PubMed Health⌕ Search

Biomedical subjects

C Farquharson

Publications and source records attributed to C Farquharson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Growth hormone and longitudinal bone growth in vivo: short-term effect of a growth hormone antiserum.

The control of longitudinal growth is poorly understood but GH is considered to be one of the major hormones regulating postnatal growth. However, there is dispute as to whether it has a direct or indirect action. To study the role of GH we used a polyclonal antiserum to rat GH and investigated changes in cell proliferation and enzyme activities associated with bone formation and resorption during longitudinal growth. IGF-I levels were measured by two independent RIAs, DNA synthesis by bromodeoxyuridine incorporation followed by immunocytochemistry and enzyme activities were quantified in situ by microdensitometry. After 1 day the percentage of chondrocytes undergoing DNA synthesis within the proliferative zone was reduced but no other parameters were affected. By day 4 the labelling index was the same as in pair-fed animals but the number of chondrocytes synthesising DNA was reduced as was the total width of the growth plate and that of the proliferative zone. Alkaline phosphatase (associated with mineralisation) was unchanged but glucose 6-phosphate dehydrogenase activity (associated with cell proliferation) was decreased. Osteoclastic tartrate-resistant acid phosphatase activity (associated with bone resorption) was also significantly reduced. Similar changes were apparent after 10 days. At no time was the circulating level of IGF-I decreased. These data suggest that, during longitudinal growth, GH affects the number of proliferating chondrocytes but not the percentage of cells undergoing DNA synthesis, indicating that its primary role may be on the commitment of prechondrocytes to a proliferative state. Furthermore, while GH does not seem to have any effect on skeletal mineralisation it may stimulate osteoclastic resorption of the primary spongiosa.

Acid Phosphatase↗
PubMed1994

Alterations in glycosaminoglycan concentration and sulfation during chondrocyte maturation.

We have used antibodies to chondroitin 4- and 6-sulfate and keratan sulfate along with Alcian blue staining of sulfated proteoglycans to investigate changes in content and sulfation within the avian growth plate. In normal chicks, chondroitin 4- and 6-sulfate content were similar in the proliferating and transitional zones but in the hypertrophic zone, chondroitin 4- and 6-sulfate were slightly lower (13% and 18%, respectively) and keratan sulfate was markedly lower (58%). Compared with the proliferative zone, Alcian blue staining of sulfated glycosaminoglycans was markedly lower in both the transitional (46%) and hypertrophic (22%) zones. In tibial dyschondroplasia, where chondrocyte maturation is arrested at the transitional zone, there was no difference in the chondroitin 4- and 6-sulfate or keratan sulfate staining between the proliferative and transitional zones, which were similar to normal birds. With Alcian blue staining there was no difference in the intensity of the staining within the proliferating zone compared with normal birds but staining in the transitional chondrocytes was markedly higher (39%). These results suggest that in the early steps of chondrocyte maturation there may be a decrease in the degree of glycosaminoglycan sulfation without any alteration in glycosaminoglycan concentration, and that further maturation may be accompanied by a change in the nature of the proteoglycans which may also affect the level of sulfation.

Alcian Blue↗
PubMed1993

In vivo effect of 1,25-dihydroxycholecalciferol on the proliferation and differentiation of avian chondrocytes.

A combination of immunocytochemistry and in situ biochemistry has been used to determine the in vivo effects of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] on the proliferation and differentiation of chondrocytes. Chicks were fed a diet supplemented with 1,25-(OH)2D3 (2.5, 5, or 10 micrograms/kg diet) for 3 weeks, and measurements were made in sections of growth plate of chondrocyte proliferation and rate of maturation through the growth plate [using bromodeoxyuridine (BrdUrd) labeling] and also chondrocyte differentiation [assessed by alkaline phosphatase (ALP) activity]. The labeling indices of the control and supplemented chicks were similar (23.1 +/- 1.3 versus 23.2 +/- 1.6%); however, within a 21 h period the BrdUrd-positive cells of the supplemented chicks had moved down the growth plate significantly farther than in the control chicks (71.0 +/- 2.8 versus 52.6 +/- 1.8%). Greater ALP (mean integrated absorbance) activity higher up the growth plate of the supplemented chicks indicated a more differentiated phenotype in cells closer to the epiphyseal junction. Within individual transitional chondrocytes ALP activity in the 10 micrograms/kg supplemented chicks was 26.6 +/- 0.85, which was significantly higher (p < 0.01) than that of the control chicks (19.2 +/- 0.9). These results suggest that 1,25-(OH)2D3 in vivo does not increase the rate of chondrocyte proliferation but accelerates the onset of maturation.

