Effect of increased plasma non-esterified fatty acid concentrations on endurance performance during beta-adrenoceptor blockade.

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.