The effect of pelvic irradiation on the absorption of bile acids

The pathophysiology of radiation-induced diarrhea was evaluated in 17 patients undergoing pelvic irradiation for gynecological malignancies. The glycine conjugates of cholic acid (GC) and chenodeoxycholic acid (GCDC) were measured in serum by radioimmunoassay. Fasting and 2 hr post prandial (pp) determinations were performed prior to and in the fifth week of radiotherapy. The pre-treatment fasting and 2 hr pp GC levels were 0.20 ± 0.29 (mean ± SD) and 0.48 ± 0.47 μM. In the fifth week the fasting and 2 hr pp GC levels were 0.16 ± 0.23 and 0.25 ± 0.27 μM. The first week fasting and 2 hr pp GCDC levels were 0.32 ± 0.47 and 0.80 ± 0.83 μM: in the fifth week they were 0.10 ± 0.06 and 0.33 ± 0.27 μM. The differences between the first and the fifth week post prandial increases in serum GC and GCDC levels were significant (p < 0.02). The reduced post prandial increases in serum GC and GCDC in the fifth week of radiotherapy occurred at a time when the patients' daily stool frequencies were significantly increased (P < 0.01). The data suggest that a cholerrheic enteropathy is the major determinant in the pathophysiology of radiation-induced diarrhea.