Reactive oxygen species augment contractile responses of saphenous artery in 10-15-day-old but not adult rats: Substantial role of NADPH oxidases.

Reactive oxygen species (ROS) produced by NADPH oxidases (NOX, a key source of ROS in vascular cells) are involved in the regulation of vascular tone, but this has been explored mainly for adult organisms. Importantly, the mechanisms of vascular tone regulation differ significantly in early postnatal ontogenesis and adulthood, while the vasomotor role of ROS in immature systemic arteries is poorly understood. We tested the hypothesis that the functional contribution of NADPH oxidase-derived ROS to the regulation of peripheral arterial tone is higher in the early postnatal period than in adulthood. We studied saphenous arteries from 10- to 15-day-old ("young") and 3- to 4-month-old ("adult") male rats using lucigenin-enhanced chemiluminescence, quantitative PCR, Western blotting, and isometric myography. We demonstrated that both basal and NADPH-stimulated superoxide anion radical (O2•-) production was significantly higher in the arteries from young in comparison to adult rats. Importantly, pan-inhibitor of NADPH oxidase VAS2870 (10 µM) reduced NADPH-induced O2•- production in arteries of young rats. Saphenous arteries of both young and adult rats demonstrated high levels of Nox2 and Nox4 mRNAs, while Nox1 and Nox3 mRNAs were not detected. The protein contents of NOX2 and NOX4 were significantly higher in arterial tissue of young compared to adult animals. Moreover, VAS2870 (10 µM) had no effect on methoxamine-induced contractile responses of adult arteries but decreased them significantly in young arteries; such effect of VAS2870 persisted after removal of the endothelium. Finally, NOX2 inhibitor GSK2795039 (10 µM), but not NOX1/4 inhibitor GKT137831 (10 µM) weakened methoxamine-induced contractile responses of arteries from young rats. Thus, ROS produced by NOX2 have a pronounced contractile influence in saphenous artery smooth muscle cells of young, but not adult rats, which is associated with the increased vascular content of NOX2 protein at this age.

Perinatal hypoxia weakens anticontractile influence of NO in rat arteries during early postnatal period.

BACKGROUND: Perinatal hypoxia affects a lot of neonates worldwide every year, however its effects on the functioning of systemic circulation are not clear yet. We aimed at investigation the effects of perinatal hypoxia on the second day of life on the functioning of the rat systemic vasculature in early postnatal period. METHODS: 2-day-old male rat pups were exposed to normobaric hypoxia (8% O2, 92% N2) for 2 hours. At the 11-14 days cutaneous (saphenous) arteries were isolated and studied by wire myography and Western blotting. RESULTS: Hypoxia weakened the contribution of anticontractile influence of NO, but did not affect the contribution of Rho-kinase or Kv7 channels to the contraction to α1-adrenergic agonist methoxamine. The content of eNOS and protein kinase G were not altered by hypoxic conditions. CONCLUSION: Perinatal hypoxia in rats at the second day of life leads to the decrease of anticontractile effect of NO in the systemic arteries in early postnatal ontogenesis (at the age of 11-14 days). Decreased anticontractile effect of NO can be the reason for insufficient blood supply and represent a risk factor for the development of cardiovascular disorders. IMPACT: The mechanisms of perinatal hypoxia influences on systemic circulation are almost unknown. We have shown that perinatal hypoxia weakens anticontractile influence of nitric oxide in early postnatal period. The influence of perinatal hypoxia on systemic circulation should be taken into account during treatment of newborns suffered from the lack of oxygen.

Voluntary wheel exercise training affects locomotor muscle, but not the diaphragm in the rat.