Alkaline Phosphatase↗
PubMed1993

Mitogenic action of insulin-like growth factor-I on human osteosarcoma MG-63 cells and rat osteoblasts maintained in situ: the role of glucose-6-phosphate dehydrogenase.

The mechanisms involved in the mitogenic actions of insulin-like growth factor-I (IGF-I) on skeletal cells are at present unclear. We have investigated the role of glucose-6-phosphate dehydrogenase (G6PD) in this mechanism and provide strong evidence that stimulation of G6PD activity is required for the growth promoting activities of IGF-I. IGF-I (10 ng/ml) significantly elevated G6PD activity in MG-63 human osteosarcoma cells within 30 min which preceded the IGF-I induced DNA synthesis in these cells. Inhibition of G6PD activity by epiandrosterone decreased DNA synthesis in IGF-I stimulated MG-63 cells but this was partly overcome by the addition of a combination of the four deoxyribonucleosides. IGF-I did not cause a general increase in cell metabolism as succinate dehydrogenase and iso-citrate dehydrogenase activity were not altered. Although IGF-I caused a significant increase in lactate dehydrogenase activity this was not inhibited by epiandrosterone. The culture of metatarsals of 4-week-old rats with IGF-I (10 ng/ml) also stimulated G6PD activity in osteoblasts lining the metaphyseal trabeculae.

Androsterone↗
PubMed1993

Studies on growth plate chondrocytes in situ: cell proliferation and differentiation.

In man, attaining full longitudinal growth and skeletal maturity may go towards preventing later problems, such as osteoporosis. In farmed species, it is becoming increasingly apparent that muscle growth or the calcium demands for reproduction have outstripped the ability of the skeleton to provide both support and sufficient calcium. Thus, understanding the mechanisms that control longitudinal growth is of vital importance. Methods for studying chondrocyte proliferation and differentiation increasingly rely on the use of isolated cells, but these do not reproduce in vivo conditions. It is therefore necessary to be able to assess chondrocyte function in situ in order to understand fully the actions of possible growth promoters and therapeutic agents. The control of chondrocyte proliferation seems to be heavily dependent on GH, which probably acts directly on the resting and proliferating chondrocytes (Fig. 3). In the former, it seems to regulate the commitment of prechondrocytes to the proliferative state, but the mechanisms whereby it achieves this are unclear. What is also unclear is the proportion of growth that is GH dependent and how much, if at all, the control of IGF-I production by nutritional and other factors contributes to longitudinal growth. The in situ biochemical approach has provided strong evidence that both TGF-beta and the c-myc proto-oncogene are involved in chondrocyte differentiation and may be early markers of this process (Fig. 3). Indirect evidence exists to support a role for c-myc expression in chondrocyte differentiation, as TGF-beta has been reported to have its mechanisms of action modulated by c-myc expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The control of chondrocyte differentiation during endochondral bone growth in vivo: changes in TGF-beta and the proto-oncogene c-myc.

The expression of transforming growth factor-beta and the c-myc proto-oncogene was studied in situ in the chondrocytes of the tibial growth plate of normal chicks and those with avian tibial dyschondroplasia in which the chondrocytes are developmentally arrested in the transitional phase between proliferation and differentiation. This results in an accumulation of unmineralised and avascular cartilage. Dyschondroplastic chicks showed reduced c-myc expression in the transitional chondrocytes but unaltered levels in the proliferating chondrocytes. Transforming growth factor-beta expression was reduced in the transitional chondrocytes of dyschondroplastic chicks. In areas where the lesion was being repaired there was evidence of increased expression of both c-myc protein and transforming growth factor-beta. Addition of 1,25-dihydroxyvitamin D to the diet, which is known to reduce the incidence of dyschondroplasia, resulted in an increase in c-myc production. These results suggest that both transforming growth factor-beta and the proto-oncogene c-myc may be important elements of the cascade of events that lead to chondrocyte differentiation, hypertrophy and mineralisation.

