Direct effects of triiodothyronine on human internal mammary artery and saphenous veins

Thyroxine Induces Acute Relaxation of Rat Skeletal Muscle Arteries via Integrin αvβ3, ERK1/2 and Integrin-Linked Kinase

Aim: Hyperthyroidism is associated with a decreased peripheral vascular resistance, which could be caused by the vasodilator genomic or non-genomic effects of thyroid hormones (TH). Non-genomic, or acute, effects develop within several minutes and involve a wide tissue-specific spectrum of molecular pathways poorly studied in vasculature. We aimed to investigate the mechanisms of acute effects of TH on rat skeletal muscle arteries.

Methods: Sural arteries from male Wistar rats were used for isometric force recording (wire myography) and phosphorylated protein content measurement (Western blotting).

Results: Both triiodothyronine (T3) and thyroxine (T4) reduced contractile response of sural arteries to α₁-adrenoceptor agonist methoxamine. The effect of T4 was more prominent than T3 and not affected by iopanoic acid, an inhibitor of deiodinase 2. Endothelium denudation abolished the effect of T3, but not T4. Integrin αvβ3 inhibitor tetrac abolished the effect of T4 in endothelium-denuded arteries. T4 weakened methoxamine-induced elevation of phospho-MLC2 (Ser19) content in arterial samples. The effect of T4 in endothelium-denuded arteries was abolished by inhibiting ERK1/2 activation with U0126 as well as by ILK inhibitor Cpd22 but persisted in the presence of Src- or Rho-kinase inhibitors (PP2 and Y27632, respectively).

Conclusion: Acute non-genomic relaxation of sural arteries induced by T3 is endothelium-dependent and that induced by T4 is endothelium-independent. The effect of T4 on α₁-adrenergic contraction is stronger compared to T3 and involves the suppression of extracellular matrix signaling via integrin αvβ3, ERK1/2 and ILK with subsequent decrease of MLC2 (Ser19) phosphorylation.

Endocrine mechanisms in the pathogenesis of primary varicosis

Introduction: Varicose veins affect up to 40 % of men and up to 51 % of women. The patho-physiology of primary varicosis (chronic venous insufficiency, CVI) is poorly understood. Here, the available data on possible endocrine mechanisms in healthy and varicose veins are reviewed.

Methods: An extensive literature search was conducted in PubMed using the following key words: Chronic venous insufficiency, CVI, chronic venous disease, CVD, varicosis, saphenous vein, pathogenesis, hormone.

Results: Several theories ranging from incompetence of the valves to functional, biological or morphologic changes in different layers of the vein wall have been proposed. However, an increasing body of evidence suggests that endocrine mechanisms might be involved in the pathogenesis of primary varicosis. In this respect a growing number of hormones (e.g. estrogen, progesterone, relaxin-2, and oxytocin) and their receptors have been linked to primary varicosis in experimental, pharmacological and histological studies.

Conclusion: In summary, endocrine-based mechanisms seem to play a role in the pathogenesis of primary varicosis. This opens up the perspective for pharmacological treatments targeting the various described endocrine regulatory networks.

The crosstalk between thyroid hormones and the Renin-Angiotensin System

Thyroid hormones (THs) exert multiple effects on the heart and vascular system. As a consequence, altered cardiovascular function observed in the thyroid diseases corresponds to one of the most important and clinically relevant aspects found in both hyperthyroidism and hypothyroidism. Besides THs' direct effects on the heart and vascular system, in the last three decades several studies have implicated the Renin-Angiotensin System (RAS) in some of the cardiovascular effects of THs, with this interaction suggesting that RAS may be an important mediator of THs actions. In the present review, we discuss the alterations in the circulating RAS, as well as modifications in cardiac and vascular RAS which are involved in the cardiovascular alterations found during the modulation of TH levels. In addition, considering the important role that both systems present during fetal and neonatal periods, we also review the interaction between THs and the RAS in the development of cardiovascular system. A greater understanding of the role of the RAS in hyperthyroidism and hypothyroidism, during early or adult life will presumably facilitate the evolution of newer, targeted therapies.

Airway epithelial-derived factor relaxes pulmonary vascular smooth muscle

The factors controlling the pulmonary vascular resistance under physiological conditions are poorly understood. We have previously reported on an apparent cross talk between the airway and adjacent pulmonary arterial bed where a factor likely derived from the bronchial epithelial cells reduced the magnitude of agonist-stimulated force in the vascular smooth muscle. The main purpose of this investigation was to evaluate whether bronchial epithelial cells release a pulmonary arterial smooth muscle relaxant factor. Conditioned media from SPOC-1 or BEAS-2B, a rat- and a human-derived bronchial epithelial cell line, respectively, were utilized. This media significantly relaxed precontracted adult but not fetal pulmonary arterial muscle in an oxygen tension-dependent manner. This response was mediated via soluble guanylate cyclase, involving AKT/PI3-kinase and neuronal nitric oxide synthase. Airway epithelial cell-conditioned media increased AKT phosphorylation in pulmonary smooth muscle cells (SMC) and reduced intracellular calcium change following ATP stimulation to a significantly greater extent than observed for bronchial SMC. The present data strongly support the evidence for bronchial epithelial cells releasing a stable and soluble factor capable of inducing pulmonary arterial SMC relaxation. We speculate that under physiological conditions, the maintenance of a low pulmonary vascular resistance, postnatally, is in part modulated by the airway epithelium.

Effects of stretch or distention on phenylephrine-induced constriction of human coronary artery bypass grafts

OBJECTIVE

To determine the effects of grafting saphenous veins into the arterial circulation and to compare the responsiveness of saphenous veins and mammary arteries to vasoconstrictors (phenylephrine or potassium) and a vasodilator (the calcium antagonist isradipine).

DESIGN

Prospective, controlled, in vitro study.

SETTING

Laboratory facility in a university teaching hospital.

PARTICIPANTS

Small excess segments of internal mammary arteries or saphenous veins obtained from patients undergoing coronary artery bypass graft surgery.

INTERVENTIONS

Vessel segments were cut into rings to measure isometric tension development in isolated tissue chambers. The law of LaPlace for a cylinder was applied to determine tensions in vitro corresponding with arterial or venous tensions in vivo or distending pressures ex vivo.

MEASUREMENTS AND MAIN RESULTS

Stretching saphenous vein rings from venous to arterial tensions reduced maximal phenylephrine-induced constriction but did not alter their dose response to phenylephrine, potassium, or isradipine. At arterial tensions, potassium, but not phenylephrine, was more potent in constricting mammary artery than saphenous vein; isradipine was more potent as a vasodilator of potassium-constricted mammary artery than saphenous vein. Maximal phenylephrine-induced or potassium-induced constriction was no different for either vessel at arterial tensions; however, prior distention of veins to tensions corresponding with pressures of 200 or 300 mmHg significantly (p < 0.01, Dunnett's test) reduced subsequent constriction.

CONCLUSION

Phenylephrine may be more likely to constrict native internal mammary arteries than distended autogenous saphenous vein grafts in vivo because high-pressure distention of veins markedly inhibits their vasoreactivity.