Intestinal Crypt Survival and Total and Per Crypt Levels of Proliferative Cellularity Following Irradiation: Fractionated X-Ray Exposures

The split-dose response of jejunal crypt survival has been measured for first exposures of 1000 or 600 R (1400 R total exposure). The curves obtained are analyzed in terms of repair of sublethal damage, progression through the cell cycle, and alterations in multiplicity commencing after the G2block. The maximum survival ratio for that portion of the curves which probably represents repair of sublethal damage is 3-4, which is considerably less than anticipated from previous studies on single-dose crypt survival. Total and per crypt levels of proliferative cellularity have been measured 3 days following the second exposure. These curves represent the net result of perturbing a complex steady-state in vivo system and are but partially conducive to temperate analysis at this time.