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Due to the presence of contradictory results about the effect of dopamine on the synthesis and secretion of thyroid hormones, as well as the absence of this information in clinically healthy individuals, we were interested in studying this problem in permanent residents of the Arctic territories, which are characterized by high thyroid activity and dopamine content. The aim of this work was to study the hormone levels of hypothalamic-pituitary-thyroid axis (HPTA) under the different levels of dopamine in the blood of permanent residents of the Arctic territories. Materials and Methods: We examined 316 healthy individuals (the indigenous population, mestizos, and the local Russian population) born and permanently residing in the territories of the Russian Arctic zone. The examined participants were divided into 3 groups: Group 1 with undetectable levels of dopamine in the blood (0 nmol/l); Group 2 with reference levels of dopamine (<0.653 nmol/l); and Group 3 with increased levels of dopamine (>0.653 nmol/l). The serum levels of TSH, T4, free T4, T3, and free T3, and the plasma dopamine level were determined by enzyme immunoassay. The plasma cAMP level was determined by radioimmunoassay. Results: In individuals of Group 1, there was a decrease in the activity of hypothalamic-pituitary-thyroid axis (HTPA) and the peripheral conversion of iodothyronines compared with persons with reference or increased dopamine levels. In individuals of Groups 2 and 3, we found an increase in the activity of HTPA with an increase in the blood level of dopamine. The absence of the inhibitory effect of high levels of dopamine on HPTA hormones in the examined individuals may be a compensatoryadaptive response of the body under the conditions of permanently acting extreme factors of the North.

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