Apparent Insulin Activity in a Fibrosarcoma Associated With Spontaneous Hypoglycemia*

Using the glucose uptake of the isolated rat hemidiaphragm or the rat cpididymal fat pad as an assay procedure, a glucose-uptake stimulator was extracted and concentrated from a large retroperitoncal fibrosarcoma removed from a patient with spontaneous hypoglycemia. Fractionation revealed the coexistence of an in vitro glucose-uptake inhibitor in the tumor. The glucoseuptake stimulating activity in a 22 per cent ethanol precipitate was destroyed by heating, but it was relatively heat-stable when in the form of the more concentrated zinc acetate precipitate. The stimulating activity was nondialyzable. The material which inhibited glucose uptake appeared to be heat-stable and dialyzable.