Abstract
The β2-adrenergic system is an important regulator of human adipose tissue lipolysis. Polymorphisms that result in amino acid substitutions in the β2-adrenergic receptor have been reported to alter lipolysis. We hypothesized that variations in the amino acid at position 16 of the β2-adrenergic receptor would result in different lipolytic responses to intravenous epinephrine and exercise. 17 volunteers homozygous for glycine at position 16 (Gly/Gly, nine female) and 16 volunteers homozygous for arginine at position 16 (Arg/Arg, eight female) of the β2-adrenergic receptor participated in this study. On one study day participants received infusions of epinephrine at submaximal (5 ng kg(-1) min(-1)) and maximal (40 ng kg(-1) min(-1)) lipolytic doses. The other study day volunteers bicycled for 90 min at 50-60% of maximum oxygen consumption (VO2max). [9,10-(3)H] Palmitate was infused both days to measure free fatty acid - palmitate kinetics. Oxygen consumption was measured using indirect calorimetry. Palmitate release rates in response to epinephrine and exercise were not different in the Gly/Gly and Arg/Arg participants. The only statistically significant difference we observed was a lesser ΔVO2 in Arg/Arg volunteers in response to the submaximal epinephrine infusion. The polymorphisms resulting in Arg/Arg and Gly/Gly at position 16 of the β2-adrenergic receptor do not result in clinically meaningful differences in lipolysis responses to epinephrine or submaximal exercise.