It is over 40 years since the original demonstration that thyroxine (T4), the principal secretory product of the thyroid, is deiodinated, to 3,5,3'-tri-iodothyronine (T3) in peripheral mammalian tissues. Subsequently it was shown that the antithyroid drug propylthiouracil (PTU) also blocked the metabolic effects of administered T4 in proportion to its inhibition of T4 to T3 conversion, indicati...

While 3, 3', 5'-triiodothyronine (reverse T3, rT3) has been detected both in human serum and in thyroglobulin, no quantitative assessment of its metabolic clearance rate (MCR), production rate (PR), or secretion by the thyroid is yet available. This study examines this information in euthyroid subjects and evaluates it in light of similar information about two other iodothyronines in the thyroi...

Although thyroxine (T4) 5'-deiodinase activity is diminished in liver homogenates of starved rats, no information is available regarding the effect of starvation on net T4 to triiodothyronine (T3) conversion in the intact rat. It appeared important to clarify this relationship since rat liver homogenates are widely used as a model for the study of the factors responsible for reduced circulating...

Studies of the rate of extrathyroidal conversion of thyroxine (T4) to 3,5,3'-triiodo-L-thyronine (T3) were carried out in rats. Total body homogenates were prepared and extracted with ethanol 48, 72, and 96 hr after the intravenous injection of (125)I-T4. (131)I-T3 was added, and the paper chromatographic purification of T3 was effected by serial elution and rechromatography in three paper and ...

TSH secretion is decreased by both T4 and T3. This negative feedback control ofTSH secretion has been correlated with an increase in pituitary nuclear T3 content, and it is not clear whether T4 exerts its effect directly on the thyrotroph or after its deiodination to T3. However, levels of the pituitary enzyme catalyzing T4 to T3 conversion, 51)-II, are decreased in the presence of an increased...

Numerous studies have suggested a marked correlation between thyroid functionality indices and lipid metabolism. In this trial we assessed the functional parameters of 165 individuals over 70, 87 women and 78 men, correlating the serum values of T3, T4, FT4, TSH with cholesterol, triglycerides, HDL, Apo-A and Apo-B levels. The correlation was performed over the whole population studied and subs...

It is known that some nutrients can have both negative and positive effects on some populations of insects. To test this, the Logrank test and the Interval Overlap Test were evaluated for two crop cycles (February-May and May-August) of the 7705 tomato hybrid, and the effect on the psyllid, Bactericera cockerelli (Sulc.) (Hemiptera: Triozidae), was examined under greenhouse conditions. Tomato p...

The comparative effects of equimolar doses of thyroxine (T4) and tri-iodothyronine (T3) were studied on fattening, gonadal status and moulting in thyroidectomized female spotted munia. The effects of suppression of peripheral conversion of T4 to T3 were also studied on these parameters. T4 administration led within 10 days to a significant regression of gonads and mobilization of fat, the respo...

The plasma triiodothyronine (T3) and thyroxine (T4) ratios have been evaluated in kwashiorkor and diet-induced obese weaned rats. The concentrations of T3 and T4 were determined in plasma by radio-immunoassay. A significant decrease in T3 level in the order kwashiorkor < obese < control was observed. However T4 concentration was more elevated (P < 0.01) in the obese than the normal controls, wh...