Comparison of normal, hypodynamic, and hyperdynamic mouse hearts using isolated work-performing heart preparations

Area of Science:

• Cardiovascular Physiology
• Endocrinology
• Molecular Biology

Background:

• Genetic manipulation allows for the study of myocardial protein function in transgenic mice.
• Thyroid hormones are critical regulators of cardiac metabolism and contractility.

Purpose of the Study:

• To quantify myocardial performance in euthyroid, hypothyroid, and hyperthyroid mouse heart preparations.
• To assess the role of thyroid status and beta-adrenergic activity in cardiac function.

Main Methods:

• Utilized work-performing mouse heart preparations to measure indicators of systolic contraction and relaxation.
• Measured time to peak pressure (TPP), time to half-relaxation (RT1/2), and pressure derivatives (+/- dP/dt).
• Investigated the effects of isoproterenol and sotalol on cardiac contractility in hyperthyroid mice.

Main Results:

• Myocardial performance indicators were significantly elevated in hyperthyroid mice and reduced in hypothyroid mice compared to controls.
• Observed the characteristic alpha-->beta cardiac myosin heavy chain isoform transcript shift in hypothyroid mice.
• Beta-adrenergic activity accounted for only about 50% of the enhanced cardiac contractility in hyperthyroid mice.

Conclusions:

• Thyroid hormone status profoundly influences myocardial performance, affecting both contraction and relaxation.
• Hypothyroidism induces molecular changes in cardiac myosin, impacting contractility.
• Non-adrenergic mechanisms contribute significantly to the hyperthyroid-induced cardiac hyperactivity.