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Growth Hormone Tips

Growth hormone, also known as somatotropin, is a protein hormone of about 190 Growth Hormone Tipsamino acids that is synthesized and secreted by cells called somatotrophs in the anterior pituitary.

It is a major participant in control of several complex physiologic processes, including growth and metabolism. Growth hormone is also of considerable interest as a drug used in both humans and animals.

Last Updated - 7th November 2005

Physiologic Effects of Growth Hormone

A critical concept in understanding growth hormone activity is that it has two distinct types of effects:

Effects on Growth

Growth is a very complex process, and requires the coordinated action of several hormones. The major role of growth hormone in stimulating body growth is to stimulate the liver and other tissues to secrete IGF-I. IGF-I stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth. Growth hormone does seem to have a direct effect on bone growth in stimulating differentiation of chondrocytes.

IGF-I also appears to be the key player in muscle growth. It stimulates both the differentiation and proliferation of myoblasts. It also stimulates amino acid uptake and protein synthesis in muscle and other tissues.

Metabolic Effects

Growth hormone has important effects on protein, lipid and carbohydrate metabolism. In some cases, a direct effect of growth hormone has been clearly demonstrated, in others, IGF-I is thought to be the critical mediator, and some cases it appears that both direct and indirect effects are at play.

Control of Growth Hormone Secretion

Production of growth hormone is modulated by many factors, including stress, exercise, nutrition, sleep and growth hormone itself. However, its primary controllers are two hypothalamic hormones and one hormone from the stomach:

Growth hormone secretion is also part of a negative feedback loop involving IGF-I. High blood levels of IGF-I lead to decreased secretion of growth hormone not only by directly suppressing the somatotroph, but by stimulating release of somatostatin from the hypothalamus.

Growth hormone also feeds back to inhibit GHRH secretion and probably has a direct (autocrine) inhibitory effect on secretion from the somatotroph.

Integration of all the factors that affect growth hormone synthesis and secretion lead to a pulsatile pattern of release. Basal concentrations of growth hormone in blood are very low. In children and young adults, the most intense period of growth hormone release is shortly after the onset of deep sleep.

Disease States

States of both growth hormone deficiency and excess provide very visible testaments to the role of this hormone in normal physiology. Such disorders can reflect lesions in either the hypothalamus, the pituitary or in target cells. A deficiency state can result not only from a deficiency in production of the hormone, but in the target cell's response to the hormone.

Clinically, deficiency in growth hormone or receptor defects are as growth retardation or dwarfism. The manifestation of growth hormone deficiency depends upon the age of onset of the disorder and can result from either heritable or acquired disease.

The effect of excessive secretion of growth hormone is also very dependent on the age of onset and is seen as two distinctive disorders:

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Pharmaceutical and Biotechnological Uses of Growth Hormone

In years past, growth hormone purified from human cadaver pituitaries was used to treat children with severe growth retardation. More recently, the virtually unlimited supply of recombinant growth hormone has lead to several other applications to human and animal populations.

Another application of growth hormone in animal agriculture is treatment of growing pigs with porcine growth hormone. Such treatment has been demonstrated to significantly stimulate muscle growth and reduce deposition of fat.

Growth Hormone and Aging

Normal Changes in the Growth Hormone Axis with Aging

GH Replacement Therapy in GH-deficient Adults

GH Therapy in the Elderly

In 1990, considerable excitement was generated from a report by Rudman and colleagues which described wonderful effects of GH treatment in a small group of elderly men. These volunteers, who ranged in age from 61 to 81 years, showed increased lean body and bone mass, decreased fat mass and, perhaps most dramatically, restoration of skin thickness to that typical of a 50-year-old.

The study cited above and a handful of others have provided an initial understanding of the benefits, limitations and risks of sustained (6 to 12 month) GH supplementation in elderly men and women. A consistent finding in these investigations was a high incidence of adverse side effects - edema, fluid retention and carpal tunnel syndrome - which necessitated reductions in GH dose of cessation of treatment. GH treatment consistently induced an increase in serum IGF-1, a decrease in fat mass and increase in lean mass.

The effects on fat and lean masses may be viewed as positive effects, but, at the end of the day, it has to be asked whether GH treatment improved functioning in the elderly. In the studies in which function was objectively assessed, GH treatment did not improve cognitive function, and, despite the effects on lean body mass, was not any more effective than exercise alone in promoting strength. Long-term GH therapy in elderly postmenopausal women lead to significant increases in bone mineral density, but these increases were less than what is routinely achieved with estrogen replacement. While it must be acknowledged that a relatively small number of elderly patients have been treated for prolonged periods with GH, the controlled trials conducted thus far do not support is efficacy in aleviating age-related deficits in cognitive or somatic function.

Another indication of potentially serious side effects of GH therapy in adults, including the elderly, has been provided by controlled clinical trials that assessed the utility of human GH treatment in critical illness, where endogenous GH secretion is typically suppressed. GH therapy was anticipated to attenuate the catabolic effects of illness and thereby decrease duration of hospitalization. The results of several clinical trials involving hundreds of patients, demonstrated a significant increase in mortality associated with high doses of GH. Additionally, those patients treated with GH that survived had longer periods of intensive care and hospitalization than those receiving placebos.

Disclaimer: The Growth Hormone Tips / Information presented and opinions expressed herein are those of the authors and do not necessarily represent the views of Tips And Treats . com and/or its partners.

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