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R M Clarke

Publications and source records attributed to R M Clarke.

41 records · Page 3Linked to original sources
PubMed1970

A new method of measuring the rate of shedding of epithelial cells from the intestinal villus of the rat.

Epithelial cells shed from the intestinal villus in starved rats were trapped in mucus which the goblet cells were stimulated to secrete; the number of trapped cells per villus was counted in whole mounts of fixed Feulgen-stained specimens from three sites in the small intestine. Increase in the interval between stimulation and fixation caused an increase in the number of shed cells per villus; the rate of this increase was postulated to represent the rate of cell shedding. The rate of cell production per crypt was measured with Colcemid; this rate, multiplied by the number of crypts per villus, gave the rate of cell production per villus. There was good agreement between these estimates of cell production and cell shedding.

Animals↗
PubMed1969

The use of [125-I] polyvinyl pyrrolidone K. 60 in the quantitative assessment of the uptake of macromolecular substances by the intestine of the young rat.

1. A method has been developed which allows the quantitative estimation of the uptake of labelled polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) by the wall of the small intestine of young rats.2. Four hours after feeding a standard dose of [(125)I]PVP by stomach tube, the small intestine was thoroughly washed out, and the radioactivity of the intestinal wall measured. Under these conditions, the small intestine of animals less than 18 days old took up more than 50% of the radioactivity which had left the stomach. There was no increase in PVP uptake if the duration of absorption exceeded 4 hr. The PVP was taken up by the epithelial cells of the villus, and its intracellular localization has been demonstrated by fluorescence microscopy and can be related to vacuolation in the cells.3. In animals between 18 and 20 days old the uptake of PVP declined progressively, until, in animals more than 20 days old, less than 5% of the radioactivity was taken up by the intestinal wall.4. There is good agreement between the reported age of termination of antibody absorption in young rats and the age at which PVP uptake ceased in the present experiments. It is suggested that the loss of ability of the intestine to take up substances of high mol. wt. may be the factor which limits the duration of the period of antibody absorption in this species.

Animals↗
PubMed1969

An analysis of the mechanism of cessation of uptake of macromolecular substances by the intestine of the young rat ('closure').

1. The longitudinal distribution of cells capable of absorbing macro-molecular material has been determined in the small intestine of the young rat by measurements of the uptake of [(125)I]polyvinyl pyrrolidone (PVP).2. PVP uptake was never seen in the duodenum and became restricted to the distal half of the small intestine by the 18th day of life. The subsequent decline to zero in PVP uptake was due to an almost uniform decrease in PVP uptake by the distal half of the small intestine.3. Histological studies indicate that this rapid decline in PVP uptake did not reflect a decrease in uptake by individual cells, but rather their replacement by new cells incapable of taking up PVP.4. Autoradiographic estimates of turnover time in the intestinal epithelium using tritiated thymidine reveal good agreement between the time needed to replace completely the epithelium of the ileum (62 hr) and the duration of the rapid decline in PVP uptake (approximately 3 days).5. It is concluded that on or about the 18th post-natal day there is an abrupt change in the functional characteristics of the apical plasma membrane of cells produced by the crypts of Lieberkühn in the distal half of the small intestine. The stimulus for this change is unknown, but cells produced subsequently cannot take up PVP.

Age Factors↗