Inhibition of nuclear binding of triiodothyronine by antimycin A in cultured human fibroblasts.

We have tested the effects of several cell inhibitors on cell and nuclear content of T3 at equilibrium in cultured human fibroblasts. Monodansylcadaverine and colchicine inhibited in parallel, and near to the same extent, cell and nuclear content of T3. Antimycin A did not interfere with cell accumulation of T3 but induced a 10-fold decrease of nuclear T3. This effect was due to a decrease of the apparent affinity constant of the T3 nuclear receptor. Other metabolic inhibitors such as sodium azide or potassium cyanide were without effects. It is suggested that antimycin A blocks a nuclear T3 concentrating mechanism which maintains a gradient of free T3 between the nucleus on the one hand, and the cytosol and plasma, on the other.

Plasma glucose, insulin, proinsulin, C-peptide and glucagon before and after a carbohydrate-rich meal in hyperthyroid patients.

The function of the pancreatic B- and A- cell during a carbohydrate-rich meal was investigated in hyperthyroid patients, since these patients frequently present an altered handling of glucose. In basal conditions the plasma levels of glucose, immunoreactive insulin (IRI), C-peptide (CPR), proinsulin were higher in hyperthyroid patients than in normal subjects, whereas plasma glucagon was similar in the two groups. Hyperthyroid patients had high post-breakfast incremental areas of glucose and IRI and those of CPR and glucagon were normal. In post-breakfast plasma, the hyperthyroid patients had high proinsulin and normal insulin levels. The molar ratio between CPR and IRI was low throughout the test in the hyperthyroid group. In conclusion, in the hyperthyroid group the plasma levels of proinsulin were high and those of glucagon were normal; in response to the standard breakfast the levels of insulin and C-peptide were normal. These findings do not explain the altered glucose handling present in these patients.