EFFECT OF MELATONIN ON THE ULTRASTRUCTURE OF ENTEROCYTES IN RATS AFTER TOTAL BODY IRRADIATION

The intestinal absorptive cells "enterocytes' represent the most common cell lineages covering the intestinal villi. These cells are considered as the most rapidly renewing tissues of the body and hence. they are very sensitive to the effects of various cytotoxic insults (Burkitt et al., 1993).
In the field of radiotherapy, ionizing radialion is used to damage target cells or tissue. However, the irradiation also damages the non-target cells or tissues (von Sonntag, 1987). The high sensitivity of the gastrointestinal tract to ionizing radiation renders it a possible target in accidentally exposed persons and a dose limiting tissue in some radiotherapy practices. It was also, reported that the damage to the gastrointestinal tract seems to be of primary concern for the local Xvirradiation of abdominal or pelvic tumors. as well as [or the Whole-body X-irradiation preceding bone marrow transplantation (Otchy and Nelson, 1993; Allgood et al., 1996). A large number of clinical reports on radiation enteritis or radiation-induced enteropathy was recorded after the use of different radiation therapy protocols for the treatment of abdominal or pelvic tumors (Olasoto, 1989; Busch, 1990). However, despite of the constant renewal of the irradiation schemes as well as radiation sources and qualities used. the occurrence of radiation enteritis is incr -asing due 10
the increasing number of cancer patients requiring radiotherapy (Allgood et al., 1996). It was reported that ionizing radiation-induced mucosal atrophy is often complicated by ulceration. existence of atypical hyperplastic glands and cystic glandular inclusions. intestinal wall fibrosis. obliterated vascular sclerosis and lymphatic dilatation (Hauer-Jensen, 1990). In clinical terms. the effects of the ionizing radiation on the gut could be grouped into two main categories: prodromal effects that OCcur  at relatively low doses of exposure (1 Gy) and the gastrointestinal syndrome occurring after higher radiation doses (> 10 Gy). As to the time course of events, ionizing radiation effects in the gut have been staged as the initial phase (l . 3 days after exposure) followed by the acute, subacute and late phases of the manifest illness(Anno et at, 1989; Rubio and JaJnas, 1996).