Cardiovascular problems in rabbits in reference to hypothyroidism - a four-year retrospective study.

Area of Science:

• Veterinary Cardiology
• Endocrinology
• Comparative Physiology

Background:

• Hypothyroidism in rabbits is characterized by impaired myocardial contractility and reduced ejection capacity due to thyroid hormone deficiency, particularly thyroxine (T4).
• Thyroxine (T4) is known to exert positive inotropic and chronotropic effects on the heart.

Purpose of the Study:

• To investigate the correlation between serum thyroxine (T4) concentration and cardiac systolic function, specifically fractional shortening, in hypothyroid rabbits.
• To determine if this correlation varies across different age groups, sexes, and sterilization statuses.

Main Methods:

• Echocardiography (2D imaging, M-mode, Doppler) was used to assess cardiac function (fractional shortening, heart rate, LA/Ao ratio).
• Serum T4 levels were measured in 41 rabbits (15 males, 26 females) with pre-existing reduced fractional shortening (<30%).
• Statistical analysis (Statistica 13.0) was employed to correlate T4 levels with echocardiographic parameters across various subgroups.

Main Results:

• A significant positive correlation was observed between serum T4 concentration and myocardial fractional shortening in hypothyroid rabbits.
• Positive correlations were also found between T4 levels and heart rate and the left-atrial to aortic ratio (LA/Ao).
• These correlations remained consistent across different age groups (young vs. older), sexes (male vs. female), and sterilization statuses (sterilized vs. non-sterilized).

Conclusions:

• Decreased serum T4 concentration is unequivocally linked to reduced cardiac systolic function (fractional shortening) in hypothyroid rabbits.
• Thyroxine plays a crucial role in maintaining normal cardiac contractility in rabbits.
• These findings highlight the importance of monitoring T4 levels in rabbits with cardiac dysfunction.