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Biomedical subjects

L G Raisz

Publications and source records attributed to L G Raisz.

At least 19 recordsLinked to original sources
PubMed1992

The interaction of heparin and basic fibroblast growth factor on collagen synthesis in 21-day fetal rat calvariae.

We examined the interactions of the glycosaminoglycan, heparin, and recombinant human basic fibroblast growth factor (bFGF) on collagen synthesis in 21-day fetal rat calvariae. In calvariae treated for 96 h, heparin (25 micrograms/ml) and bFGF (10(-9) M) inhibited collagenase-digestible protein (CDP) labeling by 52 and 60% of control, respectively, and the combination further inhibited CDP labeling. Inhibition of CDP labeling by heparin (25 micrograms/ml) or bFGF (10(-9), 10(-8) M) was similar in the presence or absence of aphidicolin (30 microM) an inhibitor of cell replication. Heparin selectively inhibited CDP labeling in the osteoblast rich central bone but bFGF alone or in combination with heparin inhibited CDP labeling both in the periosteum and central bone. Heparin and bFGF alone decreased steady state levels of alpha 1(I)procollagen messenger RNA (mRNA) at 24 h and the combination further decreased mRNA levels. A high concentration of insulin-like growth factor-1 (IGF-1, 3 x 10(-8) M) reversed the inhibitory effect of heparin on DNA synthesis and CDP labeling. In contrast, IGF-1 could not reverse the inhibitory effects of bFGF on CDP labeling but enhanced the stimulatory effects of bFGF on thymidine incorporation into DNA. We conclude that the inhibitory effects of heparin and bFGF on CDP are independent of effects on cell replication. We further conclude that both heparin and bFGF inhibit collagen synthesis at a pretranslational site since they decreased procollagen mRNA levels in osteoblasts. However, the inhibition of collagen synthesis by heparin and bFGF appears to involve divergent pathways since exogenous IGF-1 could overcome the effect of heparin but not bFGF on collagen synthesis.

Animals↗
PubMed1991

Effects of transforming growth factor-beta and IL-1 alpha on prostaglandin synthesis in serum-deprived osteoblastic cells.

We investigated the effects that the combination of IL-1 alpha and transforming growth factor-beta (TGF-beta) had on PGE2 production in a murine clonal osteoblastic cell line MC3T3-E1 and primary rat calvarial osteoblast-like cells. In serum-supplemented medium, IL-1 alpha was a potent stimulator of PGE2 production in MC3T3-E1 cells (50-fold increase with 0.1 ng/ml). TGF-beta (10 ng/ml) had only a small effect alone and no additional effect on IL-1 alpha-induced responses. In serum-deprived MC3T3-E1 cells, PGE2 responses to IL-1 alpha were either absent or markedly reduced. TGF-beta alone had small effects. However, simultaneous addition of TGF-beta with IL-1 alpha to MC3T3-E1 cells partially restored the ability of IL-1 alpha to generate a PGE2 response (10-fold increase in PGE2 with 0.1 ng/ml of both IL-1 alpha and TGF-beta). As with MC3T3-E1 cells, serum-deprived primary fetal rat calvarial osteoblastic cells also did not respond to IL-1 alpha, unless TGF-beta was present in the medium (sixfold increase in PGE2 with 0.1 ng/ml IL-1 alpha and 10 ng/ml TGF-beta). The synergistic effect of TGF-beta and IL-1 alpha was specific for PGE2 responses, because these factors did not synergistically affect cell proliferation, collagen and noncollagen protein synthesis, or alkaline phosphatase activity. The observed synergy was not associated with changes in the steady state cyclooxygenase (PGH synthase) mRNA levels. However, it did correlate with increased release of [3H]arachidonic acid from prelabeled serum-depleted MC3T3-E1 cells. Hence, the synergistic interactions of IL-1 alpha and TGF-beta on PGE2 appear to occur through an increase in the release of arachidonic acid substrate from phospholipid pools. These effects may be important for both normal bone turnover and the responses of bone to inflammatory and immune stimuli.

