Sexual Maturation and Ovarian Metabolism in Immature Rats Raised in Various Environmental Lighting Regimes

Immature female rats were used to study sexual maturation as a function of duration, intensity and spectral composition of environmental lighting. Pups were raised in experimental illumination from birth. They were inspected for vaginal opening from the twenty-ninth day of age and sacrificed both before and after the introitus. Ovaries and uteri were collected and weighed at each sacrifice. Ovaries were retained for sterol assays. Lengthy durations of exposure to white light were found to advance the onset of puberty. When various illumination intensities were tested in 14-hour photoperiods, animals in 30-100 lux as well as those in 1666- 2400 lux matured more quickly than did those in the intermediate range of 350-600 lux. However, 24- hour photoperiods masked the differential intensity effects, apparently because the increased duration of light exposure combined with all intensities tested to yield total amounts of light which were stimulatory. The spectral composition of prevailing illumination effected both intensity and wavelength-correlated modifications of the maturation process. Fourteen-hour light of 1666 lux or greater clearly advanced puberty while 350 lux light retarded it. Twenty-four-hour photoperiods of various colors of illumination combined with light intensity, as in previous studies, to yield a total amount of light which was stimulatory in all instances except those involving short wavelengths. Those animals which experienced precocious puberty also desplayed decisive declines in both free and esterified cholesterol as early as 11 days before vaginal opening. Sterols remained low and were not resynthesized until vaginal opening. Animals which matured later maintained free cholesterol pools at steady low levels over the entire two-week sampling period. Esterified cholesterol among the latter groups showed no dramatic decline other than that which occurred immediately prior to the introitus