Ablation of murine jejunal crypts by alkylating agents.

The gut microcolony assay has been used to measure damage to intestinal crypts by single and split doses of 3 alkylating agents: mechlorethamine hydrochloride (HN2), bis-chloroethyl-nitrosourea (BCNU) and isopropyl methane sulphonate (IMS). The single-dose survival curves for whole crypts were distinguished by extrapolation numbers (3.0, 176 and 1.5 respectively) that were lower than most previously published values for assay by irradiation. Significant sparing of crypts occurred when doses of HN2 or BCNU, but not IMS, were given in 2 equal fractions separated by more than 2 h. Deduced D0 values for those cells from which crypts regenerate were 1.9 mg/kg HN2, 19 mg/kg BCNU and 487 mg/kg IMS.