Peripheral sympathetic activity and anaerobic metabolism during muscular exercise in man
Cherchi, A.; Mercuro, G.; Montaldo, P.; Tocco, L.; Rivano, A.C.; Rossetti, Z.; Stefanini, E.; Bande, M.; Ruscazio, M.; Giua Marassi, P.P.
Cardiologia 32(3): 255-261
1987
ISSN/ISBN: 0393-1978 PMID: 3607795 Document Number: 301715
We examined 8 male volunteers (20-48 yr) during a maximal, progressive, upright bicycle exercise in order to correlate the peripheral sympathetic functional changes to the behaviour of metabolic parameters. Plasma levels of norepinephrine, epinephrine and 3,4-dihydroxyphenylacetic acid (DOPAC, a dopamine metabolite) and arterial lactate and pH were measured at sitting rest, at the end of 3 min work loads corresponding to 30, 50, 70, 90 e 100% .ovrhdot.VO2max and during the recovery (10 min). Blood lactate showed a slow and progressive increase until 70% .ovrhdot.VO2max (from 13.6 .+-. 1 to 33.9 .+-. 4 mg/100 ml, p < 0.05) and a very dramatic rise within 70 and 100% .ovrhdot.VO2max (76.3 .+-. 3, p < 0.001). Plasma norepinephrine level increase exhibited a similar diphasic time course (resting: 321 .+-. 53 pg/ml; 70% .ovrhdot.VO2max: 686 .+-. 59, p < 0.01; 100% .ovrhdot.VO2max: 1105 .+-. 77, p < 0.001). We found a significant correlation between VO2 and lactate (R = 0.94, p < 0.001), norepinephrine (R = 0.74, p < 0.001), epinephrine (R = 0.81, p < 0.001) and DOPAC (r = 0.58, p < 0.001) and between lactate and norepinephrine (r = 0.66, p < 0.001). Circulating DOPAC progressively increased during exercise (1.2 .+-. 0.1 mg/ml vs 0.9 .+-. 0.1, p < 0.05) and recovery (1.4 .+-. 0.1, p < 0.01). These data suggest that the dramatic increase in plasma norepinephrine at peak exercise would be a result of the metabolic changes occuring at this time. The anaerobic metabolism of peripheral tissues might be responsible for failure in norepinephrine reuptake and consequent rise in plasma norepinephrine free amount. The increase at peak exercise and during the recovering of DOPAC, expression of dopamine .beta.-hydroxilase exhaustion, seems to be consistent with this hypothesis.