The effect of propranolol on free fatty acid mobilization and resting metabolic rate

The role of the sympathetic nervous system in free fatty acid (FFA) mobilization was assessed in this study. FFA turnover rate using 1-14C-palmitic acid and metabolic rate by using indirect calorimetry were measured in ten white and 12 Pima Indian males after an overnight fast and during propranolol infusion (120 micrograms/kg fat-free mass [FFM] bolus and 1.2 micrograms/kg FFM/min). Baseline FFA turnovers were similar in both racial groups and decreased similarly following propranolol infusion (-16% +/- 4%; P less than .001, n = 22). This decrease was greater in more obese subjects (decrease in FFA turnover v % body fat, r = -.59, P less than .01, n = 22). Propranolol also induced an increase in lipid oxidation, which was more marked in the subjects with a high ratio of abdomen to thigh circumference (A/T ratio) (r = .63, P less than .01, n = 22). On average the resting metabolic rate (RMR) was unchanged during propranolol infusion, but individuals with lower A/T ratio had greater decreases in RMR than subjects with higher A/T ratio (r = .48, P less than .05). Assuming that the change in FFA turnover following beta-blockade is proportional to the role that the catecholamines (and therefore the sympathetic nervous system) play in mobilization of FFA, the greater fall in FFA turnover after propranolol infusion in more obese subjects suggests that they have a higher basal sympathetic activity. Furthermore, the lack of decrease in metabolic rate in response to beta-blockade in persons with a high A/T ratio could be the reflection of an even greater SNS activity in individuals with central obesity.