ISSN:0884-0431    

DOI:10.1002/jbmr.5650050602

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractThe structure of a novel protein, parathyroid hormone‐related protein (PTHrP), secreted by human tumors associated with hypercalcemia has recently been determined. Administration of a synthetic fragment of this protein in vivo reproduces features of the clinical paraneoplastic syndrome of humoral hypercalcemia of malignancy and produces biologic responses closely similar to those obtained with parathyroid hormone (PTH). A PTH antagonist designed to reversibly occupy PTH receptors inhibited major actions of the tumor peptide in vivo, including phosphaturia, urinary cAMP excretion, and increased serum ionized calcium. These studies indicate that PTHrP and PTH mediate their bioactivities through shared receptors in vivo and establish a potential specific mechanism‐based approach utilizing PTH antagonists for the therapy of tumor‐associated hypercal

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050603

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractAmmonium chloride (NH4CI) is used as a urinary acidifier in the treatment and prevention of feline urologic syndrome. It is reported to cause alterations in calcium and bone metabolism in humans, dogs, and rats. Adult cats with normal renal function were fed 1.5% NH4CI for 6 months to study the effects of chronic dietary acidification on trabecular bone remodeling of the iliac crest and bone mineral density (BMD) of lumbar vertebral trabecular bone and femoral cortex. Histomorphometric analyses of iliac crest biopsies were performed before and after treatment. Static and dynamic parameters of bone resorption and formation were determined. Single‐energy quantitative computed tomography (SEQCT) was used to measure lumbar trabecular and femoral cortical BMD. There were no significant treatment effects in iliac crest trabecular bone remodeling or BMD of the vertebrae and femora. Bone remodeling activity decreased with time in both acidotic and control cats. Vertebral BMD increased with time in both groups of cats, whereas no change was seen in the femora. Thus, chronic dietary acidification for 6 months with therapeutic levels of NH4CI produced no significant changes in trabecular bone remodeling or bone mineral density in adult cat

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050604

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractThe plasma membrane fraction of chicken osteoclasts was purified utilizing 20% continuous Percoll gradients. Biochemical marker enzyme analysis (ouabain‐sensitive Na+, K+‐ATPase and 5′‐nucleotidase) indicated that plasma membrane enrichment was 11.87‐fold and 7.25‐fold, respectively, and contamination with mitochondria, endoplasmic reticulum, and lysosomes was low as determined by succinic dehydrogenase, NADH dehydrogenase, andN‐acetylglucosaminidase activities, respectively. SDS latency of Na+K+‐ATPase and 5′‐nucleotidase activities of the isolated plasma membranes revealed that 43‐50% of vesicles were sealed, with 10‐16% in the inside‐out orientation, depending on the membrane fraction used. Electron microscopy confirmed the vesicular nature of the plasma membrane fraction. The plasma membrane Ca2+‐ATPase had a high‐affinity(KCa= 0.22 μM;Kmax= 0.16 μmol/mg per min) and a low‐affinity (KCa= 148 μM; Vmax= 0.37 μtmol/mg per min) component. Calmodulin (0.12 μM) had no effect on Ca2+‐ATPase activity. However, trifluoperazine (0.1 mM), a calmodulin antagonist, strongly inhibited especially the high‐affinity component of the enzyme. Vanadate and lanthanum also caused inhibition. In the presence of CDTA, a potent Ca2+and Mg2+chelating agent, high‐affinity Ca2+‐ATPase activity was abolished, indicating that trace Mg2+was essential for activity. The Ca2+‐ATPase substrate curve using ATP showed a high‐affinity (Km= 12.3 μM;Kmax= 0.022 μmol/mg per min) and a low‐affinity (Km= 43.8 μM;Vmax= 0.278 μmol/mg per min) component. These results demonstrate that osteoclasts have a plasma membrane Ca2+‐ATPase with characteristics similar to the enzyme

