Abstract
Inhibition of adipose tissue lipolysis, leading to a reduced availability of non-esterified
fatty acids for energy production in the active skeletal muscles, may be involved
in the impairment of endurance exercise capacity after administration of a beta-adrenoceptor
blocking agent. The effect of increasing the availability of plasma NEFA during exercise
after beta-blocker administration was studied. In a double-blind, randomized cross-over
study 12 healthy volunteers were treated for 14 days with placebo, atenolol, and propranolol.
On the 7th and 14th day of each treatment period an endurance exercise test at 70%
of maximal aerobic power until exhaustion was performed while a continuous infusion
of saline or triglycerides (Intralipid) + heparin was administered. Endurance time
was reduced by 11% (n.s.) during atenolol and 40% (p<0.01) during propranolol. Intralipid
administration had no statistically significant effect on endurance in any treatment.
Plasma NEFA and glycerol concentrations were elevated above control levels during
Intralipid infusion, plasma glucose and lactate concentrations were unaffected. These
results suggest that reduced availability of NEFA is not a major factor in the reduction
of endurance performance during beta-adrenoceptor blockade, although an effect of
beta-blockade on NEFA membrane transport cannot be excluded.
Key words
Beta-adrenoceptor blockade - exercise - lipolysis - energy metabolism - non-esterified
fatty acids
