Changes in thyroid hormone levels during the treatment of ketotic diabetes

A case of hypersensitivity to thyroid hormones with normally functioning thyroid gland and increased nuclear triiodothyronine receptors

A 52-year-old male presented himself with tachycardia crises which appeared first during childhood, increased in frequency without goiter or exophthalmos. Cardiac and adrenergic diseases were excluded. The thyroid function was normal regarding T4, free T4 and T3, TBG, radioiodine uptake, TSH and T3 suppressibility; however the TSH response to TRH was decreased. The lymphocyte nuclear T3 receptor was found with an affinity close to that of normal volunteers (Ka: 1.42 x 10(10) M-1 vs 1.95 +/- 0.35 x 10(10) M-1) and a binding capacity markedly increased (9.9 vs 3.7 +/- 0.4 fmol T3/100 micrograms DNA). Pindolol was inefficient on the dysrhythmia which disappeared with carbimazole and relapsed after withdrawal of the antithyroid drug. Under carbimazole, the plasma T4 markedly decreased (27.7 +/- 3.6 nmol/l) but the patient remained euthyroid. The clinical course and the laboratory data suggest that the tachycardia crises are the consequence of a hypersensitivity of the heart to thyroid hormones, associated with an increased number of T3 nuclear receptor sites in lymphocytes.

Correlation between different degree and duration of metabolic control and thyroid hormone levels in type 1 and type 2 diabetics

Thyroxine (T4), triiodothyronine (T3), reverse T3 (rT3) and HbA1c were assayed in 21 insulin-dependent (type 1) diabetics and in 45 non-insulin-dependent (type 2) diabetics with normal thyroid function and different levels of control, and were compared to values found in apparently healthy controls. rT3 and rT3/T3 ratio were significantly increased both in type 1 and type 2 diabetics. T3 and T4 were significantly lower in type 2 diabetics than in the controls. Significant positive correlations of HbA1c to rT3 (r = 0.63) and to rT3/T3 ratio (r = 0.53) were found in type 1, and in type 2 diabetics (HbA1c, rT3-r = 0.50), (HbA1c, rT3/T3-r = 0.37). There was no correlation between glycemia (BG), relative body weight (RBW) and thyroid hormones. These data suggest that the alterations of thyroid hormones in type 1 and type 2 diabetes mellitus reflect the degree of control better than the hyperglycemia and the duration of metabolic unbalance.

Effect of diabetic control on the level of circulating thyroid hormones

Basal plasma levels of thyroxine (T4), triiodothyronine (T3) and reverse T3 were determined by radioimmunoassay in 44 control subjects, 44 Type 1 (insulin-dependent) and 39 Type 2 (non insulin-dependent) diabetic patients aged from 15 to 75 years. All were clinically euthyroid. The quality of diabetic control was assessed by the percentage of glycosylated haemoglobin. In both the diabetic groups there was a significant decrease in T3 and a rise in reverse T3 whereas T4 was normal. We found no significant differences between plasma thyroid hormone levels in Type 1 and Type 2 diabetic patients. In the poorly controlled diabetics (glycosylated haemoglobin greater than or equal to 12%), T3 was 90 +/- 5 ng/dl, which differed significantly from the level found in the better controlled patients (106 +/- 5 ng/dl, p less than 0.01). In the diabetic patients without associated illness, a negative linear correlation was found between T3 and glycosylated haemoglobin and a positive correlation between reverse T3/T3 and glycosylated haemoglobin. No correlation between T3 or reverse T3 and fasting blood glucose could be established. In conclusion, many diabetics showed a low T3 syndrome suggesting that there may be an impairment in the extrathyroidal conversion of T4 to T3. This may well be enhanced by a poor diabetic control (glycosylated haemoglobin greater than or equal to 12%).