The objective of this research was to indirectly determine the existence of a possible retinal-endocrine pathway activated, or Inhibited, by artificial fluorescent light as evidenced by it subsequent effects on bone metabolism. Forty-eight male Long-Evans post-breeder rats, half of which were bilaterally orbitally enucleated, were used in this experiment. A 21-day pretreatment diet contained calcium and phosphorus, each at a level of 0.2% of the diet, with no dietary vitamin D. During the last seven days of this period the animals were in complete darkness. For the 12-week experimental period, the diet contained 0.6% calcium and 0.4% phosphorus, and oholecalciferol wets administered the first day by intubation. During this time, four groups of 12 animals each, half of which were bilaterally orbitally enucleated, were exposed to either ultraviolet lights, cool green lights, Vita-Lite (full spectrum) lamps, or kept in complete darkness in specially constructed environmental boxes. On the first and last day of the experimental period, the left femurs were x-rayed and blood was sampled. The serum of the animals was analyzed for alkaline phosphatase, total calcium and total phosphorus. Bone density was determined. Femur ash was measured for total calcium and total phosphorus. Under all lighting conditions, for both the sighted and enucleated rats, the parameters measured in the serum declined. For serum alkaline phosphatase, the sighted rats under the cool green lights had the least change; the sighted in darkness had the greatest decline. The least change in serum total calcium occurred for both the sighted and enucleated rats under the cool green lights, whereas the greatest decline was for the sighted rats under the Vita-Lite lamps and the enucleated under ultraviolet lights. The sighted rats under the cool green lights had the highest percent ash per gram of dry fat-free weight; the sighted under the Vita-Lite lamps had the lowest. The highest ash calcium was in the sighted rats under the cool green and the Vita-Lite lamps. By both methods of bone density measurements, specific gravity and densitometry, the sighted rats under the cool green lights had the greatest loss. Overall there appeared to be more significant differences among the sighted animals for the various lighting conditions than for the enucleated. Also the enucleated rats had less extreme variations from the mean than the sighted. The results of this study suggest that the light mediated by the pbotoreceptors of the retina of the sighted rats produced an effect on bone metabolism. / Graduation date: 1982

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