Alkaline Phosphatase↗
PubMed1992

The proto-oncogene c-myc is involved in cell differentiation as well as cell proliferation: studies on growth plate chondrocytes in situ.

A combination of immunocytochemistry and microdensitometry has been used to localize and quantify the expression of the proto-oncogene c-myc within chondrocytes of the proximal growth plates of rat and chick long bones. Although the c-myc protein was localized in all chondrocytes of the growth plate of both species the most intense staining was restricted to the proliferating and differentiating chondrocytes. These were identified by their ability to synthesize DNA (bromodeoxyuridine positive) and the presence of alkaline phosphatase activity, respectively. Species differences did exist with the c-myc concentration of the chick proliferating and differentiating chondrocytes being higher (128% and 240%, respectively) than the respective chondrocytes of the rat. The higher c-myc concentration in the chick proliferating chondrocytes paralleled the differences in the bromodeoxyuridine labelling index between the two species. In the rat, the concentration of c-myc protein present in the differentiating chondrocytes was 74% higher than in the respective proliferating chondrocytes, while in the chick it was 146% higher. The data not only provides further evidence for a role of the c-myc protein in cell proliferation but also suggests involvement of this protein in chondrocyte differentiation and/or hypertrophy.

Alkaline Phosphatase↗
PubMed1992

Cell proliferation and enzyme activities associated with the development of avian tibial dyschondroplasia: an in situ biochemical study.

Avian tibial dyschondroplasia is a disorder of endochondral ossification which results in the accumulation of noncalcified, avascular cartilage. We have investigated the changes in cell proliferation and enzyme activities within specific cell types in the growth plate of chickens with differing severity of the disease using in situ biochemical techniques that allow the quantification of enzyme activity in unfixed undecalcified sections of tissue. Lactate dehydrogenase activity in the prehypertrophic zone and tartrate-resistant acid phosphatase activity in osteoclasts/chondroclasts were not affected by the severity of the disease. Glucose 6-phosphate dehydrogenase activity in both the proliferating and prehypertrophic zones of the growth plate was reduced in chicks with both moderate and severe lesions. Cell proliferation within the proliferating chondrocytes was slightly reduced in the severely affected birds. Alkaline phosphatase activity in the prehypertrophic chondrocytes was markedly elevated in chicks with moderate and severe lesions. These results rule out an increased rate of chondrocyte proliferation as a possible mechanism for the development of tibial dyschondroplasia. The aetiology of the disease therefore appears to be related to the control of chondrocyte differentiation, mineralization, and vascularization by local and/or systemic growth factors.

Acid Phosphatase↗
PubMed1991

Immunolocalization of collagen types I, III and IV, elastin and fibronectin within the heart of normal and copper-deficient rats.

Collagen types I, III and IV, fibronectin and elastin were detected by immunohistochemistry in the normal and copper-deficient rat heart. All rats maintained on a copper-deficient diet for at least 6 weeks were found to have areas of abnormal distribution of these connective tissue components within the endo- and perimysium although the normal appearance observed in control animals prevailed. It appeared that the proliferation of the fibrillar collagens and fibronectin was associated with fibrosis and scar tissue formation. In contrast, the fragmented and disorganized appearance of the myocyte basement membrane and the endomysial elastin did not seem to be associated with the fibrotic process and may be an early indication of copper deficiency. The vascular system of the copper-deficient hearts appeared normal. These results are discussed with reference to the functional and mechanical abnormalities that occur in copper-deficient animals.

Animals↗
PubMed1990

Cell proliferation within the growth plate of long bones assessed by bromodeoxyuridine uptake and its relationship to glucose 6-phosphate dehydrogenase activity.

