Evaluation of serum vascular smooth muscle tone regulators in patients with hypothyroidism and concomitant hypertension: A cross-sectional study

Abstract

Objective: Hypothyroidism is known to affect cardiovascular function through multiple mechanisms, yet the role of vascular smooth muscle tone regulators in early disease remains incompletely understood. This study evaluated serum levels of myosin light chain kinase, nitric oxide synthase, and calcitonin gene-related peptide in patients with hypothyroidism, with and without hypertension, compared to healthy controls.

Methods: A hospital-based cross-sectional study enrolled 90 participants from the Endocrinology Unit of Azadi Teaching Hospital between February and April 2024: 35 patients with hypothyroidism alone, 35 patients with hypothyroidism and hypertension, and 20 age-matched healthy controls. Thyroid function tests and parathyroid hormone were measured using automated analysers. Myosin light chain kinase, nitric oxide synthase, and calcitonin gene-related peptide were quantified by enzyme-linked immunosorbent assay. Group comparisons used Kruskal-Wallis ANOVA with Dunn's post-hoc test.

Results: Both patient groups showed significantly elevated TSH (8.26±3.81 and 10.44±4.38 vs 2.09±0.87 µIU/mL, p<0.001) and reduced T3 and T4 compared to controls (p<0.001). Parathyroid hormone was highest in the hypothyroidism-with-hypertension group (60.12±26.88 pg/mL). Nitric oxide synthase was reduced in both patient groups (8.25±5.64 and 9.17±6.07 vs 11.81±6.21 ng/mL, p=0.04). Calcitonin gene-related peptide was lower in hypothyroid patients with hypertension (153.81±61.35 vs 172.46±94.27 ng/mL, p=0.048). Myosin light chain kinase showed no significant differences between groups.

Conclusion: Hypothyroidism, particularly when accompanied by hypertension, is associated with reduced serum nitric oxide synthase and calcitonin gene-related peptide levels, suggesting impairment of endothelial and neurovascular vasodilatory pathways. These findings support further investigation of vascular biomarkers for cardiovascular risk assessment in hypothyroid patients.