en Radiation Biology Radiation Biology تحقيق بديع Original Research <span style="font-weight: bold"> Background:</span> Study of vascular and its secretory profile changes is an important issue in pathogenesis of radiation myelopathy. This paper reports the prostacyclin concentration changes after low-moderate doses of X-irradiation within a short period of time. <span style="font-weight: bold">Materials and Methods:</span> Cervical cords of Wistar rats were irradiated to doses of 0.5, 1, 2, 4 and 6 Gy X-rays. After 24 hours, 2 and 13 weeks post-irradiation, prostacyclin contents were quantified and cords specimens were also stained routinely for histological studies. <span style="font-weight: bold">Results: </span>Twenty four hours post-irradiation, showed a decrease in the content of prostacyclin after doses of 0.5 and 1 Gy 91.67±1.47% 96.80±2.17% of respectively age-matched control group. After 2 weeks the concentration of prostacyclin showed significant decreases after 6 Gy. After 13 weeks irradiation shows marked differences even after a small dose of 2 Gy (p<0.001), and after doses of the low dose group. The differences between concentration values at doses of 4 Gy and 6 Gy were significant in comparison with the control (p<0.001 and p<0.002, respectively). <span style="font-weight: bold">Conclusion: </span>Results suggested that the response of the vascular tissues to low and moderate doses of radiation occurs prior to that of the nervous tissue of the spinal cord. It means that the asymptomatic interval after radiation is characterized by sequential physiological changes which are imperfectly reflected in routine histological study and that even in the histologically unaffected spinal cord severe impairment is present in substructures and biochemistry of irradiated spinal cord. Prostacyclin, radiation myelopathy, low irradiation dose, time effects 129 136 http://ijrr.com/browse.php?a_code=A-10-1-212&slc_lang=en&sid=1 S.R. Mahdavi srmahdavi@hotmail.com 79003194753284600626 79003194753284600626 Yes A.R. Nikoofar 79003194753284600627 79003194753284600627 No H.R. Mirzaee 79003194753284600628 79003194753284600628 No B. Mofid 79003194753284600629 79003194753284600629 No R. Mohammadi 79003194753284600630 79003194753284600630 No