Abstract des Autors

To examine the role of beta-adrenergic mechanisms in the regulation of endogenous glucose (Glu) production (rate of appearance (Ra)) and utilization (rate of disappearance (Rd)) and carbohydrate (CHO) metabolism, six horses completed consecutive 30-min bouts of exercise at ca. 30% (Lo) and ca. 60% (Hi) of estimated maximum O2 uptake with (P) and without (C) prior administration of the beta-blocker propranolol (0.22 mg/kg iv). All horses completed exercise in C; exercise duration in P was 49.9+/-1.2(SE) min. Plasma Glu was unchanged in C during Lo but increased progressively in Hi. In P, plasma Glu rose steadily during Lo and Hi and was higher (P<0.05) than in C throughout exercise. Plasma insulin declined during exercise in P but not in C; beta-blockade attenuated (P<0.05) the rise in plasma glucagon and free fatty acids and exaggerated the increases in epinephrine and norepinephrine. Glu Ra was 8.1+/-0.8 and 8.4+/-1.0 micro-mol/kg/min at rest and 30.5+/-3.6 and 42.8+/-4.1 micro-mol/kg/min at the end of Lo in C and P, respectively. During Hi, Glu Ra increased to 54.4+/-4.4 and 73.8+/-4.7 micro-mol/kg/min in C and P, respectively. Similarly, Glu Rd was ca. 40% higher in P than in C during Lo (27.3+/-2.0 and 39.5+/-3.3 micro-mol/kg/min in C and P, respectively) and Hi (37.4+/-2.6 and 61.5+/-5.3 micro-mol/kg/min in C and P, respectively). Beta-blockade augmented CHO oxidation (CHOox) with a concomitant reduction in fat oxidation. Inasmuch as estimated muscle glycogen utilization was similar between trials, the increase in CHOox in P was due to increased use of plasma Glu. We conclude that beta-blockade increases Glu Ra and Rd and CHOox in horses during exercise. The increase in Glu Rd under beta-blockade suggests that beta-adrenergic mechanisms restrain Glu Rd during exercise. Verf.-Referat