Introduction: Functional tests and training regimens intensity-controlled by an individual are used in sport practice, clinical rehabilitation, and space medicine. The model of voluntary wheel running in rats can be used to explore molecular mechanisms of such training regimens in humans. Respiratory and locomotor muscles demonstrate diverse adaptations to treadmill exercise, but the effects of voluntary exercise training on these muscle types have not been compared yet. Therefore, this work aimed at the effects of voluntary ET on rat triceps brachii and diaphragm muscles with special attention to reactive oxygen species, which regulate muscle plasticity during exercise. Methods: Male Wistar rats were distributed into exercise trained (ET) and sedentary (Sed) groups. ET group had free access to running wheels, running activity was continuously recorded and analyzed using the original hardware/software complex. After 8 weeks, muscle protein contents were studied using Western blotting. Results: ET rats had increased heart ventricular weights but decreased visceral/epididymal fat weights and blood triglyceride level compared to Sed. The training did not change corticosterone, testosterone, and thyroid hormone levels, but decreased TBARS content in the blood. ET rats demonstrated higher contents of OXPHOS complexes in the triceps brachii muscle, but not in the diaphragm. The content of SOD2 increased, and the contents of NOX2 and SOD3 decreased in the triceps brachii muscle of ET rats, while there were no such changes in the diaphragm. Conclusion: Voluntary wheel running in rats is intensive enough to govern specific adaptations of muscle fibers in locomotor, but not respiratory muscle.

TWIK-Related Acid-Sensitive Potassium Channels (TASK-1) Emerge as Contributors to Tone Regulation in Renal Arteries at Alkaline pH.

Aim: TASK-1 channels are established regulators of pulmonary artery tone but their contribution to the regulation of vascular tone in systemic arteries is poorly understood. We tested the hypothesis that TASK-1 channel functional impact differs among systemic vascular beds, that this is associated with differences in their expression and may increase with alkalization of the extracellular environment. Therefore, we evaluated the expression level of TASK-1 channels and their vasomotor role in mesenteric and renal arteries. Methods: Pulmonary, mesenteric and renal arteries from male Wistar rats were used for TASK-1 channel mRNA (qPCR) and protein content (Western blotting) measurements. The functional role of TASK-1 channels was studied by wire myography using the TASK-1 channel blocker AVE1231. In some experiments, the endothelium was removed with a rat whisker. Results: Expression levels of both mRNA and protein of the TASK-1 channel pore-forming subunit were highest in pulmonary arteries, lowest in mesenteric arteries and had an intermediate value in renal arteries. Blockade of TASK-1 channels by 1 µM AVE1231 increased U46619-induced contractile responses of pulmonary arteries but did not affect basal tone and contractile responses to methoxamine of mesenteric and renal arteries at physiological extracellular pH (pHo = 7.41). At alkaline extracellular pH = 7.75 (increase of NaHCO3 to 52 mM) AVE1231 evoked the development of basal tone and increased contractile responses to low concentrations of methoxamine in renal but not mesenteric arteries. This effect was independent of the endothelium. Conclusion: In the rat systemic circulation, TASK-1 channels are abundant in renal arteries and have an anticontractile function under conditions of extracellular alkalosis.

The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis.

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.

Region-specific effects of antenatal/early postnatal hypothyroidism on endothelial NO-pathway activity in systemic circulation.

BACKGROUND: Antenatal/early postnatal hypothyroidism weakens NO-mediated anticontractile influence of endothelium in coronary arteries of adult rats, but it remains unclear whether this occurs in other vascular regions. We hypothesized that developmental thyroid deficiency is followed by region-specific changes in the endothelial NO-pathway activity in systemic vasculature. To explore this, we estimated the effects of antenatal/early postnatal hypothyroidism on NO-pathway activity and its potential local control mechanisms in rat mesenteric and skeletal muscle (sural) arteries. METHODS: Dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%) during pregnancy and 2 weeks postpartum; control (CON) females received PTU-free water. Adult offspring (10-12-weeks) arteries were studied by wire myography, qPCR, and Western blotting. RESULTS: Endothelium removal or inhibition of NO-synthase with L-NNA augmented contractile responses to α1-adrenoceptor agonist methoxamine. In PTU compared to CON group, these effects were stronger in sural arteries, but did not differ in mesenteric arteries. The responses of both arteries to NO-donor DEA/NO were similar in CON and PTU rats. mRNA contents of deiodinase 2 and thyroid hormone receptor α were similar in mesenteric arteries of two groups but were elevated in sural arteries of PTU group compared to CON. The abundance of eNOS protein was higher in sural arteries of PTU compared to CON rats. CONCLUSION: Antenatal/early postnatal hypothyroidism is followed by an increase in NO-mediated anticontractile influence in sural, but not in mesenteric arteries of adult animals. The diversity of hypothyroidism effects may be due to different alterations of local T3 synthesis/reception in different vascular beds.

