Thyroid hormones increase Na+–Pi co-transport activity in intestinal brush border membrane: Role of membrane lipid composition and fluidity

Reduced parietooccipital white matter glutamine measured by proton magnetic resonance spectroscopy in treated graves' disease patients

CONTEXT

Graves' disease is an autoimmune disease of the thyroid gland. Patients often have affective and cognitive complaints, whether these disappear after treatment remains disputed.

OBJECTIVE

Our objective was to evaluate cerebral biochemistry in acute and treated Graves' disease.

DESIGN

We conducted a prospective study, investigating volunteers once and patients before and 1 yr after treatment.

SETTING

The study was performed at a radiology department, a memory disorder clinic, and two endocrinology clinics.

PATIENTS AND OTHER PARTICIPANTS

Of 53 consecutively referred, newly diagnosed, and untreated patients with Graves' thyrotoxicosis, 27 patients (34 +/- 8 yr) and 33 matched volunteers were included.

INTERVENTIONS

Patients were treated with thionamide.

MAIN OUTCOME MEASURES

We assessed brain metabolite concentrations.

METHODS

Proton magnetic resonance spectroscopy of the brain and a battery of biochemical, affective, and cognitive tests were used.

RESULTS

Previously reported findings of reduced choline and myo-inositol in acute Graves' disease were confirmed and reversibility was demonstrated. Parieto-occipital white matter glutamine was and remained significantly reduced (P < 0.01). Acute phase parieto-occipital white matter total choline correlated significantly (r = -0.57; P < 0.01) with impaired thyroid function. Pretreatment total T(3) predicted posttreatment occipital gray matter glutamine (r = -0.52; P < 0.01). Occipital gray matter total choline (r = -0.53; P < 0.01) and parietooccipital white matter glutamate (r = -0.54; P < 0.01) correlated with initial values of selected attention and concentration cognitive scores and predicted them at follow-up.

CONCLUSIONS

The persistent reduction of glutamine in white matter, the decreasing glutamate in occipital gray matter, and the correlation with severity of the initial disease as well as with attention and concentration cognitive scores indicated that there was a persistent and possibly progressive disturbance of the glutamate glutamine cycling in Graves' disease.

Effect of thyroid hormone on the distribution and activity of Na, K-ATPase in ventricular myocardium

Employing detergent-free sucrose-density gradient fractionation method we isolated cholesterol-rich lighter membrane fractions containing approximately 10% of protein, approximately 30% of cholesterol in membranes of ventricular myocardium. Cholesterol-rich lighter membrane fractions contain >70% of Na, K-ATPase and caveolins 1 and 3 and <10% of beta-actin. Treatment of hypothyroid rats with T(3) increased the relative abundance of both alpha1 and beta1 Na, K-ATPase subunits in total membranes by 4- to 5-fold (with no change in caveolin-3), and resulted in 1.9-fold increase in enzyme activity. T(3)-induced Na, K-ATPase subunits were preferentially distributed to the lighter fractions (#s 4, 5 and 6); and increased abundance of alpha1 and beta1 were 34-70% and 43-68%, respectively. We conclude that the activity of Na, K-ATPase is not uniform in cardiac membranes, and while a significant amount of Na, K-ATPase is present in cardiac cholesterol-rich membrane fractions, the intrinsic activity is significantly less than the enzyme present in relatively cholesterol-poor membranes.