Plasma cyclic nucleotide responses to insulin‐induced hypoglycaemia and methacholine in patients with hyperthyroidism

Abstract
The effect of insulin-induced hypoglycemia and methacholine on plasma c[cyclic]AMP and cGMP levels was studied in normal volunteers, hyperthyroid and hypothyroid patients. A significant positive correlation existed between the maximal increase in plasma cAMP and the maximal decrease in plasma glucose in normals during insulin-induced hypoglycemia. Therefore, the plasma cAMP response is considered to be dependent on the degree of hypoglycemia, rather than the insulin dose. The cAMP response to hypoglycemia was significantly higher in hyperthyroid patients, and was lower in patients with hypothyroidism than in normals. The cAMP response of the hyperthyroid patients was normalized when their hyperthyroidism was controlled after 3 mo. of treatment. The plasma cGMP level was slightly elevated during hypoglycemia, but there was no significant difference between controls and hyperthyroid patients. The cGMP response to methacholine, which is probably mediated by cholinergic receptors, was significantly potentiated in hyperthyroid patients. The cAMP response, which is presumably dependent on endogenous catecholamines secreted during methacholine-induced hypotension, was also enhanced in hyperthyroid patients. .beta.-Adrenergic receptor responses and cholinergic receptor responses [apparently] are both enhanced in hyperthyroidism.