Studies of immunoreactive insulin (IRI) and human growth hormone (HGH) secretion were undertaken in a subject with chronic hypoglycemia associated with hepatoma. Fasting IRI concentrations were below 3 μU./ml. at glucose concentrations of 30 mg./100 ml. IRI secretion was not stimulated by acutely administered glucose, tolbutamide, glucagon or arginine. IRI concentrations rose after tolbutamide when plasma glucose was raised to 100 mg./100 ml. by sustained glucose infusion. Fasting ILA (muscle, adipose) levels were not elevated.
Fasting HGH concentrations were below 5 mμg./ml.; secretion was stimulated by arginine despite hypoglycemia. During glucose administration, HGH concentrations rose to 45 mμg./ml. as FFA levels fell from 2,250 to 233 μEq./L. Estimated total glucose utilization rate was high (7.5 mg./kg./hr. at a plasma glucose concentration of 100 mg./100 ml.).
(1) Glucose, or some metabolic product is required for human insulin secretion; (2) HGH secretion after arginine is not inhibited at low glucose concentrations; (3) FFA may exert an inhibitory role in HGH regulation; (4) Hypoglycemia in our subject with hepatoma was associated with increased glucose utilization, not with hyper-insulinism.