Intrauterine L-NAME Exposure Weakens the Development of Sympathetic Innervation and Induces the Remodeling of Arterial Vessels in Two-Week-Old Rats.

Nitric oxide (NO) has been shown to stimulate differentiation and increase the survival of ganglionic sympathetic neurons. The proportion of neuronal NOS-immunoreactive sympathetic preganglionic neurons is particularly high in newborn rats and decreases with maturation. However, the role of NO in the development of vascular sympathetic innervation has never been studied before. We tested the hypothesis that intrauterine NO deficiency weakened the development of vascular sympathetic innervation and thereby changed the contractility of peripheral arteries and blood pressure level in two-week-old offspring. Pregnant rats consumed NOS inhibitor L-NAME (250 mg/L in drinking water) from gestational day 10 until delivery. Pups in the L-NAME group had a reduced body weight and blood level of NO metabolites at 1-2 postnatal days. Saphenous arteries from two-week-old L-NAME offspring demonstrated a lower density of sympathetic innervation, a smaller inner diameter, reduced maximal active force and decreased α-actin/ß-actin mRNA expression ratio compared to the controls. Importantly, pups in the L-NAME group exhibited decreased blood pressure levels before, but not after, ganglionic blockade with chlorisondamine. In conclusion, intrauterine L-NAME exposure is followed by the impaired development of the sympathetic nervous system in early postnatal life, which is accompanied by the structural and functional remodeling of arterial blood vessels.

Intrauterine Nitric Oxide Deficiency Weakens Differentiation of Vascular Smooth Muscle in Newborn Rats.

Nitric oxide (NO) deficiency during pregnancy is a key reason for preeclampsia development. Besides its important vasomotor role, NO is shown to regulate the cell transcriptome. However, the role of NO in transcriptional regulation of developing smooth muscle has never been studied before. We hypothesized that in early ontogeny, NO is important for the regulation of arterial smooth muscle-specific genes expression. Pregnant rats consumed NO-synthase inhibitor L-NAME (500 mg/L in drinking water) from gestational day 10 till delivery, which led to an increase in blood pressure, a key manifestation of preeclampsia. L-NAME reduced blood concentrations of NO metabolites in dams and their newborn pups, as well as relaxations of pup aortic rings to acetylcholine. Using qPCR, we demonstrated reduced abundances of the smooth muscle-specific myosin heavy chain isoform, α-actin, SM22α, and L-type Ca2+-channel mRNAs in the aorta of newborn pups from the L-NAME group compared to control pups. To conclude, the intrauterine NO deficiency weakens gene expression specific for a contractile phenotype of arterial smooth muscle in newborn offspring.

Intrauterine growth restriction weakens anticontractile influence of NO in coronary arteries of adult rats.

Intrauterine growth restriction (IUGR) is one of the most common pathologies of pregnancy. The cardiovascular consequences of IUGR do not disappear in adulthood and can manifest themselves in pathological alterations of vasomotor control. The hypothesis was tested that IUGR weakens anticontractile influence of NO and augments procontractile influence of Rho-kinase in arteries of adult offspring. To model IUGR in the rat, dams were 50% food restricted starting from the gestational day 11 till delivery. Mesenteric and coronary arteries of male offspring were studied at the age of 3 months using wire myography, qPCR, and Western blotting. Contractile responses of mesenteric arteries to α1-adrenoceptor agonist methoxamine as well as influences of NO and Rho-kinase did not differ between control and IUGR rats. However, coronary arteries of IUGR rats demonstrated elevated contraction to thromboxane A2 receptor agonist U46619 due to weakened anticontractile influence of NO and enhanced role of Rho-kinase in the endothelium. This was accompanied by reduced abundance of SODI protein and elevated content of RhoA protein in coronary arteries of IUGR rats. IUGR considerably changes the regulation of coronary vascular tone in adulthood and, therefore, can serve as a risk factor for the development of cardiac disorders.

