T₄-T₃ Shift during the Postprandial Period After Glucose Load in Obese Children before and after Hypocaloric Diet - One Factor for Postprandial Thermogenesis?

Summary

Reactions of the plasma concentrations of the thermogenetically active thyroid hormones T₃ and T₄ were studied in overweight children during the postprandial period after glucose load before and after feeding a hypocaloric diet.

1. In a group of 14 overweight children, T₄ values decreased by 31 % (p < 0.001) 90 minutes after oral glucose load (1.75 g/kg). T₃ plasma concentrations did not fall - on the contrary a slight tendency to increase could be observed (8.7 % after 90 min). T₃/T₄-ratio increased to 50-60 % after 60 or 90 minutes respectively. In another group of 40 overweight children a fall of T₄ plasma concentration could also be seen after intravenous glucose load (0.33 g/kg) (with a minimum after 60 min, p < 0.001). It is postulated, that there is a glucose induced shift of T₄ to the particular thermogenetically active T₃ (increased T₄-T₃ conversion?) in obese children during the postprandial period which is characterized by an increased calorigenesis.

2. After feeding a diet of 600-1000 Kcal/die (30 % protein, 45 % carbohydrate, 25 % fat) over a period of 21 days, a fall of T₃ plasma concentrations could be estimated in 12 overweight children after glucose load (30 min p < 0.05 and 90 min p < 0.005, respectively). T₃/T₄ ratio was diminished to 69.4 % after 60 min compared with control values. In 6 out of 12 patients an increase of T₄ values associated with a fall of T₃ values was found after oral glucose load. An increase of T₄ values was also estimated in a group of 15 overweight children after 5-7 days fasting (p < 0.001). It is suggested that the constellation - elevated T₄ values and diminished T₃ values reflects a hypothyroid situation and hypocaloric diet and fasting leads to a reduced T₄-T₃ conversion in overweight children as well as in adults.

Key-Words:

Glucose - Triiodothyronine - Thyroxine - Children - Diet