Plasma sulpho-conjugated catecholamine dynamics up to 8 h after 60-min exercise at 50% and 70% maximal oxygen uptakes

Evaluation of stress responses to interval training at low and moderate altitudes

PURPOSE

The purpose of the present field study was to explore whether extensive interval training (IT) performed with a similar behavior of blood lactate (LA) at an altitude of 1800 m (ALT) and near sea level (SL) goes along with a comparable hormonal, metabolic, and acute phase response in highly trained endurance athletes.

METHODS

Twelve distance runners (VO2 64.6 +/- 6.9 mL.kg(-1) ) performed IT (10 x 1000 m, 2-min rest) at SL with a running velocity (V) corresponding to 112% of the individual anaerobic threshold (IAT). After an acclimatization period of 7 d, IT was repeated with a lower V (107% IAT) at ALT. Blood samples were drawn at rest, 0, 0.3, 3, and 24 h after IT. LA during IT was similar at SL and ALT (5.4 +/- 1.3/5.3 +/- 1.2 mmol.L(-1)), whereas HR tended to be higher at SL.

RESULTS

Postexercise rises in plasma noradrenaline (NA), NA sulfate, adrenaline, glucose, interleukin-6 (IL-6), and neutrophils were significantly more pronounced at ALT. The increase of cortisol and human growth hormone showed an insignificant trend toward higher values at ALT. A slight but significant increase of plasma erythropoietin was only apparent after IT at ALT. No differences between either condition were observed for exercise-related changes in free fatty acids, IL-8, lympho-, or monocyte counts.

CONCLUSIONS

In spite of a matched accumulation pattern of LA between ALT and N, stress responses, such as sympathetic activation and hepatic glucose release, still appear to be greater at ALT. This additional impact of moderate ALT on the stress response to IT should be taken into account if repeated training sessions are performed within a short period of time.

Sympathetic activity and the heterogenous blood pressure response to exercise training in hypertensives

To test whether changes in sympathetic nervous system (SNS) activity or insulin sensitivity contribute to the heterogeneous blood pressure response to aerobic exercise training, we used compartmental analysis of [3H]norepinephrine kinetics to determine the extravascular norepinephrine release rate (NE2) as an index of systemic SNS activity and determined the insulin sensitivity index (S(I)) by an intravenous glucose tolerance test, before and after 6 mo of aerobic exercise training, in 30 (63 +/- 7 yr) hypertensive subjects. Maximal O2 consumption increased from 18.4 +/- 0.7 to 20.8 +/- 0.7 ml x kg(-1) x min(-1) (P = 0.02). The average mean arterial blood pressure (MABP) did not change (114 +/- 2 vs. 114 +/- 2 mmHg); however, there was a wide range of responses (-19 to +17 mmHg). The average NE2 did not change significantly (2.11 +/- 0.15 vs. 1.99 +/- 0.13 microg x min(-1) x m(-2)), but there was a significant positive linear relationship between the change in NE2 and the change in MABP (r = 0.38, P = 0.04). S(I) increased from 2.81 +/- 0.37 to 3.71 +/- 0.42 microU x 10(-4) x min(-1) x ml(-1) (P = 0.004). The relationship between the change in S(I) and the change in MABP was not statistically significant (r = -0.03, P = 0.89). When the changes in maximal O2 consumption, percent body fat, NE2, and S(I) were considered as predictors of the change in MABP, only NE2 was a significant independent predictor. Thus suppression of SNS activity may play a role in the reduction in MABP and account for a portion of the heterogeneity of the MABP response to aerobic exercise training in older hypertensive subjects.

Circuit weight training and its effects on excess postexercise oxygen consumption

OBJECTIVE

There is a paucity of research concerning energy expenditure during and after circuit weight training (CWT). There is evidence that duration of rest between sets affects metabolic responses to resistive exercise. The purpose of the study was to determine the effect of rest-interval duration upon the magnitude of 1 h of excess postexercise oxygen consumption (EPOC).

