Distribution of plasma glucagon immunoreactivity in a patient with suspected glucagonoma

Gel filtration of plasma from a patient with a clinical syndrome of glucagonoma and a total plasma glucagon level of 2600 pg/ml, revealed the four glucagon immunoreactive fractions found in normal subjects. The total hyperglucagonemia observed was due to high levels of true glucagon and proglucagon moieties. The so-called "big plasma glucagon" (BPG) measured 190 pg/ml (normal average 113 +/- 79 pg/ml, Mean +/- SD, N = 10); the large glucagon immunoreactivity, LGI (9000 mol wt), measured 625 pg/ml (normal average 11 +/- 16 pg/ml); the true glucagon accounted for 1435 pg/ml (normal average 31 +/- 29 pg/ml); and the small glucagon immunoreactive fraction (approximately 2000 mol wt) measured 35 pg/ml (normal average 26 +/- 18 pg/ml). The high levels of LGI, considered a candidate for proglucagon, may reflect the increased secretory activity of the tumor.