Glucagon storage, release and degradation by tumoral islet cells (RINm5F line).

Tumoral islet cells of the RINm5F line contain and release glucagon. Over 90 min incubation, the secreted hormone represents about 50% of the final cell content (1.4 +/- 03 fg/cell). L-arginine augments modestly glucagon release, the relative magnitude of such an effect being inversely related to the concentration of D-glucose. The immunoreactive material secreted by the cells consists of both true glucagon (59-64%) and larger peptides. The RINm5F cells also release a proteolytic factor able to degrade exogenous glucagon or insulin. These results reveal that glucagon producing tumoral cells display several abnormal features in their secretory behaviour.