Thyroxine an triiodothyronine kinetics and extrathyroidal peripheral conversion rate of thyroxine to triiodothyronine in healthy elderly humans.

The influence of age on the kinetics of thyroxine (T4) and triiodothyronine (T3), and on peripheral conversion of T4 to T3, has been studied, comparing a group of euthyroid, healthy, elderly individuals to a group of young individuals. A monocompartment model was adopted for the kinetics of T4, while a bicompartment model was used for T3. No significant difference (p greater than 0.05) could be found in any of the kinetic parameters of T4 between the elderly and young groups. However, the following significant (p less than 0.05) changes were noted for T3: an increased disposition constant in the phase of slow distribution (beta), shortening of the half-life of this phase (T 1/2 beta ), elevation of the central distribution volume Vc and the elimination constant K23, reduction of the K12: K23 ratio, and increased plasma metabolic clearance and hormonal daily turnover. No significant differences (p greater than 0.05) were observed for the percent turnover of T4 converted to T3.

The kinetics of the thyroid hormones and the peripheral conversion rate of thyroxine to triiodothyronine in acute liver insufficiency under experimental conditions.

The kinetics of triiodothyronine (T3) and thyroxine (T4) were studied in 20 ewes. Ten were used as the control group, the other 10 received massive hepatic lesions induced by the ingestion of carbon tetrachloride. Half of each group were i.v. injected with 125IT3 or 125IT4, following a plasma disappearance over 96 hours. The amount of hormone present in each plasma sample was determined by immunoextraction procedure. The data was adjusted to the open two-compartment model. The hepatic insufficiency provoked a decrease in the disposition consent of T3, an increase in th plasma half-life of the distribution phase as well as a moderately decreased turnover rate of this hormone. The T4 kinetics were altered during acute hepatic insufficiency in the decrease of the elimination constant K13 and hormone plasma turnover rate. The study of the peripheral conversion rate based on the kinetic data showed an extrathyroidal conversion of T4 to T3 in the control sheep, none being detected in the sheep with induced hepatic insufficiency.

Study of the kinetics of the thyroid hormones and the peripheral conversion rate of thyroxine to triiodothyronine in acute renal insufficiency under experimental conditions.

We studied the kinetic behavior of triiodothyronine (T3) and thyroxine (T4) in two groups of 10 sheep. One was used as the control group (I) and the other consisted of sheep with acute renal failure (A.R.F.) induced by an iv. injection of mercuric dichloride. Five sheep of each group were injected with 125IT3 and the remaining five with 125IT4, later taking periodical extractions throughout the first 96 hours. The radioactive contaminants in the plasma were eliminated by extracting the hormones through immunoextraction. The mathematical calculation of the kinetics was based on the open two-compartment model. The A.R.F. caused a decrease in the disposition constant of the slow phase in the T3 kinetics, while at the same time prolonging the plasma half-life of the phase. The steady state distribution volume increases and the distribution constant K21 decreases in the group suffering from renal insufficiency. As regards the T4, all the kinetic parameters were altered with the exception of the distribution volumes, the most significant changes being the shortening of the plasma half-life in the end phases, the rise of the elimination constant K13 and the increase in the plasma clearance and thyroxine turnover rates. The analysis of the peripheral conversion rate revealed with a great amount of variation, that there is evidence of the conversion of T4 to T3 in the healthy group while this phenomenon remains undetected in the sick animals.

[New enzymatic and endocrinological aspects in two cases of Werner's syndrome (author's transl)]. / Nuevos aspectos enzimáticos y endocrinológicos en dos casos de síndrome de Werner.

Results of endocrinological studies and of the investigation of intraerythrocytic glycolytic pathway carried out in two patients with Werner's syndrome are presented. An increase of glyceraldehyde 3-phosphate and 3-phospho-glycerokinase has been observed, but the significance of these original findings is still unknown. An hyperinsulinism after oral glucose overload has been demonstrated too. This finding, which has been reported by other authors, probably reflects a peripheral resistance to insulin action. Other endocrinological abnormalities were a decrease in the T3:T4 quotient and a slight delay in the FSH-LH peak to LH-RH.