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Biomedical subjects

R M Clarke

Publications and source records attributed to R M Clarke.

At least 37 records · Page 2Linked to original sources
PubMed1976

Analysis of the effects of food and of digestive secretions on the small intestine of the rat. 1. Mucosal morphology and epithelial replacement.

A modified Roux-en-Y repositioning of rat small intestine was performed so that the proximal segment of bowel (A) received only bile and pancreastic secretions, the second (B) received food direct from the stomach, and these two segments drained into a third (C). Four to five weeks after operation, cell production was assessed by injection of vincristine into operated, sham-operated and unoperated rats, and counts of blocked metaphases were made on isolated microdissected crypts. Villus height, crypt depth, and the number of crypts per villus (crypt/villus ratio) were also measured. Most of segment A showed no significant differences from sham-operated intestine, although the normal proximo-distal gradient of villus height was abolished. At the distal end (near the anastomosis with segments B and C), crypt depth and cell production were increased. The villus height gradient in segment B was also abolished, although crypt depth and cell production were significantly increased, especially at the proximal end. Crypt/villus ratio was also increased. Segment C showed all the characteristics of small bowel promoted to a more proximal position: increased villus height, crypt depth and cell production. Increased crypt/villus ratio was also observed. These results are discussed in terms of the role of food and of digestive secretions in the control of mucosal morphology and epithelial replacement.

Animals↗
PubMed1975

The effect of intestinal distension and of section thickness on counts of epithelial nuclei in the rat small intestine.

(1) A method is described for counting nuclei in wax-embedded histological sections of epithelium. The counts are independent of section thickness over a wide range (4-10 mum). (2) counts of nuclei were made in villi and crypts of rat small intestine fixed either collapsed or distended by a hydrostatic pressure equivalent to 350 mm of water. There was no significant difference between the counts of nuclei in collapsed or distended gut. (3) Distension reduced the absolute height of villi, and increased their absolute width at the base. (4) The implications of these findings for studies of the morphological basis of intestinal adaptation are discussed.

Animals↗
PubMed1975

Diet, mucosal architecture and epithelial cell production in the small intestine of specified-pathogen-free and conventional rats.

Upper jejunum and terminal ileum were examined in specified-pathogen-free (SPF), conventional and conventional after SPF rearing (ex-SPF) rats. The effect of 2 differential diets on the last 2 groups was examined. Ex-SPF rats had taller villi and deeper crypts than SPF rats, but similar crypt to villus ratios and cell production rates. Ex-SPF rats had similar crypt depth and jejunal villus height to conventional rats on the same diet, but taller ileal villi and a lower cell production rate. Even after 6-8 weeks, in a conventional environment, ex-SPF rat intestine was still not identical with conventional rat intestine. Diet had a significant effect on mucosal architecture, and a smaller effect on cell production rate. It is concluded that diet, microbiological status of colony of origin, and environment after weaning, can all affect mucosal architecture and epithelial cell production, and should be properly controlled in experimental studies.

Animal Feed↗
PubMed1975

The cytological effects of infusion of luminal polyethylene glycol on the rat small intestinal mucosa.

An isolated sac of rat upper small intestine was prepared. Its lower end was drained to the skin. Solutions of known volume and composition were infused into the sac and the intestinal mucosa was examined by light and electron microscopy. Infusion of isosmotic (16.8 percent w/v) polyethylene glycol (PEG) resulted in prompt and progressively severe damage to enterocytes at the top of the villus, while goblet cells and basal-granulated cells were apparently unaffected. Thus, after 6-72 hrs a cap of goblet cells and basal-granulated cells accumulated at the tip of the villus, while the enterocytes underwent vacuolation and disintegration. Infusion of an isosmotic mixture of 1 percent PEG and 5.1 percent glucose caused no damage near the site of infusion, but damaged the intestinal sac further distally...

Animals↗
PubMed1975

The time-course of changes in mucosal architecture and epithelial cell production and cell shedding in the small intestine of the rat fed after fasting.

