[Study of the photoperiodic dynamics of the peripheral dopamine content in comparison with the thyroid profile in various groups of men from the European North].

Background: Knowledge of the physiological mechanisms of adaptation arising in response to changes in photoperiods is especially important for residents of the European North. In the literature, there is practically no information about photoperiodic dynamics of serum dopamine level, despite its significant role in the regulation of the body's activity. The mutual modulating effect of the dopaminergic and thyroid systems is known.

Aim: To show the ratio of dopamine levels and the content of hormones, protines and autoantibodies of the thyroid system, taking into account photoperiod of the year, in practically healthy populations of the European North.

Materials and methods: Healthy male population (20 men) of Arkhangelsk was examined in various photoperiods of the year (80 samples): an increase in the length of daylight hours (March), its maximum duration (June), a decrease (September), and a minimum duration (December). The inhabitants of the settlements and the nomadic aboriginal population (100 men) were examined during 2 photoperiods of the year - March and December. The serum levels of iodothyronines, TSH, TG, antibodies to TPO, antibodies to TG and plasma level of dopamine were determined using ELISA methods.

Results: Residents of Arkhangelsk in June compared to December have higher levels of dopamine (0.502 and 0.365 nmol/l, p=0.01), T3 (1.09 and 0.94 nmol/l, p=0.003), T4 (113.45 and 99.03 nmol/l, p=0.0002). In September, compared with June, a decrease in dopamine (0.235 nmol/l, p=0.0003), T3 (0.92 nmol/l, p=0.004) was recorded with an increase in T4/T3 ratio from 106.54 to 117.89 units (p=0.006). The nomadic aboriginal population in March compared with December showed a tendency to a higher content of dopamine (0.00 and 0.394 nmol/l, p=0.07) with the decrease in fT4 (15.20 and  13.90, p=0.015), fT4/fT3 ratio from 3.13 to 2.28 units (p=0.006). In December, 67% of nomadic population had undetectable dopamine values (0 nmol/l) and 22% - excess dopamine values, in March 27% - excess values.

Conclusion: Unidirectional changes in dopamine and thyroid activity in men of the European North were shown with their decrease during periods of decrease and minimum daylight hours and an increase during periods of increase and maximum daylight hours.