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Michela Rossi, Giulia Battafarano, Viviana De Martino, Alfredo Scillitani, Salvatore Minisola, and Andrea Del Fattore

that cause excessive or impaired bone loss impact skeletal integrity as well as the immoderate, disorganised or reduced bone formation ( Del Fattore et al. 2012 ). Osteoblasts, the bone-making cells, derive from neural ectoderm to form craniofacial

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Kenneth A Philbrick, Carmen P Wong, Adam J Branscum, Russell T Turner, and Urszula T Iwaniec

and total bone mass ( Hamrick et al . 2004 , Ealey et al . 2006 , Gat-Yablonski & Phillip 2008 , Williams et al . 2011 ). At the cellular level, these abnormalities are associated with impaired endochondral ossification, lower bone formation due

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Koichiro Komatsu, Akemi Shimada, Tatsuya Shibata, Satoshi Wada, Hisashi Ideno, Kazuhisa Nakashima, Norio Amizuka, Masaki Noda, and Akira Nifuji

osteoblasts may be exerted through activation of ERKs ( Bellido & Plotkin 2011 ). Local application of N-BPs has been shown to promote bone formation around N-BP-coated implants in vivo ( Tanzer et al . 2005 , Gao et al . 2009 ). Previously, we reported

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Kotaro Azuma, Stephanie C Casey, Masako Ito, Tomohiko Urano, Kuniko Horie, Yasuyoshi Ouchi, Séverine Kirchner, Bruce Blumberg, and Satoshi Inoue

understand the roles of SXR/PXR in the bone tissue more precisely. Our results demonstrated that loss of SXR/PXR enhanced bone resorption and reduced bone formation in the trabecular bones and decreased thickness in the cortical bones. Moreover, these mice

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Lucie E Bourne, Caroline PD Wheeler-Jones, and Isabel R Orriss

physiological bone formation and pathological vascular calcification, and provides an overview of how these can be regulated by local and systemic factors. Bone formation Bone is a composite tissue comprised of both organic and mineral components

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J M Lean, J W M Chow, and T J Chambers

Abstract

We have recently found that administration of oestradiol-17β (OE2) to rats stimulates trabecular bone formation. It is not known, however, whether oestrogen has a similar action on bone formation rate under physiological circumstances. Oestrogen is known to suppress bone resorption, and oestrogen-deficient states in the rat, as in humans, are associated with an increase in bone resorption that entrains an increase in bone formation. To see if the latter masks a relative reduction in bone formation, due to oestrogen deficiency, we measured bone formation very early after ovariectomy, before the resorption-induced increase in bone formation becomes established. To do this, rats were administered fluorochrome labels before and after ovariectomy, spaced at weekly intervals in the first, and 3-day intervals in the second experiment.

In both experiments there was a decrease in indices of bone formation in the labelling interval immediately following ovariectomy such that, using the shorter fluorochrome intervals, the mineral apposition rate fell to 69%, the double-labelled surface to 45%, and the bone formation rate to 36% of sham-ovariectomized levels. The reduction was not sustained in the subsequent label intervals, presumably masked by the increase in bone formation attributable to increased resorption. These results suggest that if bone formation is assessed before this resorption-entrained increase in bone formation occurs, oestrogen deficiency is associated with a reduction in dynamic indices of bone formation. Thus, these experiments suggest that oestrogen stimulates bone formation under physiological circumstances, and that the osteopaenia that follows oestrogen deficiency may be attributable not only to an increase in bone resorption, but also to a relative deficiency in bone formation.

Journal of Endocrinology (1994) 142, 119–125

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Ghania Ramdani, Nadine Schall, Hema Kalyanaraman, Nisreen Wahwah, Sahar Moheize, Jenna J Lee, Robert L Sah, Alexander Pfeifer, Darren E Casteel, and Renate B Pilz

bone are cGMP independent ( van’t Hof & Ralston 2001 , Wimalawansa 2007 , Kalyanaraman et al. 2018 a ). To examine the role of PKG2 in post-natal bone acquisition, independently of its function in endochondral bone formation, we established

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J. H. Tobias and T. J. Chambers

