Background and Objective: All three isoforms of nitric oxide (NO) synthase (NOS) are
targets for thyroid hormones in the cardiovascular system. The aim of this study was to assess the effects
of hypo- and hyperthyroidism on inducible (iNOS), endothelial (eNOS), and neural (nNOS) NOS
levels in aorta and heart tissues of male rats.
Methods: Rats were divided into control, hypothyroid, and hyperthyroid groups; hypo- and hyperthyroidism
were induced by adding propylthiouracil (500 mg/L) and L-thyroxine (12 mg/L) to drinking
water for a period of 21 days. On day 21, systolic blood pressure, heart rate, left ventricular developed
pressure (LVDP), peak rate of positive and negative (±dp/dt) changes in left ventricular pressure as
well as NO metabolites (NOx) and iNOS, eNOS, and nNOS protein levels in aorta and heart, were all
Results: Compared to controls, LVDP and ±dp/dt were lower in both hypo- and hyperthyroid rats.
Compared to controls, heart rate and systolic blood pressure were lower in hypothyroid and higher in
hyperthyroid rats. NOx levels in the heart of hypothyroid rats were lower (53%), whereas that in hyperthyroid
rats were higher (56% and 40%) than controls. Compared to controls, hypothyroid rats had
lower levels of eNOS, iNOS, and nNOS in the aorta (16%, 34%, and 15%, respectively) and lower
iNOS and higher nNOS in heart tissue (27% and 46%). In hyperthyroid rats, eNOS levels were lower
(54% and 30%) and iNOS were higher (63%, and 35%) in the aorta and heart while nNOS was lower
in the aorta (18%).
Conclusion: Hypothyroidism increased while hyperthyroidism decreased the ratio of eNOS/iNOS in
aorta and heart; these changes of NOS levels were associated with impaired cardiovascular function.