Efectos de la tiroxina y la triyodotironina en la vena safena humana

Resum

Clinical complications after coronary by-pass surgery in elderly patients with or without left ventricular failure, is the most important cause of its morbidity and mortality in which underlying hormonal alterations such as reduced levels of 3,3-triiodo-L-thyronine (T3) has been well established. As is the case of hypothyroid patients, there is a decrease of cardiac contractility and an increase of peripheral vascular resistance. Different studies have demonstrated the beneficial effect induced by T3 during the surgical period although the mechanisms involved on the human saphenous vein, used in coronary by-pass, are not well established. The purpose of our study was to investigate the response of the saphenous vein to thyroxine (T4) and T3. In this context, it is pertinent to study the role of the endothelial component, the release of nitric oxide (NO), as well as the other vaso-active substances such as prostacyclin or EDHF (Endothelium Dependent Hiperpolarizing Factor). In addition, the possible implication of Na+/K+-ATPase, K+-channels, AMPc and GMPc has also been investigated. In segments of human saphenous vein previously contracted with noradrenaline the administration of T3 or T4 (109 -106 M) induces a concentration-dependent relaxing effect independently of the presence or absence of endothelium, NO and prostacyclin as relaxation factors. The relaxation is accompanied by the increase of GMPc but not AMPc levels suggesting a pivotal role of the enzyme guanylate cyclase rather than adenyl cyclase in the relaxing mechanism induced by thyroid hormones. This relaxation induced by T3 is not modified by Ca2+-dependent K+ channel blockers discarding the role of a hyperpolarization effect. T3-induced effect is reduced in the presence of oabain, a Na+,K+-ATPase inhibitor, or in the presence of barium, an inwardly rectifying K+ channels blocker. The obtained results indicate that T3 has direct effects on the contractility of the human saphenous vein. The vaso-relaxing effects may be beneficial in the treatment of patients submitted to coronary by-pass surgery.