Clonogen content of intestinal crypts: its deduction using a microcolony assay on whole mount preparations and its dependence on radiation dose.

A new method for detecting surviving intestinal microcolonies in whole mount preparations is presented. This approach is not subject to the sampling problems encountered with microcolony assay using data from tissue sections, associated with the size of the microcolonies and the random nature of the sections in relation to these colonies. This new method has been used to determine the crypt survival after one or two fractions of gamma-irradiation, and hence to estimate the crypt clonogen number. The survival levels are similar using the two techniques and similar estimates for the number of clonogens per crypt are obtained. The results using this novel approach thus confirm the validity of the traditional approaches using sections. The estimates of initial clonogen number per crypt show a dependence on the size of dose used to estimate the number, and the estimates range from about eight clonogens per crypt for doses between 7 and 8 Gy, to about 40 clonogens per crypt for doses between 9 and 10 Gy.