下丘脑─垂体─肾上腺皮质轴功能变化在低剂量辐射诱发免疫增强机制中的作用

Role of changes in functional stains of hypothalamic-pituitary-adrenocortical axis in immunoenhancement after low dose radiation

７５ｍＧｙＸ射线全身照射后下丘脑５羟色胺（５－ＨＴ）含量升高，血清ＡＣＴＨ和皮质酮（ＣＳ）水平降低，伴有胸腺和牌细胞免疫功能增强．下丘脑内注入５－ＨＴ引起血清ＡＣＴＨ下降的同时，导致胸腺和牌细胞免疫反应性上升．作者认为，低剂量辐射引起植物神经中枢５－ＨＴ能性神经元兴奋，使下丘脑内５－ＨＴ增多，同时垂体分泌ＡＣＴＨ减少，导致肾上腺皮质功能下调，部分解除下丘脑－垂体－肾上腺皮质系统对免疫器官的张力性抑制，从而诱发免疫功能增强。这是分析低剂量辐射兴奋效应的机制时应当考虑的一个重要因素．

Whole-body irradiation (WBI) of mice with 75 mGy X-rays caused inrcease in 5-hydroxytryptamine (5HT) content of hypothalamus and decrease in serum adrenocoricotrophic hormone (ACTH) and corticosterone (CS) level.accompanied with potentiation of immune functions, expressed as increased spontaneous incorporation of 3H-TdR into thymocytes, augmented proliferative reaction of the splenocytes to Con A and increased production of interleukin-2 by the splenocytes. After intrahypothalamic injection of 5HT there occurred a lowering of serum ACTH level and enhancement of immune reactivity of the splenic and thykic lymphocytes. It is assumed that foxy dose radiation could influence tile central 5-hydroxy-tryptaminergic neurones causing increase in hypothalamic 5HT content and this, in turn. decreases pituitary secretion of ACTH with a down-regulation of the adrenocortical function. This would partially release the tonic suppression normally exerted on the immune organs by the hypopthalamic-pituitary-adrenocrtical axis, thus leading to poteqtiation of immune functions. These neuroendocrine changes should be considered as an important factor in the analysis of the mechanism of immunoenhancement after WBI with low doses.