Alkaline Phosphatase↗
PubMed1991

The role of DNA synthesis in the responses of fetal rat calvariae to cortisol.

To determine the extent to which the effects of cortisol on collagen synthesis in 21 day fetal rat calvariae are linked to its effects on cell replication, calvariae were cultured for 24-72 h with 0.1 and 1 microM cortisol in the presence or absence of 1 mM hydroxyurea (HU) or 30 microM aphidicolin (APC), inhibitors of DNA synthesis. The incorporation of [3H]proline into collagenase-digestible protein (CDP) and [3H]thymidine into DNA were measured during the last 2 h of culture. At 24 h HU and APC decreased thymidine incorporation by greater than 90%, and this remained low for the duration of culture. In contrast, cortisol reduced thymidine incorporation by only 44% at 72 h. Although cortisol caused a 24 h stimulatory effect and a 48 and 72 h inhibitory effect on CDP labeling and the percentage of collagen being synthesized (PCS), HU, and APC had no effect on basal CDP labeling or PCS over the 72 h culture period. Cortisol caused parallel alterations in the steady-state levels of alpha-1(I) procollagen mRNA, suggesting that its effects occur at the pretranslational level. At 24 h HU and APC did not prevent the stimulatory effect of cortisol on CDP labeling and PCS. At 48 h the inhibitory effects of cortisol on CDP labeling and PCS were observed in the presence of APC but not in the presence of HU. At 72 h the inhibitory effects of cortisol on CDP labeling and PCS were still observed in the presence of HU and APC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effects of potassium peroxydiphosphate on bone resorption.

Potassium peroxydiphosphate (KPDP) is a slowly hydrolyzed pyrophosphate analog that can release hydrogen peroxide during hydrolysis. We tested its effects on the resorption of cultured fetal rat long bones as measured by the release of previously incorporated 45Ca, both by direct addition of KPDP to the medium and after preincubation of KPDP with large-molecular-weight resorbing factors followed by dialysis to reduce the KPDP concentration. With direct addition, KPDP at a concentration of 1 mM could inhibit the resortive response to bacterial lipopolysaccharide (LPS), parathyroid hormone (PTH), prostaglandin E2 (PGE2), and mouse recombinant interleukin-1 (mrIL-1). The response to LPS was partially inhibited at 0.3 mM KPDP. Control resorption in the absence of stimulators was also inhibited. Potassium pyrophosphate at 1 mM was less effective as an inhibitor of bone resorption. The inhibitory effects of KPDP did not appear to be due entirely to nonspecific toxicity since partial recovery occurred after it was removed. There was no significant decrease in [3H]thymidine or [3H]proline incorporation into bones incubated with KPDP at 1 mM for 5 days, but [3H]proline incorporation was decreased at 24 h, suggesting that KPDP may have a general inhibitory effect on bone cells. When media with and without stimulators of resorption were incubated overnight at 4 degrees C with KPDP at 5.8 mM and then dialyzed to bring the concentration to below 0.3 mM, the bone-resorbing activity of PTH, LPS, and mrIL-1 was completely lost. This may have been due to the slow release of hydrogen peroxide; however, preincubation with equimolar concentrations of H2O3 caused only partial inactivation of PTH and LPS. LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effects of acid and basic fibroblast growth factor and heparin on resorption of cultured fetal rat long bones.

We tested acid and basic fibroblast growth factor (aFGF and bFGF), members of the heparin binding FGF family, for their ability to stimulate bone resorption as measured by the release of previously incorporated 45Ca from cultured fetal rat long bones in the presence and absence of heparin. Purified low-molecular-weight heparin (LMW heparin) at 5-125 micrograms/ml had no direct stimulatory effect. There was little effect from aFGF (10(-11)-10(-8) M) alone, but increased resorption was observed in the presence of LMW heparin. With bFGF, increased bone resorption was observed at 10(-9) M but not at 10(-8) M. The stimulatory effects of aFGF and bFGF in the presence of LMW heparin were not blocked by the addition of indomethacin (10(-6) M), which blocks prostaglandin production, or hydroxyurea (10(-3) M), which blocks DNA synthesis. However, pretreatment with aphidicolin (3 x 10(-5) M), a potent inhibitor of DNA synthesis, blocked the effect of acid FGF and diminished the effect of bFGF. These results indicate that both aFGF and bFGF can stimulate bone resorption by a prostaglandin-independent mechanism, particularly in the presence of heparin. The activation of FGF-mediated bone resorption by heparin could play a role in producing the osteoporosis that has been described with heparin therapy and mastocytosis.

