Impaired Endothelium-Dependent Vasodilatation in Subclinical Hypothyroidism: Beneficial Effect of Levothyroxine Therapy

Abstract

Subclinical hypothyroidism (sHT) is associated with enhanced cardiovascular risk. To test the hypothesis that patients with sHT are characterized by endothelial dysfunction and impaired nitric oxide (NO) availability, in 14 patients [serum cholesterol, 218 +/- 41 mg/dl (5.6 +/- 0.9 mM)] and 28 euthyroid subjects, subdivided into groups A and B [serum cholesterol, 170 +/- 19 mg/dl (4.4 +/- 0.5 mM) and 217 +/- 21 mg/dl (5.6 +/- 0.5 mM), respectively], we studied the forearm blood flow (strain-gauge plethysmography) response to intrabrachial acetylcholine, an endothelium-dependent vasodilator, at baseline and during infusion of N(G)-monomethyl-L-arginine (L-NMMA), a NO synthase inhibitor. Response to sodium nitroprusside and minimal forearm vascular resistances were also evaluated. In sHT patients, vasodilation to acetylcholine was reduced, compared with group B (+358 +/- 29% vs. +503 +/- 19%, P = 0.0003) and group A (663 +/- 65%, P = 0.02 vs. group B and P = 0.0002 vs. sHT). L-NMMA blunted the vasodilation to acetylcholine in groups A and B (49.1 +/- 6.3% and 42.7 +/- 5.5% maximal forearm blood flow reduction, respectively, P < 0.0001 vs. acetylcholine), whereas it was ineffective in sHT patients (12.8 +/- 2.5%). Response to sodium nitroprusside and minimal vascular resistances were similar. In sHT (n = 9) patients, 6 months of euthyroidism by levothyroxine replacement increased acetylcholine-vasodilation and restored L-NMMA inhibition. Patients with sHT are characterized by endothelial dysfunction resulting from a reduction in NO availability, an alteration partially independent of dyslipidemia and reversed by levothyroxine supplementation.

Evaluation of the respective influence of thyroid hormones and TSH on blood coagulation parameters after total thyroidectomy

“…in auto-immune hypothyroidism), the change in coagulation parameters could be more pronounced. Our findings demonstrate that thyroid hormone deficiency may be associated with significant alterations of hemostasis due to a decrease in VWF:Ag, VWF:CBA, and FVIII:C. Hypothyroidism (overt or subclinical) could also be associated with increased cardiovascular risk, although the mechanisms are not clearly defined (25)(26)(27). This association could be explained through the endothelial dysfunction described in hypothyroidism, which plays a major role in the development of atherosclerosis in addition to classical cardiovascular risk factors.…”

Association between Subclinical Hypothyroidism and Proliferative Diabetic Retinopathy in Type 2 Diabetic Patients: A Case-Control Study

“…SCH is associated with atherogenic lipid profile (Bindels et al 1999;Tsimihodimos et al 1999;Pirich et al 2000;Tzotzas et al 2000;Vierhapper et al 2000;Efstathiadou et al 2001;Meier et al 2001;Kanaya et al 2002;Caraccio et al 2002;Monzani et al 2004), impaired vascular function (Taddei et al 2003), impaired cardiac function, and increased risk for the development of atherosclerosis and myocardial dysfunction (Hak et al 2000;Biondi et al 2002). With respect to the metabolic syndrome, as might be expected, the prevalence of SCH is higher in patients with metabolic conditions than that in non-metabolic syndrome subjects (Uzunlulu et al 2007).…”

Science and education in XXI century. Vol. 5

“…По сравнению с контрольной груп-пой эндотелийзависимая вазодилатация была значительно снижена у пациентов группы СГТ. При этом введение LMMNA не оказывало дополнительного эф-фекта, что позволило сделать вывод об опосредованности эндотелиальной дис-функции дефектом синтеза NO [24].…”