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050605

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractA well‐characterized chicken osteoclast plasma membrane vesicle preparation manifested Mg2+‐dependent ATP hydrolyzing activity of 0.213 μmol inorganic phosphate released per mg protein per minute (n= 7). The Mg2+dependence showed a high‐affinity component with aKmgof 1.293 μM and Vmaxof 0.063 μmol Piper mg protein per minute, and a low‐affinity component with a KMgof 297.6 μM and aVmaxof 0.232 μmol Piper mg protein per minute. The Mg2+‐ATPase activity was inhibited by N, N1‐dicyclohexylcarbodiimide (DCCD, 0.2 mM, 50.7%),N‐ethylmaleimide (0.5 mM, 34.6%), nolinium bromide (1 mM, 29.9%), 4,4′‐di‐isothiocyano‐2,2′‐stilbene sulfonic acid (DIDS, 1 mM, 45.1%), andp‐chloromercuribenzoic acid (PCMB, 0.1 mM, 33.8%). Sodium orthovanadate (Na3VO4) at 1 μM had no effect but caused 29.5% inhibition at 1 mM. Na+could substitute for K+without loss of activity, NO3caused 19.5% inhibition when substituted for CI−, and acetate replacement of CI−resulted in 36.4% stimulation of Mg2+‐ATPase. ATP, GTP, ITP, CTP, and ADP were all hydrolyzed effectively.DCCD (0.2 mM), NEM (0.5 mM), nolinium bromide (1 mM), and DIDS (50 μM) almost completely abolished proton transport as measured spectrofluorometrically by acridine orange quenching. Na3VO4(1 mM) had no effect, and duramycin (80 μg/ml) inhibited transport 52.7%. K+replacement of Na+caused a 79.2% increase in initial proton transport rate. NO3‐ and acetate substitution of CI−resulted in a 46.1 and 55.7% decrease in transport, respectively. ATP supports transport far more effectively than the other nucleotides tested. ADP was ineffective. Experiments using the potassium ionophore, valinomycin, indicated that the proton pump functions electrogenically, with CI−most likely cotransported by an anion transporter. The proton pump also seems to have at least one anion‐sensitive site, elucidat

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050606

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractWe previously showed that the calcium channel blocker diltiazem raises cytosolic Ca2+and inhibits PTH release in bovine parathyroid cells. To investigate further possible mechanisms underlying these effects, we examined the effects of the more potent diltiazem analog TA‐3090, which is a Ca2+channel antagonist in vascular smooth muscle, on several aspects of the function of dispersed bovine parathyroid cells. Like diltiazem, TA‐3090 (10‐6‐10‐4) produced a dose‐dependent inhibition of immunoreactive PTH release at 0.5 mM Ca2+and raised the cytosolic Ca2+concentration by 25‐50% in fura‐2‐loaded parathyroid cells in the presence but not in the absence of extracellular Ca2, suggesting that it activated rather than inhibited Ca2+channels. To determine whether this compound affects other aspects of parathyroid function, we examined its effects on the inhibition of cAMP accumulation by Ca2+, a process we recently found to involve inhibition of cAMP generation by G1through a receptorlike mechanism, which is independent of changes in cytosolic Ca2+, TA‐3090 (10−4M) inhibited dopamine‐stimulated cAMP accumulation by up to 75% (from 663 to 166 fmol per 105cells), with a higher apparent potency at greater extracellular Ca2+concentrations. Moreover, the addition of 10−4M TA‐3090 potentiated the inhibitory effects of both Ca2+and Mg2+, decreasing the concentration of the divalent cation necessary to produce half‐maximal inhibition of cAMP accumulation by about twofold. In the absence of extracellular Ca2+, however, TA‐3090 had no effect on the stimulation of cAMP by dopamine or on the inhibition of dopamine‐stimulated cAMP accumulation by PGF2a, which also regulates cAMP via G1. Finally, the effects of TA‐3090 on the inhibition of cAMP by Ca2+were totally abolished following preincubation with pertussis toxin for 20‐24 h. These data suggest that TA‐3090 not only modulates the function of bovine parathyroid cells at the level of Ca2+channels per se but also may affect cAMP metabolism by potentiating the effects of high extracellular Ca2+concentrations at or near

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050607

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractIt is widely accepted that physical activity is beneficial to bone. However, the specific relationships of muscle strength to bone mineral density (BMD) are poorly understood. We examined strength and BMD in 59 women aged 18‐31 years who ranged in exercise patterns from sedentary to active. Mineral density of the right proximal femur (hip) and spine (L2‐4) was evaluated by dual‐energy x‐ray absorptiometry. BMD at the midradius was measured by single‐photon absorptiometry. Dynamic strength (one repetition maximum) was measured for the following muscle groups: back, elbow flexors (biceps), leg extensors (quadriceps), and the hip flexors, extensors, adductors, and abductors. Isometric grip strength was assessed by dynamometry.Mineral density at the hip correlated independently with muscle strength and body weight, but not with age. Specifically, femoral neck BMD was significantly correlated with back strength and weight, whereas trochanter and overall hip mineral density were significantly related to biceps, back, and hip adductor strength. Hip mineral density was not related to strength of the quadriceps group or to that of the hip flexors, extensors, or abductors. In addition, muscle strength was an independent predictor of lumbar spine and midradius mineral density. In stepwise multiple regression analysis, biceps strength proved the most robust predictor of hip BMD and grip strength best predicted bone density at the lumbar spine and radius.We conclude that muscle strength is an independent predictor of bone mineral density, accounting for 15‐20% of the total variance in bone density of young women. In addition, it appears that muscle groups with attachments that are distant from the spine and hip may exert an important influence on bone mineral density at

