Beta-adrenergic blockade alters whole-body leucine metabolism in humans.
This study examined the effects of a nonselective beta-blocking agent on whole-body leucine metabolism in humans. Five normal, healthy subjects (4 male, 1 female) underwent a 6-h primed, constant-rate infusion of L-[1-13C]leucine after 5 days of twice daily oral use of 80 mg propranolol and a placebo. Leucine turnover was determined by tracer dilution and leucine oxidation by 13C enrichment of the expired CO2. Propranolol decreased the total daily energy expenditure from 1,945 +/- 177.5 to 1,619 +/- 92.5 kcal/day (P less than 0.05). A fasting associated decrease in blood glucose and an attenuated rise in free fatty acids and ketones were observed during beta-blockade. Propranolol also increased plasma leucine concentrations (73.1 +/- 8.7 to 103.4 +/- 7.3 mumol/l; P less than 0.05) and leucine oxidation (13.2 +/- 1.2 to 17.1 +/- 1.3 mumol.kg-1.h-1; P less than 0.05), although leucine turnover was not significantly altered (100.5 +/- 7.3 vs. 126.0 +/- 12.3 mumol.kg-1.h-1). In addition, the urinary urea nitrogen-to-creatinine ratio was greater during propranolol administration (0.24 +/- 0.04 vs. 0.34 +/- 0.02 mol/g; P less than 0.05). These data suggest that the beta-adrenergic system plays a role in the modulation of whole-body leucine metabolism in humans. Whether these changes are the result of a direct effect on skeletal muscle or an indirect effect mediated by altering the fuel supply to skeletal muscle cannot be discriminated by the present study.
Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109.
L S
LS
Lamont
D G
DG
Patel
S C
SC
Kalhan
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood; D007930:Leucine / Q000097:blood / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D011433:Propranolol / Q000494:pharmacology*
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006885:Hydroxybutyrates; D011433:Propranolol; D007930:Leucine; D009638:Norepinephrine; D004837:Epinephrine