Activation of alpha2-adrenergic receptors blunts epinephrine-induced lipolysis in subcutaneous adipose tissue during a hyperinsulinemic euglycemic clamp in men.
The aim of this study was to investigate whether hyperinsulinemia modifies adrenergic control of lipolysis, with particular attention paid to the involvement of antilipolytic alpha2-adrenergic receptors (AR). Eight healthy male subjects (age: 23.9 +/- 0.9 yr; body mass index: 23.8 +/- 1.9) were investigated during a 6-h euglycemichyperinsulinemic clamp and in control conditions. Before and during the clamp, the effect of graded perfusions of isoproterenol (0.1 and 1 microM) or epinephrine (1 and 10 microM) on the extracellular glycerol concentration in subcutaneous abdominal adipose tissue was evaluated by using the microdialysis method. Both isoproterenol and epinephrine induced a dose-dependent increase in extracellular glycerol concentration when infused for 60 min through the microdialysis probes before and during hours 3 and 6 of the clamp. The catecholamine-induced increase was significantly lower during the clamp than before it, with the inhibition being more pronounced in hour 6 of the clamp. Isoproterenol (1 microM)-induced lipolysis was reduced by 28 and 44% during hours 3 and 6 of the clamp, respectively, whereas the reduction of epinephrine (100 microM)-induced lipolysis was significantly greater (by 63 and 70%, P < 0.01 and P < 0.04, respectively) during the same time intervals. When epinephrine was infused in combination with 100 microM phentolamine (a nonselective alpha-AR antagonist), the inhibition of epinephrine (10 microM)-induced lipolysis was only of 19 and 40% during hours 3 and 6 of the clamp, respectively. The results demonstrate that, in situ, insulin counteracts the epinephrine-induced lipolysis in adipose tissue. The effect involves 1) reduction of lipolysis stimulation mediated by the beta-adrenergic pathway and 2) the antilipolytic component of epinephrine action mediated by alpha2-ARs.
Stich
Vladimir
V
Department of Sports Medicine, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
Pelikanova
Tereza
T
Wohl
Petr
P
Sengenès
Coralie
C
Zakaroff-Girard
Alexia
A
Lafontan
Max
M
Berlan
Michel
M
D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism*; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage; D000318:Adrenergic beta-Agonists / Q000008:administration & dosage; D000328:Adult; D004837:Epinephrine / Q000008:administration & dosage*; D015309:Glucose Clamp Technique; D005990:Glycerol / Q000097:blood; D006801:Humans; D006946:Hyperinsulinism / Q000378:metabolism; D007328:Insulin / Q000097:blood; D007545:Isoproterenol / Q000008:administration & dosage; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology; D008297:Male; D017551:Microdialysis; D010646:Phentolamine / Q000008:administration & dosage; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D040521:Subcutaneous Tissue / Q000187:drug effects / Q000378:metabolism; D013566:Sympathomimetics / Q000008:administration & dosage*
D000317:Adrenergic alpha-Antagonists; D000318:Adrenergic beta-Agonists; D007328:Insulin; D018341:Receptors, Adrenergic, alpha-2; D013566:Sympathomimetics; D007545:Isoproterenol; D005990:Glycerol; D004837:Epinephrine; D010646:Phentolamine