IMPAIRED 3,5,3'-TRIIODOTHYRONINE (T3) PRODUCTION IN DIABETIC-PATIENTS

Serum concentrations of thyroxine (T4), 3,5,3′-triiodothyronine (T3), and 3,3′,5′-triiodothyronine (RT3) were measured in 50 patients with diabetes mellitus. The mean concentrations of serum T4, T3, and RT3 were 8.5 ± 3.7 (SD) μg/dl, 134 ± 41 ng/dl, and 30 ± 13 ng/dl, respectively, which were not significantly different from values of 33 normal control subjects. The serum T3 T4 ratio showed a significant inverse correlation with the level of fasting blood sugar (FBS) (p < 0.01). Turnover studies were carried out in seven normal control subjects and in 5 insulin-independent diabetic patients on T4 replacement. T4 turnover was similar in both groups. The T3 metabolic clearance rate of the diabetic patients was also normal (20.7 ± 4.0 liter/day/70 kg), but the T3 disposal rate was reduced when compared to that of normal control subjects (17.0 ± 5.6 vs. 40.6 ± 4.8 μg/day). The RT3 metabolic clearance rate (80.6 ± 20.2 vs. 105.0 ± 14.0 liter/day/70 kg) and the RT3 disposal rate (29.4 ± 10.8 vs. 49.4 ± 11.6 μg/day) were both reduced in the diabetic patients. In five other diabetic patients on 3 wk of oral T4 replacement, the serum T3 T4 ratio was below the normal range (0.0059 ± 0.0041 vs. 0.0152 ± 0.0011) and remained unchanged during insulin infusion during 10 hr. The T3 T4 ratio increased but remained below the normal range after 10 days of dietary and insulin treatment (0.0083 ± 0.0032; p < 0.05). Our results suggest that T3 production from peripheral T4 monodeiodination is impaired in uncontrolled diabetic patients. This impairment in T3 production is correlated with the impairment of glucose utilization. © 1979.