Serum levels of T4, T3, reverse T3, 3,3'-diiodothyronine and 3',5'-diiodothyronine in obesity, before and after jejuno-ileal bypass.

Serum T4, 3,5,3'triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3, rT3), 3,3'-diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2) and thyrotrophin (TSH) levels were studied in nineteen obese patients before and 6, 12, and 18, months after a jejuno-ileal bypass. Before surgery, the obese patients had increased serum T3 levels compared with a group of lean, matched controls (median: 1.94 nmol/l v. 1.44 nmol/l, P less than 0.01). Serum T3 decreased to normal (1.64 nmol/l) 18 months after surgery. A slight decrease was also observed in serum 3,3'-T2 levels, whereas progressive reductions in serum concentrations of rT3 and 3',5'T2 occurred. Eighteen months postoperatively the serum levels of rT3 and 3',5'-T2 had decreased from 0.676 nmol/l to 0.430 nmol/l (P less than 0.02) and 55.2 pmol/l to 40.0 pmol/l (P less than 0.01), respectively, and the values at 18 months were also reduced compared with the control group [0.722 nmol rT3/1 (P less than 0.01), 51.4 pmol 3',5'-T2/1 (P less than 0.01)]. concomitant with the decrease in serum level of the iodothyronines, serum TSH concentrations increased from 0 Micro U/ml to 0.9 microu/ml (P less than 0.01).