Bromodeoxyuridine (BrdUrd) was incorporated into the DNA of proliferating chondrocytes of the tibiae and metatarsal growth plate of rats of differing ages. Immunodetection of the incorporated BrdUrd was achieved using a monoclonal antibody to BrdUrd and indirect immunofluorescence procedures. The labelling index within the growth plate was found to decrease with advancing age in the tibia and metatarsal. Glucose 6-phosphate dehydrogenase (G6PD) activity appeared to be related to chondrocyte proliferation as a significant correlation was observed between G6PD activity and the labelling index of the tibial chondrocytes. The results of this study indicate that G6PD activity is a possible marker for cartilage growth and also that the BrdUrd technique has several advantages over the conventional autoradiographic methods for the assessment of cell replication.

Aging↗
PubMed1990

Endogenous mediators of growth.

In the present review it is not possible to discuss the effects of the numerous endogenous mediators of growth. What we have attempted to do is to indicate the areas of controversy and the need for further research. In our view, four main questions arise. First, what are the relative contributions of the direct and indirect effects of GH? Indeed, if GH can produce all its effects by local production of IGF, is the original somatomedin hypothesis still tenable? Second, how is the biological activity of the IGF modified by the presence of binding proteins? Because of the role of binding proteins in modulating IGF bioactivity, care must be taken when interpreting results from immunoassays for IGF because this will only represent the concentration of IGF not the level of biological activity, a situation which is analogous to that which pertains with certain polypeptide hormones (for review, see Robertson et al. 1987). Third, how are the activities of the osteoblast and osteoclast coupled so that in the mature adult, bone formation and bone resorption are roughly equivalent? Understanding of this process will undoubtedly involve the elucidation of the roles and interactions between a number of locally acting growth factors and systemic hormones and will lead to the understanding of certain metabolic bone diseases such as osteoporosis. Last, how is the response to local stimuli such as mechanical stress transduced? This is again probably dependent on the activity of local growth factors but may also involve changes in the interactions between bone cells and their underlying matrix components (Skerry et al. 1988).

Bone Development↗
PubMed1989

Immunolocalization of collagen types I and III in the arterial wall of the rat.

Collagen types I and III were located by immunofluorescence procedures in the aorta and coronary arteries of the rat. Type I collagen was most prevalent in the adventitia of the aorta with only small amounts present in the intima and media. Type III collagen appeared to be a significant component in the media of the aorta and also in the adventitia of both blood vessels. The intima and media of the coronary arteries did not stain strongly for either type I or III collagen. Neither staining procedure was altered with preincubation of the sections with hyaluronidase or chondroitinase ABC. These studies indicate that type III collagen is a major component of the adventitia which has previously not been recognized by immunohistochemical techniques, possibly due to masking of collagen staining with glycosaminoglycans.

Animals↗
PubMed1989

Excretion of pyridinium cross-links of collagen in ovariectomized rats as urinary markers for increased bone resorption.

Groups of 19-day-old rats were ovariectomized or were given sham operations. Measurements in urine of the pyridinium cross-links of collagen, pyridinoline and deoxypyridinoline, 7 weeks after surgery showed significantly higher amounts of cross-links relative to creatinine in the ovariectomized groups compared with the controls. Analyses before and after acid hydrolysis of the urine revealed that the increased excretion was only as free cross-link with no change in the concentrations of the bound forms. The loss of trabecular bone in the ovariectomized group was confirmed by immunocytochemical staining with antibodies to type I collagen. There were no differences between the ovariectomized and control groups in the concentrations of cross-links in the tibial bone or the articular cartilage. Measurements of free pyridinoline and deoxypyridinoline in urine therefore appear to provide a good index of the increased bone resorption induced by estrogen deficiency.

Amino Acids↗
PubMed1989

The effects of copper deficiency on the pyridinium crosslinks of mature collagen in the rat skeleton and cardiovascular system.

