ABSTRACT
Radiation enteritis is a significant clinical problem in patients receiving ionizing radiation directed at the abdomen or pelvis. Although radiation therapy is aimed to be directed against the malignant tissue, adjacent healthy tissues are also affected and the small intestine is the most sensitive organ to radiation. Melatonin has been documented as a direct free radical scavenger and an indirect antioxidant, as well as an important immunomodulatory agent. The aim of the research is to study the histological and ultrastructural changes of X-ray irradiation on rat jejunal mucosa and possible radioprotective role of melatonin. Thirty six adult male albino rats were included in the study and were divided into three groups, the first group was included twelve rats and was served as controls, the second group was included 12 rats and was exposed to a whole body X-ray irradiation dose of 8 Grays [Gy]. The third group was included twelve rats and was subjected to intraperitoneal injection of melatonin [10 mg/kg body weight melatonin one hour before irradiation]. The animals were anaesthized at 48 hours after X-ray irradiation and perfused with fixative solution and laparotomy was performed. Immediately after laparotomy, the small intestine [jejunum] was removed. Some specimens of jejunum were fixed in 10% neutral-buffered formalin, embedded in paraffin, sectioned and stained with haematoxylin and eosin. Other specimens were fixed in 5% buffered glutardehyde and electron microscopic technique was made and semithin and ultrathin sections were obtained and examined to show the ultrastructure of small intestine. The results revealed that X-ray irradiation resulting in loss of architecture and disarrangement of cells of the microvilli which have pale cytoplasm and degenerated nuclei with a reduction of mean villous height, mean crypt diameter and mean number of villi per cross section. Also electromicroscopic feature revealed lack of parallel arrangement of microvilli, loss of glycocalyx covering, desquamation of microvilli, vacoulation of apical part of the cells, dilatation of rough endoplasmic reticulum, and damage of mitochondrial cristae. In group of irradiated animals pretreated with melatonin [group three], these changes were improved and the intestinal mucosal structure was preserved. Administration of melatonin prior to irradiation can protect the intestine against X-rays destructive effects