Glucoregulation during and after intense exercise: effects of beta-blockade.
To define the roles of beta- and alpha-adrenergic receptors in intense exercise, 17 lean healthy fit young males underwent 13.6 +/- 0.2 (+/-SE) min of cycle ergometer exercise: 6 at 100% maximum oxygen uptake (VO2max; MAX), 7 at their maximum possible (87 +/- 2.3%) during iv propranolol (P; 150 micrograms/kg bolus 30 min preexercise, then 80 micrograms/kg.min), and 7 (including 3 of the P subjects) at 87% VO2max (C) as controls for P. Plasma glucose increased from similar resting values to a peak in the early recovery period at 7.2 +/- 0.44 in MAX and 6.8 +/- 0.37 in P, but only 5.2 +/- 0.3 mmol/L in C. The rate of glucose appearance (Ra) rose about 8-fold in both MAX and P, but only 4-fold in C (P = 0.001). The rate of glucose disappearance (Rd) increased 4-fold in MAX, 5.5-fold in P, and 3-fold in C (P = 0.001). Plasma insulin declined during exercise (P < 0.05) in MAX and P, but not in C, whereas plasma glucagon increased modestly in all groups. The mean peak plasma norepinephrine level was 36.3 +/- 4.5 in MAX, 20.2 +/- 3.4 in P, and 15.2 +/- 2.9 nmol/L in C (P = 0.002); epinephrine reached 7141 +/- 1790 in MAX and 5605 +/- 1532 in P (P = NS), but only 1715 +/- 344 pmol/L in C (P = 0.03). Therefore, 1) an "unmasked" alpha-adrenergic effect, directly and/or via an altered glucagon/insulin ratio, probably contributed to increased Ra with P treatment; and 2) the marked facilitation of the increase in Rd with P supports a major role for beta-adrenergic restraint of Rd at this exercise intensity.
Sigal
R J
RJ
McGill Nutrition and Food Science Center, Royal Victoria Hospital, Montreal, Quebec, Canada.
Purdon
C
C
Bilinski
D
D
Vranic
M
M
Halter
J B
JB
Marliss
E B
EB
D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D004837:Epinephrine / Q000097:blood; D016552:Ergometry; D015444:Exercise / Q000502:physiology*; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D011433:Propranolol / Q000097:blood
D000319:Adrenergic beta-Antagonists; D001786:Blood Glucose; D007328:Insulin; D005934:Glucagon; D011433:Propranolol; D005947:Glucose; D009638:Norepinephrine; D004837:Epinephrine