Changes in vascular reactivity induced by acute hyperthyroidism in isolated rat aortae

Area of Science:

• Cardiovascular Physiology
• Endocrinology
• Pharmacology

Background:

• Hyperthyroidism, an excess of thyroid hormones like thyroxine (T4), significantly impacts cardiovascular function.
• Early-stage alterations in vascular responsiveness are crucial for understanding disease progression and potential interventions.

Purpose of the Study:

• To investigate the early effects of induced hyperthyroidism on adrenergic and muscarinic receptor-mediated vascular responses.
• To determine the role of the nitric oxide (NO) system in these altered vascular responses.

Main Methods:

• Hyperthyroidism was induced in rats via L-thyroxine (T4) injections.
• Isometric tension measurements of isolated aortic ring preparations were used to assess vascular responses.
• The effects of norepinephrine (NE), acetylcholine (ACh), and sodium nitroprusside (SNP) were evaluated, along with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine (L-NOARG).

Main Results:

• T4 treatment led to significant hyperthyroid indicators including weight loss, tachycardia, cardiac hypertrophy, and elevated serum T4.
• Norepinephrine-induced contractions were suppressed in hyperthyroid rat aortas.
• Acetylcholine and sodium nitroprusside-induced relaxations were enhanced in hyperthyroid rat aortas.
• L-NOARG potentiated NE-induced contractions more significantly in T4-treated rats and abolished ACh-induced relaxation, while altering SNP-induced relaxation differently between control and T4 groups.
• Endothelial nitric oxide synthase (eNOS) protein levels remained unchanged.

Conclusions:

• Vascular responses are significantly altered at an early stage of hyperthyroidism.
• These alterations appear to be mediated by modifications within the nitric oxide system.
• The observed changes in vascular function are independent of alterations in the amount of endothelial nitric oxide synthase protein.