The measurement of villus cell population size in the mouse small intestine in normal and abnormal states: a comparison of absolute measurements with morphometric estimators in sectioned immersion-fixed material.

From a functional viewpoint, the most important part of the small intestinal mucosa is the villus epithelium; in the experimental study of intestinal adaptation it is often necessary to estimate the size of the population. For these reasons, a systematic study of methods of measuring the size of the villus cell population was undertaken in villi of normal morphology from control animals, and in villi of abnormal morphology as produced by treatment of mice with cytosine arabinoside (Ara-C). The villus cell population can be measured with precision and accuracy in both normal and abnormal mucosal states, with a relative standard error usually less than 5%, with good reproducibility, and with very low counting errors. In the mouse a practically linear relationship between the villus cell population size and position in the small intestine can be shown. In normal, control animals, linear estimates of villus population, for example the villus height, the villus core height, and the villus row count measured in sections of immersion-fixed material, were found to be rough approximations as indicators of the villus cell population, and were highly correlated with it. Product variables, comprising the products of a height with a width measurement, show a large improvement over the linear variables as estimators of villus cell population. In populations of abnormally shaped villi produced by Ara-C, both linear and product variables showed a considerable decrease in correlation with the villus cell population. Consequently, indirect, linear measurements of the villus population size do not accurately reflect the size of the villus population in abnormal villi. Finally, a method comparing theoretical and measured surface: volume indices was used to indicate that the most appropriate shape for normal mouse villi is a simple cylinder; this method would also be applicable for other villus cell populations.