Insulin levels in thyrotoxicosis and primary myxoedema: Response to intravenous glucose and glucagon

Glucose disappearance, insulin-like activity (ILA) and serum immunoreactive insulin (IRI) were studied after intravenous injection of glucose or glucagon in patients suffering from thyrotoxicosis or primary myxoedema. A group of normal subjects was also investigated. Glucose disappearance rate appeared to be normal in hyperthyroid, and markedly reduced in hypothyroid subjects. Fasting ILA levels were significantly higher than normal in myxoedema, and lower than normal in thyrotoxicosis. On the other hand, fasting IRI levels were higher than normal in myxoedema but normal in thyrotoxicosis. After glucose administration ILA in myxoedema remained at higher values than in thyrotoxicosis at any time of the study; in myxoedema, peak ILA levels were reached later than in thyrotoxicosis; peak IRI levels of similar magnitude were reached slightly earlier than normal in thyrotoxicosis, and later in myxoedema; in the latter condition, elevated IRI levels were observed for a longer period than in either euthyroidism or hyper-thyroidism. During this test the insulingogenic index showed only slight changes in normal and in thyrotoxic subjects, whereas it increased significantly up to 60 min in myxoedema. The data indicate that the reduced glucose utilization in hypothyroidism is not due to insulin deficiency, but rather to insulin resistance. It also seems possible that thyroid function influences the time of maximal insulin response to intravenous glucose administration. After glucagon injection, the increase in blood glucose was lower and shorter than normal in thyrotoxicosis; it was initially somewhat slower, but later higher and more sustained than normal, in myxoedema. The smaller increment in blood glucose in the former condition is probably connected with reduced glycogen stores. ILA response was very high and well sustained in myxoedema, whereas it was moderate and shortlasting in thyrotoxicosis. IRI response was higher than normal in hypothyroid subjects, and lower than normal in thyrotoxic subjects. No difference in the time required for maximal response was observed among the three groups.