Investigation of the effects of beta-2 stimulation on free fatty acids in man

Exercise performance after salbutamol inhalation in non-asthmatic, non-athlete individuals: a randomised, controlled, cross-over trial

Background

Asthma is a frequent diagnosis in competitive sports, and inhaled β₂-agonists are commonly used by athletes. Although inhaled β₂-agonists do not seem to improve performance in athletes, it has remained uncertain whether they can increase exercise performance in non-athletes.

Objective

To investigate the effect of inhaled β₂-agonists on exercise performance in healthy non-athlete individuals.

Methods

In a double-blinded, placebo-controlled, cross-over trial, healthy, non-asthmatic, non-athlete individuals were randomised to inhalation of either 900 µg of salbutamol or placebo. Cardiopulmonary exercise testing, dynamic spirometry and impulse oscillometry were performed. The primary outcome was the effect from salbutamol on peak oxygen uptake, whereas secondary outcomes were breathing reserve and ventilation efficiency, and workload, heart rate, breath rate and minute ventilation at peak exercise under influence of salbutamol.

Results

A total of 36 healthy subjects with a mean age of 26±5 years were included. Salbutamol had no effect on peak oxygen uptake compared with placebo, 46.8±1.3 mL/kg/min versus 46.6±1.2 mL/kg/min, p=0.64. Salbutamol had no effect on workload, p=0.20, heart rate, p=0.23, breath rate, p=0.10, or minute ventilation, p=0.26, at peak exercise compared with placebo. Salbutamol lowered oxygen uptake, p=0.04, and workload, p=0.04, at anaerobic threshold compared with placebo. Forced expiratory volume in 1 s, 116%±13% of predicted, and peak expiratory flow, 122%±16% of predicted, increased after inhalation of salbutamol compared with placebo; 109%±13% and 117%±17%, respectively, p<0.01. Breathing reserve was found to be higher, 22%±2%, after salbutamol inhalation than after placebo, 16%±2%, p<0.01.

Conclusion

Inhaled salbutamol did not improve peak oxygen uptake in healthy, non-asthmatic, non-athlete individuals compared with placebo.

Trial registration number

NCT02914652.

Adrenergic control of lipolysis in women compared with men

Data suggest women are more sensitive to the lipolytic action of epinephrine compared with men while maintaining similar glucoregulatory effects (Horton et al. J Appl Physiol 107: 200-210, 2009). This study aimed to determine the specific adrenergic receptor(s) that may mediate these sex differences. Lean women (n = 14) and men (n = 16) were studied on 4 nonconsecutive days during the following treatment infusions: saline (S: control), epinephrine [E: mixed β-adrenergic (lipolytic) and α2-adrenergic (antilipolytic) stimulation], epinephrine + phentolamine (E + P: mixed β-adrenergic stimulation only), and terbutaline (T: selective β2-adrenergic stimulation). Tracer infusions of glycerol, palmitate, and glucose were administered to determine systemic lipolysis, free fatty acid (FFA) release, and glucose turnover, respectively. Following basal measurements, substrate and hormone concentrations were measured in all subjects over 90 min of treatment and tracer infusion. Women had greater increases in glycerol and FFA concentrations with all three hormone infusions compared with men (P < 0.01). Glycerol and palmitate rate of appearance (Ra) and rate of disappearance (Rd) per kilogram body weight were greater with E infusion in women compared with men (P < 0.05), whereas no sex differences were observed with other treatments. Glucose concentration and kinetics were not different between sexes with any infusion. In conclusion, these data support the hypothesis that the greater rate of lipolysis in women with infusion of E was likely due to lesser α2 antilipolytic activation. These findings may help explain why women have greater lipolysis and fat oxidation during exercise, a time when epinephrine concentration is elevated.

Addition of tiotropium to formoterol improves inspiratory muscle strength after exercise in COPD

BACKGROUND

The addition of tiotropium bromide (TIO) to formoterol fumarate (FOR) improves exercise performance in patients with chronic obstructive pulmonary disease (COPD). In this study, we test the hypothesis that the addition of TIO to FOR may improve respiratory muscle performance and oxygen uptake kinetics after exercise in patients with COPD.

METHODS

Thirty eight patients with COPD were randomized to a 2 week treatment with FOR 12 μg twice a day plus TIO 18 μg once a day (FOR + TIO) or FOR 12 μg twice a day plus placebo (FOR + PLA) once a day, using a double-blind crossover design. Inspiratory muscle. Strength was measured before, immediately after, as well as 2, 5, and 10 min during recovery of exercise. Time to limit of tolerance on a constant work load exercise test and oxygen uptake kinetics during recovery were evaluated before and after intervention.

RESULTS

Only FOR + TIO improved resting (63 ± 10 cm to 84 ± 11 cmH(2)O) and post-exercise (49 ± 7 cm to 84 ± 11 cmH(2)O) maximal inspiratory pressure. Time to limit of tolerance on the constant work load test was increased by FOR + PLA and by FOR + TIO, but the size of the increment was significantly larger with FOR + TIO (40.7 ± 7.6% vs. 84.5 ± 8.2%; p < 0.05). Only FOR + TIO improved oxygen uptake kinetics during recovery (69 ± 21 to 60 ± 18 s). The improvement in maximal inspiratory pressure (0.78, p < 0.001) and in oxygen uptake kinetics (-0.91, p < 0.001) correlated with the change in time to the limit of tolerance.

CONCLUSIONS

The addition of TIO to FOR improves inspiratory muscle strength and oxygen uptake kinetics after exercise in COPD patients.

