Intestinal crypt survival and total and per crypt levels of proliferative cellularity following irradiation: fractionated x-ray exposures.

A radiation survival curve for intestinal crypts has been obtained. It is characterized by a D0 of 330 R and n of 10. Crypt survival is quantitatively similar for assays performed at 3 and 4 days following irradiation, although crypt size varies considerably during this interval. An as yet unexplained discrepancy exists between the crypt survival curve obtained experimentally and that predicted from crypt cell survival parameters and compartment size. Proliferative crypt cells appear to constitute the intestinal stem cell compartment. Recovery in terms of cellularity occurs even following exposures as high as 1400 R. It seems critical for 5-day survival of the animal that proliferative cellularity reaches some requisite level by day 3 following exposure; later increases in cellularity are not reflected by increased 5-day survival. It appears from this that crypt survival is an important feature with respect to 5-day survival of the irradiated animal.