Rats were starved for 3 days, then either allowed access to food or continued in starvation. The following measurements on the upper jejunum were made on groups of refed and starved rats at nine time intervals after refeeding: villus height, crypt depth, crypt/villus ration, rate of cell production per crypt, and number of epithelial cells shed per villus in 5 minutes. Villus height increased 2 hours after refeeding, while crypt depth changed less dramatically. Crypt/villus ratio was unchanged. The number of shed epithelial cells per villus was reduced below the starved level for 4 hours after refeeding, and did not rise significantly above the starved level until 9 hours; the rate of cell production was not significantly increased until 12 hours after refeeding. No evidence for a reserve of cells in G2 was found, and the 3 hour lag between the rise in cell shedding and the increase in cell production would probably not give enough time for cells in G1 to pass through S and G2. It is concluded that these observations do not support the hypothesis that increased cell shedding from the top of the villus stimulates increased cell production in the crypts of Lieberkuhn.

Animals↗
PubMed1971

Factors influencing the uptake of [ 125 I]polyvinyl pyrrolidone by the intestine of the young rat.

1. The uptake of orally administered [(125)I]polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) by the small intestine of young rats was determined 4 hr after feeding by measurement of the radioactivity remaining in the wall after flushing out the intestinal contents.2. PVP uptake was proportional to the administered dose of PVP for doses of 1 mg and below. At higher doses, uptake was no longer in linear proportion, suggesting a degree of saturation of uptake.3. Litters were reared in one of three environmental temperatures: 13, 20 and 30 degrees C, and were tested to determine the age at which PVP uptake ceased (;closure'). The results were evaluated statistically (see Appendix).4. There was no significant difference between the time of closure in animals reared at 20 and 30 degrees C, but, relative to these groups, closure was significantly delayed, by approximately 48 hr, in animals reared at 13 degrees C.5. Once closure had begun, there were no significant differences in the rate of decline in PVP uptake with age between animals reared at different environmental temperatures.6. Separation of the young rats from their mother both before and after the test-feed of PVP caused a considerable reduction in PVP uptake. Provided that the body temperature of the young rats was maintained, the main factor contributing to the reduction in PVP uptake appeared to be the absence of milk, rather than separation from the mother.

Animals↗
PubMed1970

Structural changes in the small intestine associated with the uptake of polyvinyl pyrrolidone by the young ferret, rabbit, guinea-pig, cat and chicken.

1. The entry of [(125)I]polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) into the epithelial cells of the small intestine has been measured in new-born animals of five species.2. The distribution along the intestine of cells capable of taking up [(125)I]PVP and the decrease and eventual cessation of uptake (closure) with increasing age have been investigated, and have been related to changes in the histological appearance of the small intestine.3. The small intestine of the ferret took up PVP readily until 33-34 days after birth. From 34 to 37 days of age PVP uptake declined sharply and disappeared completely by 40-45 days.4. In the ferret, unlike other species studied, some PVP was taken up by the duodenum. This continued for the first 4 weeks after birth. Thereafter PVP uptake gradually became confined to the terminal ileum.5. In the guinea-pig, PVP uptake was limited to the first 48 hr after birth. During this period the site of uptake was progressively restricted to the terminal ileum.6. In the rabbit, PVP could be taken up in the distal two-thirds of the small intestine for at least 20 days after birth. A decline in uptake occurred between 20 and 22 days after birth in most animals.7. Wide individual variations were seen in the kitten, but PVP uptake was seen in some animals up to 14 days after birth.8. Newly hatched chicks and chicks tested 48 hr after hatching did not take up PVP.9. Histological examination of the small intestine with the light microscope demonstrated that in all species PVP uptake was associated with the presence of vacuoles in the epithelial cells of the villus.10. In the young guinea-pig, large PAS-positive granules were seen in the macrophages of the lamina propria. These appeared to migrate through the epithelium into the intestinal lumen. The significance of this finding and its relation to macromolecular uptake remain unclear.

Age Factors↗