Glucoregulation during and after intense exercise: effects of beta-blockade.

Abstract

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.

Characterization of circannual patterns of metabolic recovery from activity inRana catesbeianaat 15°C

“…Frogs on the other hand, appear to follow a more 'mammalian' pattern, of significant increases in blood glucose in response to activity (Fig.·4B), coinciding with and presumably due to catecholamine release (Fournier et al, 1994). Mammals restore normoglycemia within 1·h of epinephrine clearance (Sigal et al, 1994), whereas significant hyperglycemia was persistent over the 4·h of recovery in this study (Fig.·3C) and that of Fournier et al (Fournier et al, 1994).…”

Intense Exercise Has Unique Effects on Both Insulin Release and Its Roles in Glucoregulation

“…On the basis of these three studies, we have suggested that during intense exercise both ␣-and ␤-receptor effects of catecholamines can increase GP (35,36,40). Because with blockade of either of the receptors the plasma concentrations of catecholamines rose considerably more, this suggests that one system can compensate for the attenuated activity of the other, i.e., there is redundancy in the receptor mechanisms in this specific situation.…”

“…5) or propranolol (Fig. 6) intravenously, starting 30 min before the bout and ending at 60 min of recovery (35,36). With phentolamine (36), the importance of the usual islet ␣-receptor effect of inhibiting insulin secretion during exercise (2,3) is clearly illustrated by the threefold increase in insulin (Fig.…”

Four grams of glucose

“…Attempts to directly assess a role for catecholamines in stimulating endogenous glucose production during high-intensity exercise (Ͼ80% maximum O 2 uptake) in humans have also been negative (43,49,59,82,83). This is not to say that other factors such as IL-6 (23) or an as yet undefined regulator do not play some role.…”