Selective versus nonselective β-adrenergic receptor blockade in chronic heart failure: differential effects on myocardial energy substrate utilization

BACKGROUND

Non-selective and selective beta-blockers have been shown to improve outcomes in chronic heart failure (CHF). Recent data suggests the non-selective beta-blockers have a more favourable effect on outcomes than beta(1)-selective agents. We sought to examine the differential effects of non-selective versus selective beta-blockade on myocardial substrate utilization in patients with CHF.

METHODS AND RESULTS

Twenty-two patients with CHF were randomised to the non-selective beta-blocker carvedilol or the selective beta-blocker metoprolol (double-blind). Measurement of hemodynamics, arterial and coronary sinus free fatty acid (FFA) and lactate levels, and cardiac norepinephrine spillover (CANESP) were made before and after 4 months of therapy. In the carvedilol group (n=11), there was a significant reduction in myocardial FFA uptake (0.12+/-0.02 to 0.1+/-0.02 mmol/l, P<0.03). By contrast, in the metoprolol group (n=11) there was no change in myocardial FFA extraction. Carvedilol therapy tended to increase myocardial lactate extraction (0.24+/-0.05 to 0.35+/-0.08 mmol/l, P=0.08) while metoprolol therapy resulted in a trend in the opposite direction (0.18+/-0.03 to 0.11+/-0.04 mmol/l, P=0.09). The change in lactate extraction in the carvedilol group was significantly different from that in the metoprolol group (+0.11+/-0.06 vs. -0.09+/-0.04 mmol/l, P<0.01). Carvedilol treatment caused a significant reduction in CANESP while metoprolol had a neutral effect (-95+/-27 vs. 25+/-42 pmol/min, carvedilol vs. metoprolol P<0.03).

CONCLUSION

Carvedilol treatment caused a 20% reduction in myocardial free fatty acid extraction while metoprolol had a neutral effect. These differences are most probably related to the differential effects of these two agents on efferent cardiac sympathetic activity and may be relevant to the reported differential effects of these drugs on clinical outcomes.

Lactic acidosis in status asthmaticus : three cases and review of the literature

Lactic acidosis is a frequent laboratory finding in patients with severe exacerbations of asthma. The pathogenesis of lactic acidosis in asthma is not well understood, but it has been presumed, by some, to be generated by fatiguing respiratory muscles. We herein report the cases of three patients with status asthmaticus and lactic acidosis despite pharmacologic muscle relaxation. No common etiologies were found for lactic acidosis that abated after bronchospasm improved and the intensity of pharmacologic therapies was reduced. We review the literature describing lactic acidosis with asthma and discuss mechanisms by which lactic acidosis may occur in patients with status asthmaticus.

Effects of short-term oral salbutamol administration on exercise endurance and metabolism

The present study examined whether oral short-term administration of salbutamol (Sal) modifies performance and selected hormonal and metabolic variables during submaximal exercise. Eight recreational male athletes completed two cycling trials at 80-85% peak O(2) consumption until exhaustion after either gelatin placebo (Pla) or oral Sal (12 mg/day for 3 wk) treatment, according to a double-blind and randomized protocol. Blood samples were collected at rest, after 5, 10, and 15 min, and at exhaustion to determine growth hormone (GH), cortisol, testosterone, triiodothyronine (T(3)), C peptide, free fatty acid (FFA), blood glucose, lactate, and blood urea values. Time of cycling was significantly increased after chronic Sal intake (Sal: 30.5 +/- 3.1 vs. Pla: 23.7 +/- 1.6 min, P < 0.05). No change in any variable was found before cycling except a decrease in blood urea concentration and an increase in T(3) after Sal that remained significant throughout the exercise test (P < 0.05). Compared with rest, exercise resulted in a significant increase in GH, cortisol, testosterone, T(3), FFAs, and lactate and a decrease in C peptide after both treatments with higher exercise FFA levels and exhaustion GH concentrations after Sal (P < 0.05). Sal but not Pla significantly decreased exercise blood glucose levels. From these data, short-term Sal intake did appear to improve performance during intense submaximal exercise with concomitant increase in substrate availability and utilization, but the exact mechanisms involved need further investigation.

Metabolic effects of beta 2-agonists

Catecholamines produce a number of biochemical changes most of which result from stimulation of beta 2-receptors. Interest in these metabolic effects has increased recently as a consequence of the concern over the relatively high mortality from acute asthma attacks. In this review the data on the impact of beta 2-agonists on glucose production, insulin release and lipolysis are presented. Thereafter the subject of hypokalaemia, the mechanism for its production by beta 2-agonists and its relevance to cardiac arrhythmias are considered in detail. Finally the fall in plasma magnesium and the possible role of beta 2-agonists in the production of lactic acidosis are discussed.

Assessment of beta-1 selectivity of bisoprolol and atenolol by means of their influence on the lipolytic response to an infusion of terbutaline

We have investigated the beta-1 selectivity of a new beta-blocker, Bisoprolol, by comparing its effect on lipolysis induced by intravenous terbutaline infusion with that of Atenolol. At a dose of 5 mg, Bisoprolol had virtually no beta-2 blocking activity as measured by free fatty acid (FFA) release during terbutaline infusion. At a dose of 10 mg, Bisoprolol had a small but statistically insignificant effect on FFA release similar to 50 mg Atenolol. At a dose of 20 mg, Bisoprolol had significant beta-2 blocking activity. At lower doses, therefore, Bisoprolol is a very selective beta-blocker.