Rapid changes in somatomedin activity during insulin-induced hypoglycemia: possible release of an inhibitory factor

Somatomedin activity was determined by bioassay during insulin-induced hypoglycemia in 24 patients with a variety of pituitary disorders. Initial somatomedin levels appeared to depend primarily on the state of GH secretion and were unaffected by abnormal PRL secretion. During the test, somatomedin activity fell to a minimum after 45 to 60 min and subsequently returned to initial values in those patients whose GH levels rose in response to insulin hypoglycemia, but not in patients lacking a GH response. Heat treatment of the plasma abolished the change in somatomedin activity in the majority of patients, and it is likely that the apparent fall in somatomedin was due to the presence of a heat-labile inhibitor of somatomedin action on cartilage.