A novel hyperglycaemic clamp for characterization of islet function in humans: assessment of three different secretagogues, maximal insulin response and reproducibility.
BACKGROUND
Characterization of beta-cell function in humans is essential for identifying genetic defects involved in abnormal insulin secretion and the pathogenesis of type 2 diabetes.


METHODS
We designed a novel test assessing plasma insulin and C-peptide in response to 3 different secretagogues. Seven lean, healthy volunteers twice underwent a 200 min hyperglycaemic clamp (10 mmol L-1) with administration of GLP-1 (1.5 pmol. kg-1. min-1) starting at 120 min and an arginine bolus at 180 min. We determined glucose-induced first and second-phase insulin secretion, GLP-1-stimulated insulin secretion, arginine-stimulated insulin response (increase above prestimulus, DeltaIarg) and the maximal, i. e. highest absolute, insulin concentration (Imax). Insulin sensitivity was assessed during second-phase hyperglycaemia. On a third occasion 6 subjects additionally received an arginine bolus at > 25 mM blood glucose, a test hitherto claimed to provoke maximal insulin secretion.


RESULTS
Insulin levels increased from 46 +/- 11 pM to 566 +/- 202 pM at 120 min, to 5104 +/- 1179 pM at 180 min and to maximally 8361 +/- 1368 pM after arginine (all P < 0.001). The within subject coefficients of variation of the different secretion parameters ranged from 10 +/- 3% to 16 +/- 6%. Except for second-phase which failed to correlate significantly with DeltaIarg (r = 0.52, P = 0.23) and Imax (r = 0.75, P = 0.053) all phases of insulin secretion correlated with one another. The insulin concentration after the arginine bolus at > 25 mM glucose (n = 6) was 2773 +/- 855 pM vs. 7562 +/- 1168 pM for Imax (P = 0.003).


CONCLUSIONS
This novel insulin secretion test elicits a distinct pattern of plasma insulin concentrations in response to the secretagogues glucose, GLP-1 and arginine and is highly reproducible and can be used for differential characterization of islet function.
Fritsche
A
A
Eberhard-Karls-Universität, Tübingen, Germany.
Stefan
N
N
Hardt
E
E
Schützenauer
S
S
Häring
H
H
Stumvoll
M
M
D000328:Adult; D001120:Arginine / Q000008:administration & dosage / Q000009:adverse effects; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis / Q000378:metabolism*; D005260:Female; D005934:Glucagon / Q000008:administration & dosage / Q000009:adverse effects / Q000097:blood / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D005947:Glucose / Q000008:administration & dosage; D015309:Glucose Clamp Technique / Q000009:adverse effects / Q000592:standards*; D006801:Humans; D006943:Hyperglycemia / Q000175:diagnosis / Q000378:metabolism*; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007333:Insulin Resistance; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism / Q000502:physiology*; D008297:Male; D010446:Peptide Fragments / Q000008:administration & dosage / Q000009:adverse effects / Q000378:metabolism; D011498:Protein Precursors / Q000008:administration & dosage / Q000009:adverse effects; D015203:Reproducibility of Results
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; C055453:glucagon-like peptide 1 (7-36)amide; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D001120:Arginine; D005947:Glucose