Abstract Body (Do not enter title and authors here): Background: Women’s health is underfunded, and women are underrepresented in heart failure research, leading to knowledge gaps. Literature supports that a decrease in thyroid hormones and estrogen are correlated to higher risk of cardiovascular disease. We created an endocrine (triiodothyronine (T3) and 3,3’-Diido-L-thyronine (3,3’-T2) and estradiol (E2) deficient rodent heart failure model to evaluate the role of these hormones in cardiac function and recovery.

Hypothesis: Hormone loss will affect cardiac function and impair recovery after a myocardial infarction (MI) while reintroduction of these hormones will improve overall health.

Methods: We conducted a study with hypothyroid (1 mg/ml propylthiouracil) female Sprague Dawley (190-225g) rats. We compared pre- and post-menopausal (ovariectomized (OVX)) animals as well as animals with the introduction of exogenous E2. All rats underwent MI through left anterior descending (LAD) artery ligation and were divided into groups (n=10) for hormone replacement therapy (T3, 3,3’-T2, and/or E2) or vehicle introduced via their drinking water. Over 9 weeks, we monitored weight, blood pressure, hormone levels, and body temperature. Echocardiograms and electrocardiograms were performed pre- and post-MI. Rat hearts and thyroids were harvested, weighed, and stained to assess for hypertrophy.

Results: Hypothyroidism showed a significant (***P<0.001) reduction in pulse and cardiac function compared to euthyroid rats. The euthyroid T3 treatment resulted in significantly lower (**P<0.01) left ventricular ejection fraction (LVEF) % than hypothyroid T3 treatment, which resulted in a higher LVEF %. Post-MI introduction of exogenous T3 significantly (****P<0.0001) reduced heart weight for hypothyroid rats compared to euthyroid rats (Fig. 1).

Conclusion: Our study demonstrates replacement of exogenous hormones (both endocrine and sex hormones) after a cardiac event can improve overall health and recovery. Further studies are still needed to determine administration type, dosage, and timing to enhance cardiac repair. Administration of exogenous hormones in individuals where endogenous production has been impaired can be used productively for heart failure treatment.