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 (VO(2)max; MAX), 7 at their maximum possible (87 +/- 2.3%) during iv propranolol (P; 150 mu g/kg bolus 30 min preexercise, then 80 mu g/kg . min), and 7 (including 3 of the P subjects) at 87% VO(2)max (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 (R(a)) rose about 8-fold in both MAX and P, but only 4-fold in C (P = 0.001). The rate of glucose disappearance (R(d)) 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 R(a) with P treatment; and 2) the marked facilitation of the increase in R(d) With P supports a major role for beta-adrenergic restraint of R(d) at this exercise intensity.