[Effect of preparations melatonin and epitalon on the age-related dynamics of thyrotrophic activity of the hypophysis and thyroid gland function in different light regimes].

The influence of different light regimes (standard lightning--12 hours light/ 12 hours darkness; natural light regime of the North-West of Russia; constant darkness and constant lightning), melatonin and epitalon on the thyrotrophic activity of hypophysis and on the function of thyroid gland was studied. It has been found out that the maximum values of free thyroxin and triiodothyronine in blood were observed in the conditions of constant lightning and the minimal values--in the conditions of light deprivation. In the conditions of natural lightning of Karelia, with orientation on seasonal lightning, the following annual-circadian rhythms were observed: in autumn (period of short lightness duration) the level of free T3 was the lowest; in spring (period of short darkness duration) it was the highest; the inverse relationship was observed by the comparison of free T4 concentration. The lowest values of TSH were observed in old rats kept in constant light and natural light regimes. The concentration of TSH in blood was practically on the same level in the standard regime and in the regime of light deprivation. The age changes of the level of hormones appeared later in rats who received medication, in comparison with the control sets of animals. The use of melatonin and epitalon smoothened the seasonal variations of the level of thyroidal hormones in blood in the lightning conditions of Karelia.