Multicompartmental analysis of triiodothyronine (T3) distribution and metabolism in clinically euthyroid obese...

Triiodothyronine (T3) kinetic studies were performed on ten clinically non-fasting euthyroid obese individuals and on eight normal subjects. Kinetic analysis was carried out according to a three-pool model whose basic approach involved the acquisition of data from both vascular and extravascular sources. The former were represented by the plasma disappearance curves of iv injected radiolabeled T3. The latter included fecal and urinary losses and liver, kidney and thigh uptake. A detailed comparison of the T3 kinetics of obese and normal individuals did not uncover many differences between these two groups in the way the hormone is distributed, metabolized and excreted. The mean value for the plasma equivalent distribution volume of T3(VD3) in obese individuals (27.05 L) was not significantly different from that in controls (24.60 L) nor were significant differences observed between the mean value for the plasma appearance rate of the hormone (PAR3) in obese subjects (29.80 micrograms/day) and that in controls (30.05 micrograms/day). The mean value for the size of the slow pool (Qc), including fatty tissue as well as skeletal muscle, was unchanged in obese individuals when compared with controls, although in the obese subjects the mean value for the mass of fatty tissue was about 5 times greater. In addition, in obese individuals, the mean value for the fractional rate transfer from plasma to the slow pool (Kca), which was 9.06 day-1, did not significantly differ from that in controls (9.22 day-1).(ABSTRACT TRUNCATED AT 250 WORDS)