ИСТИНА

Thyroid hormones are key regulators of the developmental processes. Their deficiency during early stages of development (prenatal and early postnatal) delays growth and functional maturation of different body systems, including cardiovas-cular system. However, hypothyroid-associated alterations of vascular smooth muscle during early postnatal period are poorly understood and their mechanisms are not explored at all. We hypothesized that the deficiency of thyroid hormones in antenatal and early postnatal periods will affect the regulation of contractile re-sponses in arteries of young progeny, in particular, by affecting smooth muscle cell differentiation processes as well as Rho-kinase pathway activity (this pathway is particularly important for vasomotor control in perinatal age). To test this hypothesis we used the model of antenatal and early postnatal hypothyroidism. Dams were treated with propylthiouracil (PTU) in drinking water (0.0007%) during the whole gestation period and two weeks after delivery. Two-week-old male offspring from dams treated with PTU (PTU group) in comparison with the control offspring demonstrated a marked reduction of thyroid hormones in the blood: total T4 concentration was reduced by 79%, free T4 – by 87%, total T3 – by 94% and free T3 – by 68%. Blood concentration of thyroid stimulating hormone was compensatory increased by 50 times in PTU group compared to the control. Vasoregulatory effects of thyroid deficiency in 2-week-old offspring were studied using small mesenteric arteries, where we measured: (i) contractile responses to α1-adrenoceptor agonist methoxamine (wire myography); (ii) mRNA contents of actin isoforms (markers of smooth muscle cell maturation), RhoA (Rho-kinase activator) and CPI-17 (one of Rho-kinase targets) (qPCR); and (iii) the content of Rho-kinase α protein (Western Blotting). The isometric contractility (maximum active force) of the vascular wall was smaller in arteries of PTU group in comparison to the control group. Maximum active force is mainly determined by the thickness of smooth muscle layer in the wall. Along with that, the contractility of developing arteries is known to depend on the maturity of their contractile apparatus. Vascular smooth muscle differentia-tion is marked by the switch of actin isoforms expression, so that β-actin is replaced by smooth muscle α-actin. In mesenteric arteries of PTU rats the ratio of α-actin mRNA to β-actin mRNA was two-fold smaller compared to that in control rats. To evaluate the role of Rho-kinase in the regulation of contraction in con-trol and PTU rats we used Rho-kinase inhibitor Y27632 (3 μM). Incubation with Y27632 significantly reduced the contractile responses to methoxamine in both groups. However, the effect of Y27632 was more prominent in PTU group com-pared to control, which indicates an increased contribution of Rho-kinase to the regulation of arterial contraction. The increased functional role of Rho-kinase in mesenteric arteries of PTU rats was observed along with elevated Rho-kinase pro-tein content and elevated level of CPI-17 mRNA, while the level of RhoA mRNA was similar in both groups. In conclusion, our data show that antenatal and early postnatal hypothyroid-ism delays vascular smooth muscle cells differentiation and augments the func-tional role of Rho-kinase in small mesenteric arteries. Notably, the increased activi-ty of Rho-kinase pathway is a hallmark of various cardiovascular pathologies. In this study, we demonstrated, for the first time, its association with antenatal and early postnatal hypothyroidism. Supported by the Russian Science Foundation (Grant N 14-15-00704).