Background: The present study was aimed to identify how age-related changes in some
physiological and biochemical systems are related to changes in the life span of rats with long-term
pineal gland hypo- and hyperfunction induced by constant light and constant darkness, respectively.
Methods: At the age of 25 days the rats were randomly divided into 3 groups: standard light/dark
regimen (LD), constant light (LL) and constant darkness (DD). Age-related Antioxidant System
(AOS) changes in liver tissues, alteration of immunoreactivity in blood smears were investigated,
pubescence and lifespan of the animals were determined.
Results: Modification of the level of melatonin synthesis induced by constant light results in interrelated
rearrangements in the functioning of the investigated physiological systems. Elevated activity
of the antioxidant system extends the lifespan, while at the same time slowing down pubescence and
altering the morpho-functional properties of leukocytes in blood.
Conclusion: The absence of light/dark alternation (constant light and constant darkness) affects only
those physiological indices that follow the organism’s circadian rhythms (Activity of Antioxidant
Enzymes (AOE), levels of individual immune system cell types), whereas changes in the parameters
not governed by circadian fluctuations (vitamin concentrations, pubescence, and aging) depend on
the level of melatonin produced by the pineal gland.