Remodeling of Arterial Tone Regulation in Postnatal Development: Focus on Smooth Muscle Cell Potassium Channels.

Maturation of the cardiovascular system is associated with crucial structural and functional remodeling. Thickening of the arterial wall, maturation of the sympathetic innervation, and switching of the mechanisms of arterial contraction from calcium-independent to calcium-dependent occur during postnatal development. All these processes promote an almost doubling of blood pressure from the moment of birth to reaching adulthood. This review focuses on the developmental alterations of potassium channels functioning as key smooth muscle membrane potential determinants and, consequently, vascular tone regulators. We present evidence that the pattern of potassium channel contribution to vascular control changes from Kir2, Kv1, Kv7 and TASK-1 channels to BKCa channels with maturation. The differences in the contribution of potassium channels to vasomotor tone at different stages of postnatal life should be considered in treatment strategies of cardiovascular diseases associated with potassium channel malfunction.

The susceptibility of the rat pulmonary and caval vein myocardium to the catecholamine-induced ectopy changes oppositely in postnatal development.

KEY POINTS: The developmental changes of the caval (SVC) and pulmonary vein (PV) myocardium electrophysiology are traced throughout postnatal ontogenesis. The myocardium in SVC as well as in PV demonstrate age-dependent differences in the ability to maintain resting membrane potential, to manifest automaticity in a form of ectopic action potentials in basal condition and in responses to the adrenergic stimulation. Electrophysiological characteristics of two distinct types of thoracic vein myocardium change in an opposite manner during early postnatal ontogenesis with increased proarrhythmicity of pulmonary and decreased automaticity in caval veins. Predisposition of PV cardiac tissue to proarrhythmycity develops during ontogenesis in time correlation with the establishment of sympathetic innervation of the tissue. The electrophysiological properties of caval vein cardiac tissue shift from a pacemaker-like phenotype to atrial phenotype in accompaniment with sympathetic nerve growth and adrenergic receptor expression changes. ABSTRACT: The thoracic vein myocardium is considered as a main source for atrial fibrillation initiation due to its high susceptibility to ectopic activity. The mechanism by which and when pulmonary (PV) and superior vena cava (SVC) became proarrhythmic during postnatal ontogenesis is still unknown. In this study, we traced postnatal changes of electrophysiology in a correlation with the sympathetic innervation and adrenergic receptor distribution to reveal developmental differences in proarrhythmicity occurrence in PV and SVC myocardium. A standard microelectrode technique was used to assess the changes in ability to maintain resting membrane potential (RMP), generate spontaneous action potentials (SAP) and adrenergically induced ectopy in multicellular SVC and PV preparations of rats of different postnatal ages. Immunofluorescence imaging was used to trace postnatal changes in sympathetic innervation, ß1- and α1A-adrenergic receptor (AR) distribution. We revealed that the ability to generate SAP and susceptibility to adrenergic stimulation changes during postnatal ontogenesis in an opposite manner in PV and SVC myocardium. While SAP occurrence decreases with age in SVC myocardium, it significantly increases in PV cardiac tissue. PV myocardium starts to demonstrate RMP instability and proarrhythmic activity from the 14th day of postnatal life which correlates with the appearance of the sympathetic innervation of the thoracic veins. In addition, postnatal attenuation of SVC myocardium automaticity occurs concomitantly with sympathetic innervation establishment and increase in ß1-ARs, but not α1A-AR levels. Our results support the contention that SVC and PV myocardium electrophysiology change during postnatal development, resulting in higher PV proarrhythmicity in adults.

Trophic sympathetic influence weakens pro-contractile role of Cl- channels in rat arteries during postnatal maturation.

