Background and Objective:
All three isoforms of nitric oxide (NO) synthase (NOS) are targets
for thyroid hormones in cardiovascular system. The aim of this study was to assess effects of hypoand 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, respectively. At 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 measured.
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 in the
heart and aorta of hyperthyroid rats were higher (56% and 40%) than controls. Compared to
controls, hypothyroid rats had lower levels of eNOS, iNOS, and nNOS in 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 ratio of eNOS/iNOS in aorta and heart; these changes
of NOS levels were associated with impaired cardiovascular function.