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J Clin Endocrinol Metab. 2008 Jul;93(7):2755-9. doi: 10.1210/jc.2008-0079. Epub 2008 Apr 15.

Role of growth hormone in regulating lipolysis, proteolysis, and hepatic glucose production during fasting.

Author information

1
Division of Metabolism, Endocrinology, and Diabetes, 3920 Taubman Center, University of Michigan Medical Center, Ann Arbor, MI 48109-5354, USA.

Abstract

CONTEXT:

Fasting is associated with suppressed insulin and augmented GH secretion. The involvement of each mechanism in the regulation of fuel mobilization during fasting is unknown.

OBJECTIVE:

To ascertain the role of GH in the regulation of the rates of lipolysis, proteolysis, and hepatic glucose production (HGP) during the physiological daily feed/fast cycle and after 2 d of complete fasting, we used a model of selective GH suppression by the administration of GHRH receptor antagonist (GHRH-A).

DESIGN AND SETTING:

We conducted an open label in-patient study in the General Clinical Research Center at the University of Michigan.

PARTICIPANTS:

Six healthy, nonobese volunteers participated.

MAIN OUTCOME MEASURES:

We assessed 24-h plasma GH concentration and rates of lipolysis, proteolysis, and HGP using stable isotope techniques after an overnight fast and after 2 d of fasting.

RESULTS:

GHRH-A suppressed plasma GH by about 65% during the fed state (P = 0.015) but did not alter the rates of lipolysis, proteolysis, or HGP. Fasting for 2 d suppressed plasma insulin concentration by about 80% and elevated plasma GH about 4-fold (both P < 0.01). This was accompanied by a doubling in the rate of lipolysis, an approximately 40% increase in proteolysis, and an approximately 30% decline in HGP (all P < 0.05). Preventing the fasting-induced increase in GH with GHRH-A largely abolished the increase in the rate of lipolysis. GHRH-A also augmented the fasting-induced reduction in HGP but did not alter proteolysis.

CONCLUSIONS:

Endogenous GH plays a very limited metabolic role during the daily feed/fast cycle but is essential for the increased lipolytic rate found with more prolonged fasting.

PMID:
18413425
PMCID:
PMC2453052
DOI:
10.1210/jc.2008-0079
[Indexed for MEDLINE]
Free PMC Article

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