Membrane transporters and their functional contribution in vasculature change during early postnatal development. Here we tested the hypothesis that the contribution of Cl- channels to arterial contraction declines during early postnatal development and this decline is associated with the trophic sympathetic influence. Endothelium-denuded saphenous arteries from 1- to 2-week-old and 2- to 3-month-old male rats were used. Arterial contraction was assessed in the isometric myograph, in some experiments combined with measurements of membrane potential. mRNA and protein levels were determined by qPCR and Western blot. Sympathectomy was performed by treatment with guanethidine from the first postnatal day until 8-9-week age. Cl- substitution in the solution as well as Cl--channel blockers (MONNA, DIDS) had larger suppressive effect on the methoxamine-induced arterial contraction and methoxamine-induced depolarization of smooth muscle cells in 1- to 2-week-old compared to 2- to 3-month-old rats. Vasculature of younger group demonstrated elevated expression levels of TMEM16A and bestrophin 3. Chronic sympathectomy increased Cl- contribution to arterial contraction in 2-month-old rats that was associated with an increased TMEM16A expression level. Our study demonstrates that contribution of Cl- channels to agonist-induced arterial contraction and depolarization decreases during postnatal development. This postnatal decline is associated with sympathetic nerves development.

TASK-1 channel blockade by AVE1231 increases vasocontractile responses and BP in 1- to 2-week-old but not adult rats.

BACKGROUND AND PURPOSE: The vasomotor role of K2P potassium channels during early postnatal development has never been investigated. We tested the hypothesis that TASK-1 channel (K2P family member) contribution to arterial vascular tone and BP is higher in the early postnatal period than in adulthood. EXPERIMENTAL APPROACH: We studied 10- to 15-day-old ("young") and 2- to 3-month-old ("adult") male rats performing digital PCR (dPCR) (using endothelium-intact saphenous arteries), isometric myography, sharp microelectrode technique, quantitative PCR (qPCR) and Western blotting (using endothelium-denuded saphenous arteries), and arterial pressure measurements under urethane anaesthesia. KEY RESULTS: We found mRNA of Kcnk1-Kcnk7, Kcnk12, and Kcnk13 genes to be expressed in rat saphenous artery, and Kcnk3 (TASK-1) and Kcnk6 (TWIK-2) were most abundant in both age groups. The TASK-1 channel blocker AVE1231 (1 µmol·L-1 ) prominently depolarized arterial smooth muscle and increased basal tone level and contractile responses to methoxamine of arteries from young rats but had almost no effect in adult rats. The level of TASK-1 mRNA and protein expression was higher in arteries from young compared with adult rats. Importantly, intravenous administration of AVE1231 (4 mg·kg-1 ) had no effect on mean arterial pressure in adult rats but prominently raised it in young rats. CONCLUSION AND IMPLICATIONS: We showed that TASK-1 channels are important for negative feedback regulation of vasocontraction in young but not adult rats. The influence of TASK-1 channels most likely contributes to low BP level at perinatal age.

Negative feedback regulation of vasocontraction by potassium channels in 10- to 15-day-old rats: Dominating role of Kv 7 channels.

AIM: Potassium channels are key regulators of smooth muscle membrane potential and arterial tone. However, the roles of potassium channels in vascular tone regulation in the systemic circulation during early postnatal development are poorly understood. Therefore, this study tested the hypothesis that the negative feedback regulation of vasocontraction by potassium channels changes during maturation. METHODS: Experiments were performed on endothelium-denuded saphenous arteries from 10- to 15-day-old and 2- to 3-month-old male rats. Isometric force and membrane potential were recorded using wire myography and the sharp microelectrode technique respectively; mRNA and protein contents were determined by qPCR and Western blotting. RESULTS: The effects of Kv 1, Kir and Kv 7 channel blockers (DPO-1, BaCl2 , XE991) on methoxamine-induced contraction were larger in arteries of 10- to 15-day-old compared to 2- to 3-month-old animals. In contrast, the BKCa channel blocker iberiotoxin had a stronger influence in 2- to 3- month-old rats. The effects of KATP and Kv 2 channel blockers (glibenclamide, stromatoxin) were not pronounced at both ages. The larger influence of Kv 7 and Kir channel blockade on arterial contraction in 10- to 15-day-old rats was associated with more prominent smooth muscle depolarization. The developmental alterations in potassium channel functioning were generally consistent with their mRNA and protein expression levels in arterial smooth muscle. CONCLUSION: The negative feedback regulation of vasocontraction by potassium channels varies during maturation depending on the channel type. A dominating contribution of Kv 7 channels to the regulation of basal tone and agonist-induced contraction was observed in arteries of 10- to 15-day-old animals.

