The decisive role of free fatty acids for protein conservation during fasting in humans with and without growth hormone.
During fasting, a lack of GH increases protein loss by close to 50%, but the underlying mechanisms remain uncertain. The present study tests the hypothesis that the anabolic actions of GH depend on mobilization of lipids. Seven normal subjects were examined on four occasions during a 37-h fast with infusion of somatostatin, insulin, and glucagon for the final 15 h: 1) with GH replacement, 2) with GH replacement and antilipolysis with acipimox, 3) without GH and with antilipolysis, and 4) with GH replacement, antilipolysis, and infusion of intralipid. Urinary urea excretion, serum urea concentrations, and muscle protein breakdown (assessed by labeled phenylalanine) increased by almost 50% during fasting with suppression of lipolysis. Addition of GH during fasting with antilipolysis did not influence indexes of protein degradation, whereas restoration of high FFA levels regenerated proportionally low concentrations of urea and decreased whole body protein degradation (phenylalanine to tyrosine conversion) by 10-15%, but failed to affect muscle protein metabolism. Thus, the present data provide strong evidence that FFA are important protein-sparing agents during fasting. The finding that inhibition of lipolysis eliminates the ability of GH to restrict fasting protein loss indicates that stimulation of lipolysis is the principal protein-conserving mechanism of GH.
Nørrelund
Helene
H
Medical Department M (Endocrinology and Diabetes), Aarhus University Hospital, DK-8000 Aarhus C, Denmark. helenenorrelund@dadlnet.dk
Nair
K Sreekumaran
KS
Nielsen
Steen
S
Frystyk
Jan
J
Ivarsen
Per
P
Jørgensen
Jens Otto Lunde
JO
Christiansen
Jens Sandahl
JS
Møller
Niels
N
D000328:Adult; D000596:Amino Acids / Q000097:blood; D005215:Fasting / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D013006:Growth Hormone / Q000494:pharmacology*; D006493:Heparin / Q000097:blood; D006727:Hormone Antagonists / Q000494:pharmacology; D019382:Human Growth Hormone / Q000097:blood* / Q000502:physiology; D006801:Humans; D000960:Hypolipidemic Agents / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D017551:Microdialysis; D018482:Muscle, Skeletal / Q000378:metabolism; D010649:Phenylalanine / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology; D013004:Somatostatin / Q000494:pharmacology; D014280:Triglycerides / Q000097:blood / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism; D014508:Urea / Q000652:urine
D000596:Amino Acids; D005230:Fatty Acids, Nonesterified; D006727:Hormone Antagonists; D000960:Hypolipidemic Agents; D011506:Proteins; D011719:Pyrazines; D014280:Triglycerides; D019382:Human Growth Hormone; D014443:Tyrosine; D010649:Phenylalanine; D013004:Somatostatin; D014508:Urea; D013006:Growth Hormone; D006493:Heparin; C027696:acipimox