Thyroid function and plasma cyclic AMP response to intravenous glucagon.

The glucagon stimulated increase in plasma cyclic AMP has been studied in 17 healthy subjects, in 13 hyperthyroid and in 14 hypothyroid patients. Six hyperthyroid and 2 hypothyroid patients were re-investigated after at least 15 months of treatment. The results show: 1) The glucagon stimulated cyclic AMP response is significantly increased in hyperthyroid patients considered as a group, and is reduced in patients with hypothyroidism. 2) Three hyperthyroid and 4 hypothyroid patients showed a normal response to iv glucagon, indicating that the plasma cyclic AMP response to iv glucagon is not a sensitive test for the evaluation of peripheral thyroid states. This suggests that the effects of thyroid hormones in the liver does not necessarily follow the effects in other tissues. 3) Re-investigation of treated patients showed that the cyclic AMP response can be normalized by treatment, both in hyperthyroidism and hypothyroidism. However, in patients treated for hyperthyroidism a hyper-response to glucagon can continue after blood levels of thyroid hormones are reduced to normal. This suggests an inertia in the loss of the hyper-response to glucagon, once a hyperfunction has been induced. A similar inertia in the loss of glucagon sensitivity in hypothyroidism could explain the large number of normal tests in hypothyroid patients.