环一磷腺苷对小鼠U_(14)实体瘤超微结构的影响

<正> 环一磷腺苷(cAMP)能控制肿瘤细胞的生长,恢复体外培养中恶性转化细胞的正常形态和接触抑制,促进分化,已有许多文献报导,但cAMP的作用机制不清楚,cAMP能引起体内细胞,特别是恶性细胞内部微细结构的哪些变化,报告极少。我们在以前的研究中证明cAMP对小鼠移植瘤U_(14)有明显的抑瘤作用,抑制率达56.8～88.9％,肿瘤生长

THE EFFECT OF CYCLIC ADENOSINE MONOPHOSPHATE ON THE SUBMICROSCOPIC STRUCTURE OF MOUSE SOLID TUMOR U_(14) CELLS

The electron microscopic changes of mouse solid tumor Uncells caused by cAMP were examined to investigate the mechanism of its inhibitory ac- tion and tumor regression. The most prominent changes induced by cAMP were those of ribosome including the degranulation of polyribosome from rough endoplasmic reticulum and the reduction of free ribosomes in cytoplasm. The amount of scattered ribosomes increased in a few cells, whereas great majority of cells contained less ribosomes. These alterations give rise to a state of complete disorganization of ribosomes. Sinee protein synthesis takes place in polyribosome, the disorganization of ribosome may be considered as a morphological feature of reduced protein synthesis. The degranulation of polyribosome from endoplasmic reticulum into cytoplasm is a relative mild injury and in more advanced case, ribosomes on membranes and in cytoplasm are diffusely reduced. Our study has demonstrated that cAMP causes pronounced disorganization of ribosomes in solid tumor cells and leads to pronounced reduction of protein synthesis. Tumor growth is apparently inhibited together with disorganization of ribosomes. The process of tumor growth and its modulation is a very complicated problem. Our work in connection with other biochemical result may suggest that the inhibition of membrane transport of certain substances and the reduction of RNA or protein synthesis probably arc the important mechanisms for arrest and even regression of tumors.Mitochondria hypertrophied and some giant mitochondria were observed in tumor cells after 8 injections of cAMP. Those in cells after 10 injections were swollen. The former change of in mitochodria may be compensatory hypertrophy of organelles produced by mild injury , while the later presumably is the change of degenerated cejjs occured after reduction of protein synthesis.