Effects of induced hyperthyroidism in normal and cardiomyopathic hamsters

Area of Science:

• Cardiology
• Endocrinology
• Molecular Biology

Background:

• Thyroid hormones (TH) are known to influence cardiac function.
• While beneficial in some contexts, excess TH can lead to heart failure in humans, but this effect is less clear in animal models.
• The distinct effects of TH on normal versus cardiomyopathic hearts require further investigation.

Purpose of the Study:

• To investigate the impact of prolonged hyperthyroidism on cardiac function.
• To analyze chamber and cellular remodeling in response to excess TH.
• To examine protein expression changes in normal and cardiomyopathic hearts under hyperthyroid conditions.

Main Methods:

• Induction of hyperthyroidism in normal (BIO F1B) and cardiomyopathic (BIO TO2) hamsters.
• Assessment of cardiac hemodynamics, echocardiography, myocyte length, histology, and protein expression after 10 days and 2 months of TH treatment.
• Comparison of treated hamsters with untreated controls.

Main Results:

• Prolonged hyperthyroidism induced dilated heart failure in normal hamsters, characterized by increased chamber diameters and reduced ejection fraction.
• In cardiomyopathic hamsters, excess TH did not adversely affect chamber function or dimensions, but increased myocyte length and improved myocardial viability.
• Changes in myosin heavy chain isoform expression (decreased beta-myosin, increased alpha-myosin in normal hearts) were observed, but did not necessarily correlate with improved cardiac function.

Conclusions:

• Excess thyroid hormones can precipitate heart failure in normal hearts, mirroring human responses.
• Reversal of myosin heavy chain expression does not guarantee improved cardiac function.
• While excess TH induced cellular remodeling, it did not impair overall cardiac chamber function in cardiomyopathic hamsters.