ABSTRACT

While the osteopenia associated with oestrogen deficiency is thought to arise from a relative defect in bone formation with respect to resorption, oestrogen administration itself leads to a decrease, rather than an increase, in bone formation. This decrease in bone formation, which arises from oestrogen's inhibitory effect on bone turnover, presumably masks any underlying tendency of oestrogen treatment towards stimulation of bone formation. To investigate this further, we have examined the early effect of discontinuing the administration of oestradiol-17β (OE2; 40 μg/kg on bone formation indices in ovariectomized 13-week-old rats, before the turnover-induced increase in formation occurs. Histomorphometric indices were assessed at the proximal tibial metaphysis 0, 7, 10, 13 and 16 days following discontinuation of OE2 treatment. Measurements of body weight, uterine weight and longitudinal growth rate confirmed that there were rapid effects of OE2 deficiency on these parameters.

We could detect no significant increase in bone resorption, as measured by osteoclast surface and number, until 16 days after ending treatment with OE2; this was coincidental with a reduction in bone volume. Shorter periods of OE2 deficiency were associated with a marked decrease in bone formation, as assessed by dynamic histomorphometric indices. This inhibition of bone formation was largely due to a reduction in double fluorochrome-labelled trabecular surfaces, which were decreased by approximately 70%. We conclude that ending OE2 administration in ovariectomized rats caused a striking decrease in trabecular bone formation, if such indices are assessed prior to the subsequent turnover-induced increase in formation. This suggests that oestrogen treatment in ovariectomized rats is associated with a stimulatory effect on bone formation, in addition to its recognized anti-resorptive action.

Journal of Endocrinology (1993) 137, 497–503

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Therese Standal, Rachelle W Johnson, Narelle E McGregor, Ingrid J Poulton, Patricia W M Ho, T John Martin, and Natalie A Sims

for osteoporosis capable of inducing bone formation (reviewed in Hodsman et al . (2005) and Khosla et al . (2008) ). However, the mechanisms by which intermittent PTH increases bone mass remain unclear, and identifying downstream targets of this

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S Keila, A Kelner, and M Weinreb

Prostaglandin E(2) (PGE(2)) has been shown to exert a bone anabolic effect in young and adult rats. In this study we tested whether it possesses a similar effect on bone formation and bone mass in aging rats. Fifteen-month-old rats were injected daily with either PGE(2) at 5 mg/kg or vehicle for 14 days. PGE(2) treatment stimulated the rate of cancellous bone formation (a approximately 5.5-fold increase in bone formation rate), measured by the incorporation of calcein into bone-forming surfaces at the tibial proximal metaphysis. This effect resulted in increased cancellous bone area (+54%) at the same site. Since PGE(2) treatment resulted in a much higher proportion of bone surface undergoing bone formation and thus lined with osteoblasts, we tested the hypothesis that PGE(2) stimulates osteoblast differentiation from bone marrow precursor cells both in vivo and in vitro. We found that ex vivo cultures of bone marrow stromal cells from rats injected for 2 weeks with PGE(2) at 5 mg/kg per day yielded more ( approximately 4-fold) mineralized nodules and exhibited a greater (by 30-40%) alkaline phosphatase activity compared with cultures from vehicle-injected rats, attesting to a stimulation of osteoblastic differentiation by PGE(2). We also compared the osteogenic capacity of bone marrow from aging (15-month-old) versus young (5-week-old) rats and its regulation by PGE(2) in vitro. Bone marrow stromal cell cultures from aging rats exhibited a greatly diminished osteogenic capacity, reflected in reduced nodule formation ( approximately 6% of young animals) and lower alkaline phosphatase activity ( approximately 60% of young animals). However, these parameters could be stimulated in both groups of animals by incubation with 10-100 nM PGE(2). The magnitude of this stimulation was greater in cultures from aging rats (+550% vs +70% in nodule formation of aging compared with young rats). In conclusion, we demonstrate here that PGE(2) exerts a bone anabolic effect in aging rats, similar to the effect we and others have reported in young, growing rats. The PGE(2)-stimulated bone formation, which augments bone mass, most likely results from recruitment of osteoblasts from their bone marrow stromal precursors.