BackgroundHyperthyroidism (Hy) exerts a broad range of influences on a variety of
physiological parameters. Its disruptive effect on cardiovascular system is one of
its most remarkable impacts. Moreover, Hy has been clinically associated with
stress - induced hyperactivation of the hypothalamic-pituitary-adrenal axis.ObjectiveEvaluate the impact of short-term Hy on cardiac performance and adrenal activity
of rats.MethodsInduction of Hy in Wistar rats through injections of T3 (150
µg/kg) for 10 days (hyperthyroid group - HG) or vehicle (control
group). The cardiovascular performance was evaluated by: echocardiography (ECHO);
heart weight/body weight (mg/gr) ratio; contractility of isolated papillary
muscles (IPM) and direct measurement of blood pressures. Adrenal activity was
evaluated by adrenal weight/body weight (mg/gr) ratio and 24-hour fecal
corticosterone (FC) levels on the, 5th and 10th days of T3
treatment.ResultsIn HG, the ECHO showed reduction of the End Systolic and End Diastolic Volumes,
Ejection, Total Diastolic and Isovolumic Relaxation Times, Diastolic and Systolic
Areas and E/A ratio. Heart Rate, Ejection Fraction and Cardiac Output increased.
The heart weight/body weight ratio was higher. Similarly, in IPM, the maximum rate
of force decay during relaxation was higher in all extracellular calcium
concentrations. Systolic blood pressure (SBP) levels were higher. (p ≤ 0.05). On
the other hand, there was no difference in the adrenal weight/body weight ratio or
in the 24-hour FC levels.ConclusionsHy induces positive inotropic, chronotropic and lusitropic effects on the heart by
direct effects of T3 and increases SBP. Those alterations are not correlated with
changes in the adrenal activity.