Suppression of endogenous insulin secretion by exogenous insulin in patients with insulinoma.
OBJECTIVE
Previous studies have demonstrated that endogenous insulin secretion is not suppressed by exogenous insulin in patients with insulinoma. In this study we examined whether insulin secretion in insulinoma patients is suppressed by exogenous insulin during hypoglycaemia.


METHODS
Sixteen insulinoma patients (5 men and 11 women) and 10 normal subjects were studied. Hyperinsulinaemic glucose clamp studies were performed at both euglycaemia (4.5 mmol/l glucose) and hypoglycaemia (2.5 mmol/l glucose).


RESULTS
In normal subjects, plasma C-peptide levels were suppressed by 66% during the euglycaemic hyperinsulinaemic clamps (P < 0.01). In contrast, in insulinoma patients, plasma C-peptide levels increased by 25% during the clamps (P < 0.05). In the hypoglycaemic hyperinsulinaemic clamps, plasma C-peptide levels were nearly completely (91%) suppressed in normal subjects and partially (39%) suppressed in patients with insulinoma (P < 0.01). The decrease in C-peptide levels during the hypoglycaemic clamps was > 30% in 12 (75%) of 16 insulinoma patients and > 50% in 8 (50%) patients.


CONCLUSIONS
This study demonstrated that in patients with insulinoma, insulin secretion was not suppressed by exogenous insulin during euglycaemia but was suppressed during hypoglycaemia, although the degree of suppression was less than that in normal subjects. Our results suggest that the feedback regulation of insulin secretion by exogenous insulin is partially retained in patients with insulinoma.
Kim
C H
CH
Department of Internal Medicine, Asan Medical Centre, University of Ulsan College of Medicine, Seoul, Korea.
Park
J Y
JY
Shong
Y K
YK
Hong
S K
SK
Kim
G S
GS
Lee
K U
KU
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000378:metabolism; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000097:blood / Q000175:diagnosis*; D011237:Predictive Value of Tests
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin