Therapeutic effect of Ga-Al-As diode laser irradiation on experimentally induced inflammation in rats

We produced experimental inflammation models in rats by carrageenin and studied the effect of Ga-Al-As diode laser irradiation (780 nm, continuous wave, 31.8 j/sec/cm2, spot size of 0.2 mm) on inflamed regions compared with those of indomethacin, a potent anti-inflammatory agent. We found that a low-power infrared laser has an anti-inflammatory effect on carrageenin inflammation. A low-power laser inhibits: (1) the increase of vascular permeability during the occurrence of an acute inflammation in the carrageenin-air-pouch model, (2) edema in the acute stage in the carrageenin-paw-edema model, and (3) the granuloma formation in the carrageenin-granuloma model after receiving laser irradiation once daily. In all cases, irradiation for less than 10 min was sufficient to inhibit the inflammation by 20-30%. The inhibitory effect of laser irradiation was not comparable to that of indomethacin (4 mg/kg, i.o.) in the air-pouch model and the paw-edema model, whereas laser irradiation was more potent than that of daily administration of indomethacin (1 mg/kg, i.o.) in the granuloma model. In future studies of the mechanism of laser effect, it should be noted that irradiating a rat twice, before and after the provocation of inflammation, was essential in order to achieve an effective inhibition of paw-edema.