We investigated the major products of
proglucagon (PG) processing in plasma in the fasting state, after intravenous
arginine and after an oral
glucose load in noninsulin-dependent diabetics (
NIDDM) and in weight matched controls using specific radioimmunoassays and analytical gel filtration. In the fasting state the glucagonlike peptide-1 (GLP-1) immunoreactivity was significantly elevated in the
NIDDM group compared with the control group. Both after intravenous
arginine and after an oral
glucose load a rise in the plasma concentrations of all immunoreactive moieties measured was seen. All integrated incremental responses after intravenous
arginine were identical in the two groups. After oral
glucose the
insulin concentrations in plasma were lower and the concentrations of all
proglucagon products were higher in the
NIDDM group compared to the control group. The gel filtration analysis showed that
arginine stimulated the secretion of pancreatic
glucagon (PG 33-61), major
proglucagon fragment (PG 72-158) and probably
GLP-1 (PG 72-107
amide) in both groups, whereas oral
glucose stimulated the secretion of
glicentin (PG 1-69) and intestinal
GLP-1 (PG 78-107
amide), an insulinotropic
hormone. The elevated levels of immunoreactive
GLP-1 in diabetics in the fasting state were mainly due to an increased concentration of major
proglucagon fragment.