The effect of chronic stress on neutrophil function in tumor-inoculated rats

OBJECTIVES: In order to clarify the relation between stress load and inoculated tumor growth in conjunction with neutrophil functions, several kinds of stress such as physical (Ph) and psychological (Ps) stress were loaded on rats either SST-2 tumor cell inoculated or control, and the functions of their peripheral neutrophils were determined. METHODS: A communication box was used for stress load on rats. SST-2 cells were inoculated in to rats in the tumor-inoculation groups. Two weeks after inoculation, the tumors were removed from the backs of the rats and weighed. The functions of neutrophils in the peripheral blood collected from the tail vein, were determined by the NBT deoxidization method. RESULTS: Tumor growth was enhanced when rats were loaded with either Ph or Ps stresses, but was inhibited when tumor cells were inoculated following either Ph or Ps stresses. These results show that chronological differences of loaded stresses influence immunological functions differently. The O2- production from the neutrophils stimulated by NBT-treated Staphilococcus aureus was suppressed in tumor-inoculated Ph and Ps groups, more markedly in the tumor-inoculated Ph group. It is logically relevant that the size of tumors increased in these groups, predominantly in the tumor-inoculated Ph group. On the other hand, O2- production from the neutrophils was enhanced and tumor growth decreased in tumor-inoculated animals following either Ph or Ps stresses. CONCLUSIONS: Our experiments, it revealed that the function of neutrophils is strongly enhanced by stress load and O2- production is inhibited by the tumor inoculation as shown in stimulation tests. Therefore, our findings suggested that neutrophils may participate in the inhibition of tumor growth.