Insulin Secretion and Glucose Kinetics During Exercise With and Without Pharmacological α1- and α2-Receptor Blockade
- 1Department of Medical Physiology, the Panum Institute, University of Copenhagen, Copenhagen
- 2Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen
- 3Department of Anesthesia, Rigshospitalet, Copenhagen
- 4Department of Clinical Physiology and Nuclear Medicine, Herlev Hospital, Herlev, Denmark
Abstract
The mechanism behind exercise-induced decreases in plasma insulin concentrations was examined in eight healthy young men. In addition, the influence of specific α1- and α2-adrenoceptor blockade on glucose kinetics during exercise was studied. To test the hypothesis that exercise-induced decreases in insulin secretion are mediated via α2-adrenoceptors, all subjects exercised for 60 min on separate occasions under four conditions: with and without α1-receptor blockade (1 mg prazosin) and with and without or α2-receptor blockade (15 mg yohimbine). Glucose kinetics were measured using [3-3H]glucose. During exercise with α2-receptor blockade, the insulin concentration initially increased (first 20 min) then decreased, whereas it continually decreased in the corresponding control experiment. The C-peptide concentration did not change during exercise with α2-receptor blockade but decreased in the control experiment. During exercise with α1-receptor blockade and corresponding control experiments, insulin and C-peptide levels always decreased. With α1-receptor blockade, the glucose concentration increased (first 30 min) and then decreased, whereas it slightly decreased in all other experiments. In addition, with α1-receptor blockade, the glucose rate of appearance (Ra) increased rapidly (because of higher catecholamine concentrations in α1-receptor blockade versus control) and the glucose rate of disappearance (Rd) was higher compared with control. During exercise with α2-receptor blockade, the Ra and Rd were always lower compared with control. Therefore, we conclude that exercise-induced decreases in insulin secretion are mediated via α2-adrenoceptors and that blockade of α1- and α2-adrenoceptors during exercise elicits opposite responses in glucose Ra and Rd.
Footnotes
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Address correspondence and reprint requests to Flemming Dela, MD, Associate Professor, Department of Medical Physiology, the Panum Institute, Bldg. 12.4.7., University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark. E-mail: f.dela{at}mfi.ku.dk.
Received for publication 14 November 2000 and accepted in revised form 24 April 2001.
ANOVA, analysis of variance; FFA, free fatty acid; MCR, metabolic clearance rate; Ra, rate of glucose appearance; Rd, rate of glucose disappearance.