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050608

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractThe metabolism of 1,25‐dihydroxy vitamin D3[l,25‐(OH)2D3] by a human osteoblastic sarcoma cell line, U‐2 OS, and by primary cultures of human bone‐derived cells was examined at physiologic (5 x 10−11M) and pharmacologic (3.5 x 10−7M) substrate concentrations. For metabolite identification purposes, cells nearing confluency were incubated for 18 h with 3.5 x 10−7M l,25‐(OH)2D3in serum‐free medium. The putative vitamin D metabolites produced during this incubation were isolated from a total lipid extract of cells and medium. Identification of the metabolites was achieved by comigration with authentic standards on three high‐performance liquid chromatography systems, UV spectral analysis, mass spe trometry, and chemical modification by sodium borohydride and sodium metaperiodate. The identified metabolites produced from l,25‐(OH)2D3by the human osteosarcoma cells include 1,24,25‐trihydroxyvitamin D3; 24‐oxo‐l,25‐dihy‐droxyvitamin D3; 24‐oxo‐l,23,25‐trihydroxyvitamin D3; and 24,25,26,27‐tetranor‐l,23‐dihydroxyvitamin D3. Evidence is presented that (1) l,25‐(OH)2D3metabolism occurs constitutively in U‐2 OS osteosarcoma cells at a physiologic substrate concentration (5 x 11−11M), (2) the pathway can be further induced by pharmacologic 1,25‐(OH)2D3concentrations (10−7M), and (3) this pathway is present i

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050609

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of recombinant human growth hormone (rhGH) on biochemical markers of bone turnover and bone mineral content (BMC) were investigated in 20 normal male volunteers (aged 22‐31 years) randomized to treatment for 7 days with either rhGH (0.1 IU/kg subcutaneously twice a day) or placebo. Serum somatomedin C rose during treatment (p<0.001) but was not significantly different from baseline at day 14. The fasting urinary hydroxyproiine/creatinine (p<0.001) and calcium/creatinine ratios (p<0.01) increased during treatment and remained elevated for 4 and 2 weeks, respectively. Serum bone 7‐carboxyglutamic acid‐containing protein (BGP) increased during treatment (p<0.001) and remained elevated for 6 months (p<0.02). Serum bone alkaline phosphatase (B‐AP), after an initial fall in the treatment period (p<0.001), increased slightly in the following months (p<0.01). In the rhGH group BMC was significantly higher than the prestudy value at day 14 (p<0.05) but was unaltered at the end of study. The simultaneous increase in markers of bone resorption and formation during rhGH treatment followed by a decline in resorption parameters within a few weeks and the prolonged effect on BGP and B‐AP demonstrate that rhGH treatment stimulates osteoblasts and activates bone r

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050610

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY

摘要:

AbstractThere is increasing evidence that pamidronate and related compounds are effective in the prevention and treatment of osteoporosis. It is therefore of relevance to document the time course and mechanism of bis‐phosphonate action in this condition. To this end, the present study describes the biochemical responses to prophylactic treatment with oral pamidronate (APD, 150 mg/day) in 16 glucocorticoid‐treated patients and contrasts them with those in 19 steroid‐treated control subjects. Measurements were made over a period of 12 months.The treated patients showed a fall in urine hydroxyproline excretion at 6 weeks associated with a reduction in serum ionized calcium concentration, a rise in serum 1,25‐(OH)2D3, and a nonsignificant rise in serum bone gla protein (BGP). In contrast to BGP, serum alkaline phosphatase activity declined at 6 weeks, falling further at 3 months. Between 3 and 12 months, BGP levels paralleled those of alkaline phosphatase and hydroxyproline, all these being significantly below their initial values, and the other parameters returned to baseline. There was a gradual increase in plasma phosphate concentrations in the treated group over the 12 month period.It is concluded that pamidronate produces an acute and sustained inhibition of bone resorption followed by a more gradual reduction in bone formation. This transient dissociation results in a reduction in serum calcium, leading to a rise in serum 1,25‐(OH)2D3, which in turn stimulates BGP production. Thereafter, indices of bone turnover remain subnormal but serum calcium and 1,25‐(OH)2D3return

ISSN:0884-0431    

DOI:10.1002/jbmr.5650050611

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1990

数据来源: WILEY