Antenatal/early postnatal hypothyroidism increases the contribution of Rho-kinase to contractile responses of mesenteric and skeletal muscle arteries in adult rats.

BACKGROUND: Maternal thyroid deficiency can increase Rho-kinase procontractile influence in arteries of 2-week-old progeny. Here we hypothesized that augmented role of Rho-kinase persists in arteries from adult progeny of hypothyroid rats. METHODS: Dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%) during pregnancy and 2 weeks postpartum; control (CON) females received PTU-free water. At the age of 10-12-weeks, serum T3/T4 levels did not differ between PTU and CON male offspring. Cutaneous (saphenous), mesenteric, and skeletal muscle (sural) arteries were studied by wire myography, qPCR, and Western blotting. RESULTS: Saphenous arteries of PTU and CON groups showed similar responses to α1-adrenoceptor agonist methoxamine and were equally suppressed by Rho-kinase inhibitor Y27632. Responses of mesenteric arteries also did not differ between PTU and CON, but the effects of Y27632 were more prominent in the PTU group. Sural arteries of PTU rats compared to CON demonstrated augmented responses to methoxamine, increased RhoA mRNA contents and higher levels of MYPT1 phosphorylation at Thr855. Intergroup differences in contractile responses and phospho-MYPT1-Thr855 were eliminated by Y27632. CONCLUSION: Rho-kinase contribution to contractile responses of mesenteric and especially sural arteries is augmented in adult PTU rats. Therefore, maternal thyroid deficiency may have long-term detrimental consequences for vasculature in adult offspring.

Antenatal/early postnatal hypothyroidism alters arterial tone regulation in 2-week-old rats.

The mechanisms of vascular alterations resulting from early thyroid hormones deficiency are poorly understood. We tested the hypothesis that antenatal/early postnatal hypothyroidism would alter the activity of endothelial NO pathway and Rho-kinase pathway, which are specific for developing vasculature. Dams were treated with propylthiouracil (PTU, 7 ppm) in drinking water during gestation and 2 weeks after delivery, and their progeny had normal body weight but markedly reduced blood levels of thyroid hormones (ELISA). Small arteries from 2-week-old male pups were studied using wire myography, qPCR and Western blotting. Mesenteric arteries of PTU pups, compared to controls, demonstrated smaller maximum response to α1-adrenergic agonist methoxamine and reduced mRNA contents of smooth muscle differentiation markers α-actin and SERCA2A. Inhibition of basal NO synthesis by l-NNA led to tonic contraction of mesenteric arteries and augmented their contractile responses to methoxamine; both l-NNA effects were impaired in PTU pups. PTU pups demonstrated lower blood level of NO metabolites compared to control group (Griess reaction). Rho-kinase inhibitor Y27632 strongly reduced mesenteric arteries responses to methoxamine in PTU pups, that was accompanied by elevated Rho-kinase content in their arteries in comparison to control ones. Unlike mesenteric, saphenous arteries of PTU pups, compared to controls, had no changes in α-actin and SERCA2A contents and in responses to l-NNA and Y27632. In conclusion, thyroid hormones deficiency suppresses the anticontractile effect of NO and potentiates the procontractile Rho-kinase effects in mesenteric arteries of 2-week-old pups. Such alterations disturb perinatal cardiovascular homeostasis and might lead to cardiovascular pathologies in adulthood.

NO-mediated anticontractile effect of the endothelium is abolished in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism.

