The effects of exposure to continuous light, continuous darkness, and administration of melatonin on prostatic androgen receptors in relation to pubertal development in rats were examined. Darkness produced dissimilar results between the pubertal and adult groups. Whereas the prostate weight in the pubertal group remained unaltered, it increased in the adult group. In the pubertal group exposed to darkness, plasma melatonin increased significantly, and androgen receptors declined, whereas in the adult group these receptors rose significantly with a simultaneous increment of melatonin concentration in plasma. Exposure to continuous light did not produce any effective alterations in the parameters examined. The afternoon melatonin administration showed trends similar to those seen in animals exposed to darkness. The results indicate that exposure to darkness or administration of melatonin both have age-dependent effects on prostatic androgen receptors. Exposure to darkness may interfere with the process of sexual maturation in the pubertal animal as a result of increased melatonin production.

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