Igf-i inhibits the burst mass of pulsatile insulin secretion at
supraphysiologic and low igf-i infusion rates.
P[stod]orksen, Niels, Mehboob A. Hussain, T. L. Bianda, Birgit Nyholm,
Jens S. Christiansen, Peter C. Butler, Johannes D. Veldhuis.
E. Rudi Froesch, Ole Schmitz
APStracts 3:0232E, 1996.
Insulin-like growth factor-I (IGF-I) shares structural and functional
features with insulin, affects carbohydrate metabolism and inhibits
insulin secretion. Insulin secretion is pulsatile, and is regulated
by changing frequency and/or mass of secretory bursts. To examine the
mechanism of IGF-I's inhibition of insulin secretion, 8 healthy
volunteers were studied 3 times. During glucose infusion (2.5
mg/kg/min) blood was sampled minutely times 75-200 minutes for
triplicate insulin concentration measurements by ELISA (CV 2.1 %).
Time 125 min infusion of saline, low-dose IGF-I (0.025 [mu]g/kg/min)
or high-dose IGF-I (0.15 [mu]g/kg/min) was commenced and continued
until 200 min. Data were compared before (75-125 min) versus during
infusion (150-200 min). Insulin concentration time series were
deconvolved, using validated pulse-detection criteria, to assess
insulin secretory burst mass and frequency. During saline infusion no
time effect occurred. Following IGF-I infusion, serum C-peptide
decreased (582 +/-85 pM vs 481 +/-82 pM, low-dose IGF-I,
p<0.05; 539 +/-84 vs 427+/-69, high-dose IGF-I,
p<0.01). Total insulin secretion rates decreased by 17 % and
21 % respectively, via specific inhibition of the insulin secretory
burst mass (31 +/-8 vs 20 +/-4 pmol/mL, low-dose IGF-I, p=0.06; 22
+/-4 vs 17 +/-3 pmol/mL, high-dose IGF-I, p<0.05), whereas the
frequency was not affected (10.5 +/-1.3 vs 10.7 +/-1.3 pulses/hour,
low-dose IGF-I, p=0.85; 8.7 +/-1.0 vs 11.1 +/-1.2 min/pulse, high
-dose IGF-I, p=0.15). We conclude that IGF-I inhibits pulsatile
insulin secretion by specific inhibition of mass but not frequecy of
secretory bursts.
Received 10 June 1996; accepted in final form 31 October 1996.
APS Manuscript Number E282-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996