Altered pulsatile insulin secretion associated with endurance training. Engdahl, Jill, Johannes D. Veldhuis, and Peter A. Farrell. Noll Physiological Research Center and Department of Exercise and Sport Science, The Pennsylvania State University, University Park, Pa. 16802 and Division of Endocrinology and Metabolism, University of Virginia Health Sciences Center and National Science Foundation Center for Biological Timing, Charlottesville, Va. 22908
APStracts 2:0322A, 1995.
Endurance exercise training reduces glucose-stimulated insulin secretion while elevating insulin action on target tissues. Under some conditions, hormone action is enhanced by pulsatile delivery to tissues. We tested the hypothesis that different insulin secretory pulse profiles would be observed in endurance trained vs sedentary men. Seven endurance trained (T, VO2max = 62.5 +/- 4.3 ml.kg-1.min -1), mean+/-sd, and 7 untrained (UT, 40.3 +/- 3.3 ml.kg-1.min-1 ) age- and weight-matched men were studied. All subjects had normal oral glucose tolerance test however the insulin responses for T were significantly lower (p&LT0.05) than UT. After two days of no exercise and an overnight fast, arterialized venous blood was sampled at 1 min intervals for 120 min and assayed for insulin. Characteristics of the insulin pulse profile were quantified using deconvolution analysis. The mass of insulin secreted per burst was significantly lower for T= 50.1 +/- 14 vs UT= 107.4 +/- 35 pM.min-1, (p&LT0.05), mean+/-se, as was the peak height per burst (T=14.3+/- 5, UT=37.5 +/- 3.2 pM), rate of insulin production (T=429.6 +/- 161 vs UT=1002.4 +/- 393 pmol. 90 min-1) and mean plasma insulin concentration (T= 32.2 +/- 17 vs UT=53.7 +/- 35 pM). The interpulse interval between bursts and the half-duration of insulin secretory bursts were not significantly different between groups. Nonpulsatile basal insulin secretion was similar for T= 3.58+/-1.6 and UT=5.55+/ -2.3 pM.min-1. These data show that regular endurance exercise in young men is associated with an insulin pulse profile in the resting fasted state characterized by less insulin secreted per burst, but a similar number of bursts over a 90-min period. As a working hypothesis, we suggest that training-induced elevations in target -tissue sensitivity to insulin reduce the requirement for pulsatile insulin secretion. 

Received 27 March 1995; accepted in final form 12 July 1995.
APS Manuscript Number A337-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.