Plasma Insulin Studies in the Diagnosis of Insulinoma

Abstract

Plasma insulin levels were measured in 8 patients of whom 5 were surgically proven to have, and 3 had strongly suggestive evidence of, a functioning islet cell tumour. The fasting plasma insulin level was elevated in only 3 patients, despite repeated sampling. The administration of tolbutamide produced an excessive insulin response in 5 of the 8 patients, glucagon produced an excessive insulin response in 4 of 6 patients tested, 1-leucine produced a rise in plasma insulin in 1 of 2 subjects tested and the only subject studied after 50g. oral glucose had a high insulin response. The insulin response was highest after tolbutamide in all but one patient and this would appear to be the single most valuable test. However false negatives may occur and therefore the whole range of tests may have to be performed to establish the diagnosis. Two patients were studied during surgery and in one the insulin content of the tumour was assayed after extraction with acid alcohol. Four patients were studied again after treatment by surgery (2) and diazoxide (2) when normal insulin levels were found.

Hyperinsulin Response to Oral Leucine in Obesity and Acromegaly

“…In the present study there was no detectable insulin response to oral leucine in non-obese, normal, control subjects, even when double doses of L-leucine were administered. This imperceptible insulin response to oral leucine in normals has been reported by others (4)(5)(6)(7) and rnay relate to the lower plasma levels of leupine obtained with oral, compared to intravenous leucine administration (11).…”

“…However, when administered orally to humans, L-leucine is an ineffective (4)(5)(6)(7) or, at best, weak (8) stimulator of insulin release in normal subjects, yet a potent and often selective one in subjects with certain abnormal conditions. These include insulinoma (9), idiopathic familial hypogly-:emia (4), myotonic dystrophy (10), and normal subjects pretreated with chlorpropamide (8, 11).…”

Klinische, diagnostische und operationstechnische Erfahrungen mit B- Zelltumoren des Pankreas

“…Der Niichternspiegel des radioimmunologisch bestimmbaren Insulins (IRI) ist bei Patienten mit insulinproduzierendem Tumor gewShnlich erhSht [16,24,29].…”

“…Die F~higkeit der Zelle zur Synthese yon Insulin ist zwar erhalten, ihr Speicherungsverm6gen und die damit verbundene physiologisehe Sekretion aber gest6rt, d. h. die Zelle befindet sich im Zustand einer funktionellen Autonomie. Durch das Fehlen des Riickkoppelungsmechanismus ist die basale Insulinsekretion gesteigert, was dutch gleichzeitige Bestimmung der Seruminsulinkonzentration und der Blutglukosewerte im Niichternzustand und nach Stimulation deutlich gemacht werden kann [16,30].…”