[Bone marrow and thymus lipids in rats irradiated with continually decreasing doses of gamma rays]

Male SPF Wistar rats were continuously irradiated over 10 days on an open experimental field with gradually decreasing doses of gamma radiation. The total accumulated dose of radiation was 6.5 Gy for 3 days, 8 Gy for 6 days, and 9 Gy for the overall period of 10 days. The controls consisted of non-irradiated animals from the area of the experimental field and of intact animals from the animal room. Except for a temporary increase in total cholesterol level, no marked changes in serum lipid concentration were observed during the irradiation period. The content of triacylglycerols (TG) in the thymus decreased only nonsignificantly during irradiation. The content of thymus phospholipids (PL), which was depressed during the irradiation period, recovered in the early stage after termination of irradiation. A dose-dependent increase in TG was recorded in the bone marrow, with values remaining elevated after irradiation and showing a secondary peak two months later. They returned to normal levels only 240 days after termination of irradiation. Bone marrow PL decreased during irradiation and recovered soon after termination of the exposure period. The changes of TG concentration in the bone marrow reflect the appearance of increased adipocyte formation and may serve as an indicator of altered hematopoietic stroma reaction, especially in the evaluation of late irradiation effects.