Although a number of studies have been carried out to examine the biological effects of radiation and ultraviolet radiation (UV), little is known concerning the effects of visible light. In the present study, exposure of B16 melanoma cells to blue light (wavelength 470 nm, irradiance 5.7 mW/cm 2 ) from a light-emitting diode (LED) inhibited cell growth in proportion to the period of exposure, with no increase observed in the number of dead cells. The number of B16 melanoma colonies that formed after exposure to blue light for 20 min was only slightly less than that in non-exposed controls, but the colony size as assessed by the area covered by colonies and cell counts per colony were markedly decreased. The percentages of G0/G1 and G2/M phase cells were markedly increased, with a reduction in S phase cells as determined by flow cytometry after exposure to blue light. Furthermore, analysis of the incorporation of 5-bromo-2′ ′ ′ ′-deoxyuridine (BrdU) into DNA also showed a reduction in the percentage of S phase cells after exposure. These results indicate that blue light exerts cytostatic effects, but not a cytocidal action, on B16 melanoma cells.

12-O-Tetradecanoylphorbol-13-acetate (TPA) was applied to the back skin of v-Ha-ras (TG-AC) female transgenic mice at a dose of 2.5 µ µ µ µg/200 µ µ µ µl twice a week for 9 weeks. The back skin was then exposed to blue light (wavelength, 470 nm; irradiance, 5.7 mW/ cm 2 ) for 1 h daily for 9 weeks. The mice to which TPA was applied developed skin tumors at 6 weeks after the start of application. The tumor incidence rates at 6, 7, 8 and 9 weeks after the start of application were 70%, 80%, 100% and 100%, respectively, and the numbers of tumors 1 mm or more in diameter were 1, 5, 10 and 19, respectively. In the mice that were exposed to blue light after TPA application, the tumor incidence rates were 10%, 40%, 60% and 80%, respectively, and the numbers of tumors 1 mm or more in diameter were 0, 2, 5 and 9, respectively. Histopathological examination of the skin revealed that TPA application induced diffuse hyperplasia, exaggerated keratinization, and papillomas in all 10 mice. A localized form of epidermal hyperplasia was also observed in 4 mice. The incidence rate of papillomas in the mice that were exposed to blue light after TPA application was lower and the degree of exaggerated keratinization was greater. Exaggerated keratinization was considered to represent a regressive change following exposure.

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Chronological changes in hemodynamicsand histopathological lesions of the brain were investigated in rats given a single dose of hypertonic glucose solution (osmotic ratio: 6.5) intravenously or intraperitoneally.After administration, dehydration developed rapidly and markedly but recovery was noted on the following day. An excess dosage of the hypertonic solution caused cerebral lesions with meningeal hemorrhage showing nervous signs.Shrinkage of neurons, and loosening and vacuola tion of the ground substance with swollen astrocytes (spongy appearance) were seen mainly in CA4 subfield of the hippocampus.The spongy appearance occurred in cases which died 130min or later post-administration (PA), while the ischaemic change consisting of necrosis and loss of neurons with glial proliferation was seen mainly in CA1 and CA4 of cases sacrificed 14 days PA. The cerebral lesions showed selective vulnerability and were considered to result from ischaemia caused by hemodynamic changes.