Recently, much attention has been paid to the analgesic and anti-inflammatory effects of low power laser irradiation.However,the mechanism remains unclear. In the present study, we have performed experiments of in vitro laser irradiation on cultured synovial cells from patients with RA in order to investigate the effect on DNA synthesis.
Cultured synovial cells were prepared from synovial tissue obtained during knee joint surgery from six patients with RA. A continuous wave He-Ne laser was irradiated on the cells, with a wave length of 632. 8 nm and a power output of 8.5 mW±20% (11.5 mW measured). Following the irradiation at energy densities varying from 5 to 2000 mJ/cm², DNA syntheses of irradiated cells were measured by ³H-thymidine incorporation.
In all six cases,DNA synthesis was significantly inhibited,but each of the cultures showed a different inhibitory response to the irradiation.Morphological observation by a phase-contrast microscope revealed no destructive change by heat energy of laser irradiation.
Thus, the results suggest that, under the conditions in this experiment,low power He-Ne laser has a direct effect on cultured synovial cells from patients with RA, and inhibits aberrant cell proliferation through a certain non-thermal action mechanism.

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To investigate the mechanism of tumor cell destruction by hyperthermia using Nd: YAG laser (laser thermia) in vivo, we studied on tumors of the mice which were subcutaneously inoculated Lewis lung carcinoma. After the treatment with laser thermia at 43±0.5°C for 10 minutes with 2.0 watts out put power, we serially observed the pathohistological and electron microscopical changes in the tumor cells and tissue.
1) Pathological changes: Immediately after the treatment, congestion of the vessels and mild hemorrhage in the tumor were observed. But the tumor cells did not show any morphological alternations. Three hours after the treatment, the hemorrhage in tumor was expanded, and the degenerative changes were observed in the nuclei of tumor cells. Six hours after,shrinking in nuclei and reducing in cell volume were observed. Finally, all of the tumor tissue showed hemorrhagic necrosis 24 hours after.
2) Electron microscopic changes: Immediately after hyperthermic treatment, swelling of mitochondria with ruptured cristae were observed. Three hours after treatment, degeneration in nuclei and mitochondria were manifested. All tumor cells were destroyed after 24 hours. These results suggest that mitochondria is the first target in the tumor cells treated with laser thermia.

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