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.