Animals↗
PubMed1991

Effect of 1,25-dihydroxyvitamin D3 on prostaglandin E2 production in cultured mouse parietal bones.

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] was tested for its effects on prostaglandin E2 (PGE2) production and bone resorption in cultured mouse parietal bones. We found that at 24 h 1,25-(OH)2D3 increased 45Ca release but did not affect PGE2 production. However, at 48 h 1,25-(OH)2D3 produced a dose-related increase in PGE2 production. PGE2 production was increased with 1,25-(OH)2D3 at 10(-10)-10(-8) M, and 45Ca release was increased with 1,25-(OH)2D3 at 10(-11)-10(-8) M. The effects of 1,25-(OH)2D3 on PGE2 production persisted in the presence of cortisol (10(-8) M), and the effects were greater in the presence of arachidonic acid (10(-5) M) or fetal bovine serum (10%). Human interleukin-1 alpha (IL-1, 1 ng/ml) and bovine parathyroid hormone-(1-34) (PTH, 10 ng/ml) increased PGE2 production earlier and to a greater extent than 1,25-(OH)2D3. The PGE2 response to IL-1 and PTH was not affected by 1,25-(OH)2D3 at 24 h, but at 48 h 1,25-(OH)2D3 (10(-8) M) increased the PGE2 response to both IL-1 and PTH. The stimulation of 45Ca release at 48 h by high concentrations of 1,25-(OH)2D3, PTH, or IL-1 was similar, and there was no evidence for an additive effect. To test for an effect of 1,25-(OH)2D3 on endogenous IL-1 production, experiments were performed in the presence of an IL-1 receptor antagonist (IL-1Ra, 1000 ng/ml), which has been found to block selectively IL-1 effects on bone resorption and PG production.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Mechanism of regulation of prostaglandin production by parathyroid hormone, interleukin-1, and cortisol in cultured mouse parietal bones.

Bovine PTH-(1-34) (PTH), human recombinant interleukin-1 alpha (IL-1), and cortisol were tested for their effects on bone resorption, prostaglandin (PG) production, and PG endoperoxide synthase (PGH synthase or cyclooxygenase) mRNA levels in cultured mouse parietal bones. Cultures were treated with PTH and IL-1 in the presence and absence of cortisol and arachidonic acid (AA). We found that both PTH and IL-1 stimulated the release of PGE2 and 6-keto-PGF1 alpha (the stable metabolite of PGI2). Stimulation of each metabolite by IL-1 at 0.6-60 pM was 2- to 118-fold, and that by PTH at 24 pM to 24 nM was 3- to 53-fold. Thus, IL-1 was 40-fold more potent than PTH in stimulating PG release. Moreover, IL-1 showed 2- to 3-fold greater efficacy than PTH in stimulating PGE2 release. However, IL-1 was only 4-fold more potent and no more effective than PTH in stimulating 45Ca release. IL-1 (60 pM) and PTH (2.4 nM) stimulation of PGE2 production showed a similar time course, with a lag phase of 0.75-1.5 h. Cortisol (1-100 nM) reduced basal PGE2 production and calcium release. The absolute amounts of PG produced in response to PTH and IL-1 were reduced in the presence of cortisol, but in the presence of AA the relative increases were still from 2.5- to 26-fold compared with levels in cultures treated with cortisol alone. Cortisol reduced the stimulation of 45Ca release by IL-1, but not by PTH. AA (10(-5) M) amplified PG production in response to PTH and IL-1, but not 45Ca release. In bones labeled with [3H]AA, IL-1 and PTH increased [3H]PGE2 and [3H]6-keto-PGF1 alpha release, as measured by HPLC and TLC. IL-1 slightly increased [3H]AA release, but PTH did not. Cortisol decreased [3H]AA release. To test for an effect on PG production at the level of PGH synthase, mRNA levels were measured. mRNA was increased by both PTH and IL-1 to a similar extent despite the greater effect of IL-1 on PGE2 production. Cortisol did not change PGH synthase mRNA levels and did not block the stimulation by PTH or IL-1. We conclude that IL-1 is a more potent stimulator of PG production and bone resorption than PTH. Stimulation of PG production by both PTH and IL-1 is mediated at least in part by increasing PGH synthase, but IL-1 may have an additional effect on AA release.

