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- Isaksson, Olle, 1943, et al.
(författare)
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GH and bone--experimental and clinical studies.
- 2000
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Ingår i: Endocrine journal. - 0918-8959. ; 47 Suppl, s. S9-16
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Tidskriftsartikel (refereegranskat)abstract
- GH increases bone formation both via a direct interaction with GH receptors on osteoblasts and via locally produced IGF-I (autocrine/paracrine action). GH deficiency results in decreased bone mass in both man and laboratory animals and treatment of GHD patients with GH for several months results in increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with normal GH secretion. Because of the short duration of GH-treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. The action of GH on bone metabolism in GHD adults is twofold: It stimulates both bone resorption and bone formation. A "Biphasic model" of GH action in bone remodeling has recently been proposed [1] (Fig. 2). According to this model the net effect of GH first results in a loss of bone mass, followed by a net increase in bone mass. The transition point occurs when bone formation proceeds at a higher rate than bone resorption. Taking all clinical studies of GH-treatment of GHD adults into account, it appears that the "transition point" occurs after approximately six months and that a net increase in bone mass usually is seen after 12-18 months of GH treatment. It should be emphasized that the "Biphasic model" of GH action in bone remodeling is proposed based on findings in GHD adults, and it remains to be clarified whether or not it is valid for subjects with normal GH secretion.
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| 2. |
- Ohlsson, Claes, 1965, et al.
(författare)
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Growth hormone and bone.
- 1998
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Ingår i: Endocrine reviews. - 0163-769X. ; 19:1, s. 55-79
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that GH is important in the regulation of longitudinal bone growth. Its role in the regulation of bone metabolism in man has not been understood until recently. Several in vivo and in vitro studies have demonstrated that GH is important in the regulation of both bone formation and bone resorption. In Figure 9 a simplified model for the cellular effects of GH in the regulation of bone remodeling is presented (Fig. 9). GH increases bone formation in two ways: via a direct interaction with GHRs on osteoblasts and via an induction of endocrine and autocrine/paracrine IGF-I. It is difficult to say how much of the GH effect is mediated by IGFs and how much is IGF-independent. GH treatment also results in increased bone resorption. It is still unknown whether osteoclasts express functional GHRs, but recent in vitro studies indicate that GH regulates osteoclast formation in bone marrow cultures. Possible modulations of the GH/IGF axis by glucocorticoids and estrogens are also included in Fig. 9. GH deficiency results in a decreased bone mass in both man and experimental animals. Long-term treatment (> 18 months) of GHD patients with GH results in an increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with a normal GH secretion. Recent clinical studies demonstrate that GH treatment of patients with normal GH secretion increases biochemical markers for both bone formation and bone resorption. Because of the short duration of GH treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. Interestingly, GH treatment to GHD adults initially results in increased bone resorption with an increased number of bone-remodeling units and more newly produced unmineralized bone, resulting in an apparent low or unchanged bone mass. However, GH treatment for more than 18 months gives increased bone formation and bone mineralization of newly produced bone and a concomitant increase in bone mass as determined with DEXA. Thus, the action of GH on bone metabolism in GHD adults is 2-fold: it stimulates both bone resorption and bone formation. We therefore propose "the biphasic model" of GH action in bone remodeling (Fig. 10). According to this model, GH initially increases bone resorption with a concomitant bone loss that is followed by a phase of increased bone formation. After the moment when bone formation is stimulated more than bone resorption (transition point), bone mass is increased. However, a net gain of bone mass caused by GH may take some time as the initial decrease in bone mass must first be replaced (Fig. 10). When all clinical studies of GH treatment of GHD adults are taken into account, it appears that the "transition point" occurs after approximately 6 months and that a net increase of bone mass will be seen after 12-18 months of GH treatment. It should be emphasized that the biphasic model of GH action in bone remodeling is based on findings in GHD adults. It remains to be clarified whether or not it is valid for subjects with normal GH secretion. A treatment intended to increase the effects of GH/IGF-I axis on bone metabolism might include: 1) GH, 2) IGF, 3) other hormones/factors increasing the local IGF-I production in bone, and 4) GH-releasing factors. Other hormones/growth factors increasing local IGF may be important but are not discussed in this article. IGF-I has been shown to increase bone mass in animal models and biochemical markers in humans. However, no effect on bone mass has yet been presented in humans. Because the financial cost for GH treatment is high it has been suggested that GH-releasing factors might be used to stimulate the GH/IGF-I axis. The advantage of GH-releasing factors over GH is that some of them can be administered orally and that they may induce a more physiological GH secretion. (ABSTRACT TRUNCATED)
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