Autoregulation of growth hormone secretion in normal subjects |
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Authors: | T C Hagen A M Lawrence L Kirsteins |
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Affiliation: | 1. Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia;2. Centre for Sport Research, School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia;1. The Francis Crick Institute, London, UK;2. Brain Health Research Institute and Department of Biological Sciences, Kent State University, Kent, OH, USA;1. McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University, Baltimore, MD, United States;2. Department of Surgery, Johns Hopkins University, Baltimore, MD, United States;3. Genomic Programming of Beta-Cells Laboratory, Institut d’Investigacions Biomèdiques August Pi i Sunyer, CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Barcelona, Spain;1. Doctor of Physical Therapy, Duke University, 2200 West Main Street, Suite B-230, Durham, NC 27705, United States;2. Florida State University, 9705 Waters Meet Drive, Tallahassee, FL 32312, United States;1. Department of Clinical Pharmacology and Medicine, College of Medicine, Mustansiriyah University, Baghdad, Iraq;2. Department of Applied Science, University of Technology, Iraq |
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Abstract: | Studies performed in animals have demonstrated fairly definitely that raised growth hormone levels exert a negative feedback or autoregulatory effect on further pituitary growth hormone release. Similar evidence was sought in normal human volunteers. Growth hormone levels were raised either by introducing a provocative stimulus, exercise or arginine, or by infusing human growth hormone at a constant rate. When circulating levels of growth hormone were raised by a measured exercise stimulus or by an arginine infusion, a second stimulus introduced in tandem failed to cause a further rise, and circulating growth hormone levels dropped to baseline. This was not due to pituitary growth hormone exhaustion, since combining the stimuli produced a far greater growth hormone release than either stimulus alone. Normal release in response to arginine or exercise could be demonstrated if a 30-min pause was allowed between tests. Similarly, when growth hormone levels were raised by injections or with a constant growth hormone infusion, no response to exercise or to arginine was seen. Thus, in man, as in animals, it appears that circulating levels of growth hormone do exert an autoregulatory influence on the secretory activity of either the hypothalamus or the pituitary. Abnormal variations in the threshold sensitivity to this feedback could account for certain disturbances of pituitary growth hormone release, in particular acromegaly. |
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