Influence of hyper- and hypothyroidism on subcutaneous adipose tissue blood flow in man

Subcutaneous adipose tissue (AT) blood flow (BF) in the abdomen, thigh, and arm was determined by measuring the local clearance of [133]Xe in patients with untreated hyper- or hypothyroidism (n = 10, n = 7); six patients in each group were reexamined after treatment when they were euthyroid. Abdominal ATBF before treatment was 5.5 +/- 0.8 (SE) ml/min X 100 g AT in the hyperthyroid patients and 1.3 +/- 0.3 ml/min X 100 g AT in those who were hypothyroid. After therapy abdominal ATBF was 60% lower (P less than 0.05) in the hyperthyroid group and 80% higher (P less than 0.05) in the hypothyroid group. Similarly, ATBF in the thigh and arm was significantly reduced and increased, respectively, after treatment in the two groups. The blood glycerol level in the hyperthyroid group was 128 +/- 24 mumol/liter initially and was 50% lower (P less than 0.05) after therapy, whereas in the hypothyroid group blood glycerol levels were similar before (46 +/- 4 mumol/liter) and after therapy. Body fat, expressed as a percentage of body weight, was similar in the two groups before and after treatment. There was a positive correlation (P less than 0.001) between ATBF and serum T3 and T4 levels and an inverse correlation (P less than 0.01) between ATBF and plasma norepinephrine levels. Mean arterial blood pressure was similar in the two groups indicating that the alterations in ATBF were due to changes in vascular resistance. The results of this study suggest that thyroid hormones regulate sc ATBF in man.