Effects of 400 R whole-body x-irradiation on 5-hydroxytryptamine content of the rat gastrointestinal tract.

The effects of a single 400 R whole-body dose of X-irradiation on the regional 5HT content of the gastrointestinal (G. I.) tract were studied from four hours to 40 days after irradiation. The total 5HT content of various G.I. tissues was determined and 5HT was also determined per unit of body weight, wet weight of tissue and tissue protein. Irradiation caused an immediate decrease of the amine content of various G.I. regions in adult rats. This was followed by recovery, the degree of which varied in different regions. Some minor morphological changes were seen in enterochromaffin cells one and two days after irradiation but not later. The effects of irradiation on the G.I. tissues were stronger in young rats, in whom no complete recovery of 5HT occurred within 45 days. The present results support the view that irradiation exerts a direct damaging effect on the gastrointestinal 5HT storage, which is associated with liberation of 5HT from amine-containing cells. The duration of the effect varies with age and intestinal segment concerned.