[Absence of photoperiodism and digestive enzymes in rats: the role of the age and endogenous melatonin level.].

We studied the effect of prolonged absence of a photoperiodic signal (constant lighting and constant darkness) on the changes of digestive enzymes' activity in late postnatal ontogenesis of rats. Age-related alterations are characterized as a change in activity of enzymes, as well as a redistribution of the functional activity between the amylo- and lipolytic links, the upper and lower divisions of the gastrointestinal tract. It was shown that along with age, the activity of enzymes is affected both by the absence of photoperiodism and by the level of melatonin associated with the light regime. In conditions of light deprivation the age-related changes characterizing the «aging» of the digestive system are observed later compared with standard illumination and especially constant illumination.