Impairment of Growth Hormone and Insulin Secretion in Hyperthyroidism

The pattern of growth hormone (GH) and im‐munoreactive insulin (IRI) secretion in response to insulin hypoglycaemia, arginine infusion and oral glucose load has been investigated in a group of hyperthyroid subjects. In twenty patients, compared with twenty normal controls, GH secretion was significantly reduced in response to both insulin hypoglycaemia and arginine infusion. Arginine‐induced IRI secretion was also clearly decreased. In ten patients who had undergone a 100 g oral glucose load, hyperglycaemia failed to suppress GH levels, which increased paradoxically. Slightly impoverished IRI secretion and impaired glucose tolerance were observed in these subjects. In five patients, re‐examined soon after restoration of euthyroidiszn, no significant changes in glucose tolerance and IRI secretion were noted; instead, a slightly improved GH response to the provocative stimuli and the restoration of a normal GH suppression by glucose were observed. – The possibility is emphasized that in hyperthyroidism an enhancement of the catecholamine effect induced by thyroid hormones is involved in the diminished GH and IRI secretion.