Modulation of liver mitochondrial NOS is implicated in thyroid-dependent regulation of O2 uptake

1 Laboratory of Oxygen Metabolism and 2 Nuclear Medicine Center, University Hospital, University of Buenos Aires, 1120 Buenos Aires, Argentina Changes in O 2 uptake at different thyroid status have been explained on the basis of the modulation of mitochondrial enzymes and membrane biophysical properties. Regarding the nitric oxide (NO) effects, we tested whether liver mitochondrial nitric oxide synthase (mtNOS) participates in the modulation of O 2 uptake in thyroid disorders. Wistar rats were inoculated with 400 µCi 131 I (hypothyroid group), 20 µg thyroxine (T 4 )/100 g body wt administered daily for 2 wk (hyperthyroid group) or vehicle (control). Basal metabolic rate, mitochondrial function, and mtNOS activity were analyzed. Systemic and liver mitochondrial O 2 uptake and cytochrome oxidase activity were lower in hypothyroid rats with respect to controls; mitochondrial parameters were further decreased by L -arginine ( 42 and 34%, P