Circulating NSILA-s in Man: Preliminary Studies of Stimuliin Vivoand of Binding to Plasma Components

Abstract

The insulin-like peptide NSILA-s (nonsuppressible insulin-like activity soluble in acid ethanol) was measured in plasma using gel filtration in acid and a new radioreceptor assay. Total plasma NSILA-s levels, which are elevated in some patients with extrapancreatic tumors and hypoglycemia, were also found to be elevated in pregnancy. Patients with hypopituitarism had subnormal concentrations of total plasma NSILA-s which rose promptly and reached a peak 1 h after intravenous hGH. In contrast to this acute stimulus, chronic elevation of hGH resulted in an elevated level of NSILA-s in only 1 of 10 acromegalics. In normal subjects, oral gulcose loading resulted in a rise in NSILA-s (mean peak equals 151% of basal) while insulin induced hypoglycemia produced a small and variable fall. Among the other conditions studied, anorexia nervosa was associated with low levels of NSILA-s. Using gel filtration we found that at physiologic pH about 93% of endogenous NSILA-s is reversibly bound to larger molecules. We show that in normal adults the insulin-like bioactivity in plasma due to free NSILA-s in the basal state is equal to that exerted by insulin itself, and that the free NSILA-s in the circulation of patients with extrapancreatic tumors approximates the elevated level of insulin in patients with insulin-secreting pancreatic tumors.