METHODS

Seven healthy men completed two randomized circuit weight training sessions using 20-s and 60-s rest intervals (20 RI, 60 RI). Sessions included two circuits of eight upper and lower body resistive exercises in which 20 repetitions were performed at 75% of a previously determined 20 repetition maximum.

RESULTS

The 1 h EPOC of 10.3 +/- 0.57 L for the 20 RI session was significantly higher than 7.40 +/- 0.39 L for the 60 RI session. The net caloric expenditure during 1 h of recovery from the 20 RI session was significantly higher than that of the 60 RI session (51.51 +/- 2.84 vs 37.00 +/- 1.97 kcal); however, total gross energy expenditure (exercise + 1 h recovery) was significantly greater for the 60 RI protocol (277.23 kcal) than the 20 RI protocol (242.21 kcal).

CONCLUSION

Data demonstrate that shortening the rest interval duration will increase the magnitude of 1 h EPOC from CWT; however, the exercise + recovery caloric costs from CWT are slightly greater for a longer rest interval duration protocol. These data suggest that total caloric cost be taken into account for CWT.

Sources and physiological significance of plasma dopamine sulfate

Dopamine in the circulation occurs mainly as dopamine sulfate, the sources and physiological significance of which have been obscure. In this study, plasma concentrations of dopamine sulfate were measured after a meal, after fasting for 4 days, and during i.v. L-DOPA, nitroprusside, or trimethaphan infusion in volunteers; after dopamine infusion in patients with L-aromatic-amino-acid decarboxylase deficiency; in arterial and portal venous plasma of gastrointestinal surgery patients; and in patients with sympathetic neurocirculatory failure. Meal ingestion increased plasma dopamine sulfate by more than 50-fold; however, prolonged fasting decreased plasma dopamine sulfate only slightly. L-DOPA infusion produced much larger increments in dopamine sulfate than in dopamine; the other drugs were without effect. Patients with L-aromatic amino acid decarboxylase deficiency had decreased dopamine sulfate levels, and patients with sympathetic neurocirculatory failure had normal levels. Decarboxylase-deficient patients undergoing dopamine infusion had a dopamine sulfate/dopamine ratio about 25 times less than that at baseline in volunteers. Surgery patients had large arterial-portal venous increments in plasma concentrations of dopamine sulfate, so that mesenteric dopamine sulfate production accounted for most of urinary dopamine sulfate excretion, a finding consistent with the localization of the dopamine sulfoconjugating enzyme to gastrointestinal tissues. The results indicate that plasma dopamine sulfate derives mainly from sulfoconjugation of dopamine synthesized from L-DOPA in the gastrointestinal tract. Both dietary and endogenous determinants affect plasma dopamine sulfate. The findings suggest an enzymatic gut-blood barrier for detoxifying exogenous dopamine and delimiting autocrine/paracrine effects of endogenous dopamine generated in a "third catecholamine system."

Adrenergic control of post-exercise metabolism

After strenuous exercise there is a sustained increase in resting O2 consumption. The magnitude and duration of the excess post-exercise O2 consumption (EPOC) is a function of exercise intensity and exercise duration. Some of the mechanisms underlying the rapid EPOC component (<1 h) are well defined, while the mechanisms causing the prolonged EPOC component (>1 h) are not fully understood. It has been suggested that beta-adrenergic stimulation is of importance for the prolonged component. There is an increased level of plasma adrenaline and noradrenaline during exercise, and it is shown that catecholamines stimulate energy expenditure through beta-adrenoceptors. After exercise an increased fat oxidation and an increased rate of triglyceride fatty acid (TG-FA) cycling may account for a significant part of the prolonged EPOC component. These processes may be stimulated by catecholamines. However, the return of plasma concentration of catecholamines to resting levels after exercise is more rapid than the return of O2 uptake. But plasma concentration of catecholamines may be an insensitive indicator of sympathetic activity, since the clearance rate of catecholamines is high. Also, the sensitivity to catecholamines may be increased after exercise. A decreased post-exercise O2 uptake has been shown when beta-blockade is administered in dogs before the exercise bout. In a pilot study in humans, administration of beta-antagonist after exercise did not seem to change EPOC.