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Introduction: Thyroid hormones are essential for proper development of many system and organs, including circulatory system. Maternal thyroid deficiency accompanies up to 3% of all pregnancies all over the world and may affect the functioning of descendant cardiovascular system in childhood or later in adulthood. However, long-term effects of early thyroid deficiency are poorly understood. We hypothesized that antenatal and early postnatal hypothyroidism will influence anticontractile effect of NO in coronary arteries of adult rats. Methods: In order to model antenatal and early postnatal hypothyroidism females were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%) from the first day of pregnancy till 2 weeks after delivery. Control females were supplied with pure water. Their male offsprings were grown up till the age of 10-12 weeks. Septal coronary arteries were isolated and studied in wire myograph. Blood serum thyroid hormones concentrations were evaluated at the age of 2 weeks (in order to control thyroid status of pups) and 10-12 weeks by ELISA. Results: The average dose of PTU consumed by dams daily was 0.88 mg/kg. The duration of gestation, the number of pups per litter as well as pup body weight didn’t differ between two groups. At the age of 2 weeks male descendants of PTU-treated mothers (PTU group) showed significant reduction of serum levels of total and free T4 and T3 in comparison to pups of control dams (control group). However, at the age of 10-12 weeks thyroid hormones concentrations didn’t differ between groups. Endothelium-denuded arteries of adult PTU and control rats developed strong basal tone in the absence of agonist and their contractile responses to thromboxane A2 analogue U46619 were not different between groups. However, responses to U46619 of endothelium-intact arteries of PTU animals were significantly enhanced in comparison to control group, indicating that endothelium exhibits strong anticontractile effect in control, but not in PTU rats. Further, NO-synthase inhibitor L-NNA (0.1 mM) caused significant elevation of basal tone and U46619-induced contraction of endothelium-intact arteries only in control rats, while had no effect in animals of PTU group. Responses of endothelium-denuded arteries to exogenous NO-donor DEA/NO were similar in two groups. Conclusions: Our data demonstrate that NO-mediated anticontractile effect of endothelium is eliminated in coronary arteries of rats with antenal and early postnatal hypothyroidism, that is not associated with alteration in smooth muscle NO-sensitivity. These findings demonstrate that maternal thyroid hormones deficiency may have serious consequences in adult offspring including coronary circulation pathologies, despite normal blood levels of thyroid hormones. This study was supported by the Russian Science Foundation (grant N14-15-00704).