Determination of X-ray-induced damage to the murine colon using tissue compliance measurements.

A proctometroscope has been developed to measure the mechanical functioning of the colon in a murine model. A balloon-tipped probe is inserted into the colorectal region of anaesthetized mice and inflated hydraulically, at a constant rate, by a motor-driven syringe. Balloon pressure and volume are monitored, processed and plotted on a X-Y/t recorder. The balloon is inserted within the irradiated area, such that the centre of the balloon is 1 cm proximal to the anus, and inflated up to either a maximum volume of 100 microliters or a maximum pressure of 100 cmH2O, depending on which occurs first. Compliance (delta V/delta P) of the colon was measured at various intervals following X-irradiation, a dose-dependent decrease being observed at 24 weeks. This decrease was progressive with time out to 72 weeks postirradiation. The compliance measured, in both control and irradiated groups, was not dependent on the inflation rate used to make the determination, and no iatrogenic effects have been detected after repeated probing during a long-term study. The use of different anaesthetic agents was also investigated, no significant difference between the compliance of mice anaesthetized with the different agents being detected. Use of this technique provides fully quantitative data on the function of the colon following radiation injury, and provides an alternative to other physiological assays. The technique is non-destructive, rapid, easy to use and non-invasive to the tissue, thus the onset and progression of damage can be followed in each mouse over long postirradiation periods.