl and water, the body responds with an increased release of aldosterone (p. Ltillmann, Color Atlas of Pharmacology... 

A mass movement is characterized by the following sequence of events. First, a constrictive ring occurs at a distended or irritated point in the colon, usually in the transverse colon, and then rapidly thereafter the 20 cm or more of colon distal to the constriction contract almost as a unit, forcing the fecal material in this segment en masse down the colon. During this process, the haustrations disappear completely. The initiation of contraction is complete in about 30 sec, and relaxation then occurs during the next 2 to 3 min before another mass movement occurs. But the whole series of mass movements will usually persist for only 10 min to half an hour, and they will then return perhaps a half day or even a day later. 

The gastrocolic reflex stimulates motility in the colon during or just after eating, when chyme enters the colon from the ileum. The content of the distal colon may be stored there for variable periods until defecation occurs, which may be 24 hours or more after eating. The rectum is normally empty and movement of faecal material into the sigmoid colon and rectum stimulates the defecation reflex. 

The rise in the production and use of synthetic polymers worldwide was recently estimated at around 140 million tonnes per year, with most of these being petroleum-based and causing an increasing problem both as environmental pollutants and in the pressure they exert as landfill components. Biodegradation and biodeterioration of these materials can play an important role in microbial ecology and nutrient cycling in the environment. Compared to the importance of these materials in the environment, there have been relatively few studies on the colonization. 

The digestibility of starch depends on source, physical condition, and food preparation. With the exception of lignin, dietary fibers may be partially or fully hydrolyzed by enzymes of the microflora present In the colon, iJome products arc absorbed into the bloodstream, but most serve as energy sources for the colono-cy tes. Specific dietary fibers can influence fecal bulk, the rate of passage of material through the intestines, and certain maladies such as constipation. 

Gazzaniga, A. Busetti, C. Moro, L. Crimella, T. Sangalli, M.E. Giordano, F. Evaluation of low viscosity HPMC as retarding coating material in the preparation of a time-based oral colon specific delivery system. Proceed. Int. Symp. Control. Rel. Bioact. Mater., 1995 Controlled Release Society Minneapolis, MN, 1995 242. 

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