Selective decrease of Na⁺/K⁺-ATPase activity in the brain of hypothyroid rats

The present work was performed in order to know if mild hypothyroidism in rats modifies the activity of the Na⁺/K⁺-ATPase in different regions of the brain. Male Wistar rats (300-350 g) were randomly divided into three groups: 1) control group (n=8) drank tap water. 2) hypothyroid group (n=8) treated with 60 mg/kg of methimazole in drinking water; and 3) replaced group (n=8) treated with 60 mg/kg of methimazole plus 35 μg/kg of thyroid hormone (T₃) in drinking water. After four weeks of treatment, the rats of all groups were sacrificed by decapitation. The cortex, amygdala, hippocampus and cerebellum were dissected and frozen at -70°C until assay. For enzymatic assay, the tissues were homogenized. The Na⁺/K⁺-ATPase activity was determined by quantifying inorganic phosphate after the samples were incubated with ATP in the presence and absence of 1 mM ouabain. The Na⁺/K⁺-ATPase activity is expressed as μmoles Pi/hr/mg protein. The results showed that the Na ⁺/K⁺-ATPase activity in the cortex, amygdala and hippocampus, but not in cerebellum, was lower in hypothyroid group than in control group (p<0.05). The co-administration of methimazole and T ₃ avoided the decrease of Na⁺/K⁺-ATPase activity, except in amygdala. According to the results obtained we concluded that methimazole treatment decreased the Na⁺/K⁺-ATPase activity in the brain's regions which are related to seizures onset. That decrement in enzyme activity was avoided with the co-administration of thyroid hormone.