The 3-hydroxypyridinium crosslinks of collagen were quantified in tissues of the skeleton and cardiovascular system of normal and copper-deficient rats. The copper-deficient rats used in this study displayed retarded growth, cardiac hypertrophy, anemia, and lowered liver copper concentrations. Quantification of the crosslinks by high performance liquid chromatography indicated that there were lower concentrations of collagen crosslinks in the hearts of copper-deficient animals, a finding that was manifest in both right and left ventricles. This was in contrast to the collagen of the aorta where no alteration in crosslink concentration was observed. The femoral diaphysis of copper-deficient rats also had lower amounts of collagen crosslinks than copper-supplemented animals, whereas crosslinking in the tibial diaphysis and articular cartilage was relatively unaffected by copper deficiency. These results are discussed with reference to the cardiac and skeletal abnormalities that occur in copper-deficient animals.

Animals↗
PubMed1988

Immunohistochemical localization of native and denatured collagen types I and II in fetal and adult rat long bones.

Collagen turnover during rat long bone development and growth was investigated using immunofluorescence methods with specific polyclonal antibodies against native (triple helix) and denatured (breakdown products) forms of type I and II collagen. Labeling of cryostat sections with anti-native and denatured collagen type II antibodies resulted in a positive staining throughout the cartilage matrix of fetal and adult long bones. Likewise, native and denatured type I collagen could be detected in mineralized and non-mineralized bone matrix. Moreover, labeling with anti-denatured type I antibody evoked a strong intracellular staining of osteoblasts, but not of osteocytes. Denatured type I was also localized intra-pericellularly in the small chondrocytes comprising the primitive cartilage cores and the epiphyses of older long bones. On the other hand, apart from its localization in the cartilage matrix, denatured type II collagen was found specifically within the chondrocytes. These observations indicate that a continuous turnover of the major collagen types takes place in fetal and adult rat long bone tissue. Degradation of collagen apparently occurs intra- and extracellularly, and is mainly independent of the presence and activity of osteoclasts. The presence of denatured type I collagen in cartilage suggests that chondrocytes synthesize small amounts of type I collagen, which is immediately degraded to a denatured form.

Animals↗
PubMed1988

Female rats are susceptible to cardiac hypertrophy induced by copper deficiency: the lack of influence of estrogen and testosterone.

In contrast to a previous report (Fields M, Lewis C, Scholfield DJ, Powell AS, Rose AJ, Reiser S, Smith, JC. Proc Soc Exp Biol Med 183:145-149, 1986), female rats were shown to be susceptible to copper (Cu) deficiency giving rise to restriction of growth, cardiac hypertrophy, and anemia. The severity of these effects was, however, found to be less marked than in the male rats which had similar liver Cu levels. Castration or ovariectomy of Cu-deficient rats had little effect on CH or the other parameters associated with Cu deficiency, and supplementation of the neutered animals with estrogen or testosterone was similarly without effect. The ultrastructural appearance of the hypertrophied Cu-deficient female heart was similar to that previously found in males and was characterized by a large increase in mitochondrial area with disrupted cristae. The results also indicated that in contrast to Cu-deficient males iron (Fe) was not accumulated in the liver of the Cu-deficient female rats. It may be concluded that the limited protection of female rats to the effects of Cu deficiency observed in this study were unconnected with the sex steroids.

Animals↗
PubMed1988

The effects of reserpine upon the cardiac enlargement of copper deficiency.

Copper (Cu) deficiency, induced in rats by suckling from Cu-deficient dams and by offering a semisynthetic low-Cu diet from weaning, resulted in cardiac enlargement. This enlargement was not due to accumulation of excess fluid in the heart but was characterized by mitochondrial hypertrophy as demonstrated by electron microscopy and biochemical studies. Administration of reserpine limited the extent of cardiac enlargement; however, heart total noradrenaline (NA), unchanged by Cu deficiency, was significantly reduced by reserpine. It was concluded that cardiac enlargement in Cu deficiency was not directly related to NA concentration. An alteration in cardiac energy status, however, was suggested by reduction in activity of the nonheme iron-dependent enzyme, succinic dehydrogenase.

Age Factors↗