Generation of growth hormone pulsatility in women: evidence against somatostatin withdrawal as pulse initiator

1  Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Michigan and Veterans Affairs Medical Center, Ann Arbor, Michigan 48109; 2  Division of Endocrinology and Metabolism, Department of Internal Medicine, Tulane University, New Orleans, Louisiana 70112; and 3  N...

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Published in:American journal of physiology: endocrinology and metabolism 2001-03, Vol.280 (3), p.E489-E495
Main Authors: Dimaraki, Eleni V, Jaffe, Craig A, Demott-Friberg, Roberta, Russell-Aulet, Mary, Bowers, Cyril Y, Marbach, Peter, Barkan, Ariel L
Format: Article
Language:English
Subjects:
Aged
Body Mass Index
Female
Growth Hormone-Releasing Hormone - pharmacology
Hormones - administration & dosage
Hormones - blood
Human Growth Hormone - secretion
Humans
Hypothalamus - secretion
Luminescent Measurements
Middle Aged
Octreotide - administration & dosage
Octreotide - blood
Oligopeptides - pharmacology
Periodicity
Postmenopause
Somatostatin - secretion
Thyrotropin - blood
Thyrotropin-Releasing Hormone - pharmacology
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Summary:1  Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Michigan and Veterans Affairs Medical Center, Ann Arbor, Michigan 48109; 2  Division of Endocrinology and Metabolism, Department of Internal Medicine, Tulane University, New Orleans, Louisiana 70112; and 3  Novartis Pharma Ltd., CH-4002 Basel, Switzerland To test whether endogenous hypothalamic somatostatin (SRIH) fluctuations are playing a role in the generation of growth hormone (GH) pulses, continuous subcutaneous octreotide infusion (16 µg/h) was used to create constant supraphysiological somatostatinergic tone. Six healthy postmenopausal women (age 67 ± 3 yr, body mass index 24.7 ± 1.2 kg/m 2 ) were studied during normal saline and octreotide infusion providing stable plasma octreotide levels of 2,567 ± 37 pg/ml. Blood samples were obtained every 10 min for 24 h, and plasma GH was measured with a sensitive chemiluminometric assay. Octreotide infusion suppressed 24-h mean GH by 84 ± 3% ( P  = 0.00026), GH pulse amplitude by 90 ± 3% ( P  = 0.00031), and trough GH by 54 ± 5% ( P  = 0.0012), whereas GH pulse frequency remained unchanged. The response of GH to GH-releasing hormone (GHRH) was not suppressed, and the GH response to GH-releasing peptide-6 (GHRP-6) was unaffected. We conclude that, in women, periodic declines in hypothalamic SRIH secretion are not the driving force of endogenous GH pulses, which are most likely due to episodic release of GHRH and/or the endogenous GHRP-like ligand. growth hormone-releasing peptide; humans; pituitary; hypothalamic control
ISSN:0193-1849
1522-1555
DOI:10.1152/ajpendo.2001.280.3.e489