MEASUREMENT OF SMALL QUANTITIES OF INSULIN-LIKE ACTIVITY WITH RAT ADIPOSE TISSUE. IV. SERUM INSULIN-LIKE ACTIVITY AND TUMOR INSULIN CONTENT IN PATIENTS WITH FUNCTIONING ISLET-CELL TUMORS*

Abstract

Serum insulin-like activity (ILA) in epididymal rat adipose tissue was measured in 23 patients with histologically confirmed islet-cell tumors. The mean serum ILA of these patients was significantly greater than that of 118 control subjects, and the values obtained in 9 patients exceeded the full normal range. Postoperative values were obtained in 10 patients without recognizable recurrence or metastases. All of these postoperative values were within the normal range, and in 8 instances, the individual decrease observed was significant; it was not significant in the other two patients. These data agree with previous reports employing either the rat hemidiaphragm bioassay for insulin activity or the immunoassay procedure. Measure ments of serum insulin or ILA are diagnostic in approximately one-third of the patients with islet-cell tumors. Patients with islet-cell tumors showed no significant change in serum ILA after rapid intravenous glucose loading, whereas normal subjects exhibited a threefold increase in serum ILA 20 minutes after the infusion of glucose. The insulin content of 10 islet-cell tumors was determined, and varied from 0.8 to 60 U per g wet weight. There was no apparent relationship between tumor insulin concentration and preoperative serum ILA. Islet-cell tumors with functioning metastases had lower tumor insulin concentration than tumors without metastases. For comparison and for control of the acid ethanol and the resin extraction techniques used in these studies, insulin content of pancreases obtained at autopsy was determined in 10 nondiabetic and 13 diabetic subjects. The values obtained showed close agreement between the two techniques, as well as with published data.