The effects of an intravenous infusion of porcine GIP on β-cell secretion in patients
with untreated type 2 diabetes mellitus have been studied. The subjects were studied
on two separate days. After a 10 h overnight fast and a further 120 min basal period
they were given an intravenous infusion of porcine GIP (2 pmol · kg-1 · min-1) or control solution in random order from 120-140 min. Frequent plasma glucose, insulin,
C-peptide and GIP measurements were made throughout and the study was continued until
200 min. Plasma glucose levels were similar throughout both tests. During the GIP
infusion there was an early significant rise in insulin concentration from 0.058 ±
0.006 nmol/l to 0.106 ± 0.007 nmol/l (P < 0.01) within 6 min of commencing the GIP
infusion and insulin levels reached a peak of 0.131 ± 0.011 nmol/l at 10 min (P <
0.01). Insulin levels remained significantly elevated during the rest of the GIP infusion
(P < 0.01-0.001) and returned to basal values 20 min post infusion. No change in basal
insulin values was seen during the control infusion. C-peptide levels were similarly
raised during the GIP infusion and the increase was significant just 4 min after commencing
the GIP infusion (P < 0.05). GIP levels increased from 16 ± 3 pmol/l prior to the
infusion to a peak of 286 ± 24 pmol/l 20 min later. At 4 min when a significant β-cell
response was observed GIP levels were well within the physiological range. GIP is
insulinotropic in the fasting state in patients with untreated type 2 diabetes mellitus
and may stimulate the β-cell continuously throughout the day.
Glucose - Insulin - C-Peptide - Glucose Dependent Insulinotropic Polypeptide (GIP)
- Type 2 Diabetes Mellitus