INTRODUCTION: Thyroid hormones are essential for proper development of many systems and organs, including circulatory system. Thyroid deficiency during pregnancy may affect the cardiovascular function in children early on and later in adulthood. However, long-term effects of early thyroid deficiency are poorly understood. We hypothesized that antenatal/early postnatal hypothyroidism will influence anticontractile effect of NO in coronary arteries of adult rats. DESIGN AND METHODS: To model antenatal/early postnatal hypothyroidism dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%, w/v) from the first day of pregnancy till 2 weeks after delivery. Control females were supplied with pure water. Their male offspring was grown up till the age of 10-12 weeks. Systolic blood pressure was measured using tail cuff method. Septal coronary arteries were isolated and studied in wire myograph. Blood serum thyroid hormones concentrations (ELISA) and NO metabolites level (Griess method) were evaluated. RESULTS: At the age of 10-12 weeks thyroid hormones, TSH concentrations, NO metabolites and systolic blood pressure level didn't differ between groups. Arterial responses to acetylcholine and exogenous NO-donor DEA/NO were similar in control and PTU groups. Along with that, in control rats endothelium denudation strongly potentiated basal tone of arteries and their contractile responses to thromboxane A2 receptor agonist U46619. The effects of endothelium denudation were absent in PTU rats indicating that anticontractile effect of endothelium is abolished in their arteries. Further, NO-synthase inhibitor L-NNA (100 µM) caused significant elevation of basal tone and increased U46619-induced contraction of endothelium-intact arteries only in control rats, while had no effect in PTU group. CONCLUSIONS: Our data demonstrate that NO-mediated anticontractile effect of endothelium is eliminated in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. Therefore, maternal thyroid hormones deficiency may have detrimental consequences in adult offspring including coronary circulation pathologies, despite normal blood levels of thyroid hormones.

Endothelial nitric oxide weakens arterial contractile responses and reduces blood pressure during early postnatal development in rats.

OBJECTIVE: During maturation the vascular system undergoes structural and functional remodeling. At the systemic level it results in a gradual increase of arterial blood pressure during postnatal ontogenesis. The mechanisms of maintaining the blood pressure at a comparatively low level during the early postnatal development are not completely understood. Recently we showed that the hindlimb arteries of young (1-2 wk-old) rats exhibited an enhanced endothelial NO-pathway activity, which weakened their contractile responsiveness compared to the arteries of adult rats. Here we tested the hypothesis that an increased tonic endothelial NO production can take place in the whole vascular system leading to a decreased level of systemic blood pressure in young rats. DESIGN AND METHODS: Segments of small mesenteric, saphenous, sural and intrarenal arteries were isolated from the young (2 wk-old), juvenile (4 wk-old) and adult (10-12 wk-old) male rats and tested in a wire isometric myograph. Anticontractile effect of NO was evaluated by the effects of NOS inhibitor L-NNA on both arterial spontaneous tone and constrictor responses to methoxamine (α1-adrenoceptor agonist). In addition, eNOS and arginase-2 mRNA expression in arterial preparations by qPCR and serum nitrite/nitrate levels by Griess reaction were estimated. Blood pressure with an intra-carotid artery catheter was measured in conscious rats. RESULTS: In all arteries of 2 wk rats except the renal ones, L-NNA exposure resulted in a considerable tonic contraction and a remarkable enhancement of contractile responses to methoxamine. The effect of L-NNA gradually decreased with age and by 10-12 weeks became very small in the mesenteric arteries and disappeared in the sural and saphenous arteries. Although no difference in eNOS mRNA expression was found, the content of arginase-2 mRNA was significantly lower in young rats compared to adults. Serum levels of NO metabolites were two-fold higher in 2 wk-old rats than in adult rats. Along with that, arterial blood pressure was by half lower but rose more prominently after administration of l-NAME in young rats than in adults. CONCLUSIONS: In young rats, tonic release of NO by the endothelium considerably weakens contractile responses of arteries supplying intestine, skin and skeletal muscles, which receive a high proportion of the cardiac output. Such anticontractile effect of NO can be an important mechanism responsible for the blood pressure reduction in immature circulatory system.