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Abstract
The binding of labelled 3,3′-di-iodo-l-thyronine (3,3′-T2) to isolated rat liver mitochondria has been characterized. Specific binding could be detected only in the inner mitochondrial membrane, not in other mitochondrial subfractions. The composition of the incubation medium influenced the binding capacity, the best combination of high specific binding and low non-specific binding being observed in phosphate buffer, pH 6·4.
The specific binding of 3,3′-T2 to mitochondria requires low ionic strength: concentrations of K+ and Na+ higher than 10 mmol/l and 0·1 mmol/l respectively resulted in a decreased binding capacity. The optimal calcium ion concentration was in the range 0·01–1·0 mmol/l. Varying magnesium ion, over the range of concentrations used (0·1–100 mmol/l), had no effect. Both ADP and ATP, at over 1 mmol/l, resulted in an inhibition of the specific binding. Incubation with protease resulted in a decrease in specific binding and an increase in non-specific binding, thus indicating the proteic nature of the binding sites. In addition to the above factors in the local environment the thyroid state of the animal might influence the 3,3′-T2-binding capacity. In fact, the thyroid state of the animal seemed not to have an influence on the affinity constant, but it did affect binding capacity.
Journal of Endocrinology (1997) 154, 119–124
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At present, there is growing evidence implicating GH and/or IGF-I in the intricate cascade of events connected with the regulation of heart development and hypertrophy. Moreover, GH excess and/or deficiency have been shown to include in their advanced clinical manifestations almost always an impaired cardiac function, which may reduce life expectancy. This finding is related both to a primitive impairment of heart structure and function and to metabolic changes such as hyperlipidemia, increase of body fat and premature atherosclerosis. Patients with childhood or adulthood-onset GH deficiency have a reduced left ventricular mass and ejection fraction and the indexes of left ventricular systolic function remain markedly depressed during exercise. Conversely, in acromegaly the cardiac enlargement, which is disproportionate to the increase in size of other internal body organs, has been a rather uniform finding. The severity of the acromegalic cardiomyopathy was reported to be correlated better with the disease duration than with circulating GH and/or IGF-I levels. Myocardial hypertrophy with interstitial fibrosis, lymphomononuclear infiltration and areas of monocyte necrosis often results in concentric hypertrophy of both ventricles. The treatment of GH deficiency and excess improved cardiac function. Interestingly, based on the evidence that GH increases cardiac mass, recombinant GH was administered to patients with idiopathic dilated cardiomyopathy. It increased the myocardial mass and reduced the size of the left ventricular chamber, resulting in improvement of hemodynamics, myocardial energy metabolism and clinical status. These promising results open new perspectives for the use of GH in heart failure.
Journal of Endocrinology (1997) 155, S33–S37