Investigation of the usefulness of the plasma adenosine 3' 5' - cyclic monophosphate response to glucagon in thyroid disease.

The plasma adenosine 3', 5' - cyclic monophosphate (cyclic AMP) response to 50 micrograms of intravenous glucagon was examined in 14 normal euthyroid subjects, 15 patients with thyrotoxicosis and 5 patients with myxedema. The cyclic AMP responses to 50 micrograms of intravenous glucagon was significantly higher in the hyperthyroid group than in the euthyroid or hypothyroid group. However, the areas of overlap between all three groups were large and there was little relationship between the plasma cyclic AMP response to glucagon and the biochemical assessment of thyroid function. Serial studies of the response to 50 micrograms glucagon were carried out in four patients receiving treatment for thyrotoxicosis. Again, there was not consistent relationship between the plasma cyclic AMP responsiveness to glucagon and the free thyroxine index. It is concluded that although the plasma cyclic AMP response to glucagon is increased in thyrotoxicosis and decreased in myxedema, the variability of this response in thyroid disease precludes its use as a tissue index of thyroid hormone responsiveness.