Animals↗
PubMed1991

Prostaglandin E2 stimulates insulin-like growth factor I synthesis in osteoblast-enriched cultures from fetal rat bone.

Prostaglandin E2 (PGE2) affects both bone resorption and formation, but its mechanism of action remains unclear. PGE2 is known to elevate intracellular cAMP levels in a variety of culture systems. Agents that increase cAMP in primary osteoblast-enriched (Ob) cultures enhance the synthesis of skeletal insulin-like growth factor I (IGF-I), a potent anabolic factor for bone. A 5 min exposure to PGE2 at 0.01-1 microM enhanced cAMP synthesis in Ob cultures by 8- to 54-fold, and within 6 h produced up to a 3- fold increase in steady state prepro-IGF-I transcripts. The stimulatory effect of PGE2 on IGF-I messenger RNA was first evident within 4 h of treatment and remained elevated for at least 24 h. Furthermore, 0.01-1 microM PGE2 increased immunoreactive IGF-I polypeptide accumulation by 1.9- to 4.7-fold. In contrast PGE2 did not elevate steady state IGF-II mRNA or polypeptide levels within this time frame. Although PTH increase cAMP, intracellular calcium, and PGE2 production by bone cells, our previous studies indicate that the stimulatory effect of PTH on IGF-I production is cAMP, but not calcium dependent. Inhibition of PGE2 synthesis by exposure to indomethacin did not alter basal or PTH-stimulated IGF-I levels, substantiating that the effect of PTH on IGF-I is not PGE2 dependent. These studies indicate that PGE2 production, a feature common to many agents that enhance bone resorption, could contribute to the coupling of bone resorption and new bone formation, by way of its ability to increase cAMP and, consequently, IGF-I synthesis by the osteoblast.

Animals↗
PubMed1991

Cortisol modulates the actions of interleukin-1 alpha on bone formation, resorption, and prostaglandin production in cultured mouse parietal bones.

Previous studies have shown that both interleukin-1 (IL-1) and glucocorticoids inhibit collagen synthesis in bone organ and cell cultures. In this study we examined their interactions in cultured neonatal mouse parietal bones. IL-1 alpha stimulated [3H]thymidine incorporation. Cortisol decreased thymidine incorporation, but did not block the effect of IL-1. Both cortisol and IL-1 alpha decreased the incorporation of [3H]proline into collagenase-digestible protein (CDP) and reduced alpha 1(I)procollagen mRNA levels at 72 h. Noncollagen protein (NCP) labeling was increased by IL-1 and decreased by cortisol. In the presence of cortisol, IL-1 alpha (6 pM) increased CDP as well as NCP labeling. The increase in CDP labeling was paralleled by an increase in alpha 1(I)procollagen mRNA, suggesting a pretranslational site for the cortisol-IL-1 alpha interaction. In the same bones, cortisol consistently blocked IL-1 alpha-stimulated 45Ca release and prostaglandin E2 (PGE2) production. The ability of IL-1 alpha to increase CDP in the presence of cortisol was the same in the presence or absence of indomethacin, an inhibitor of PGE2 synthesis, or aphidicholin (30 microM), an inhibitor of DNA synthesis, indicating that the reversal was neither PG mediated nor dependent on cell proliferation. In conclusion, our results demonstrate that IL-1 inhibits collagen, but not NCP or DNA, synthesis and that cortisol inhibits IL-1 alpha-induced bone resorption and PGE2 production and reverses its inhibitory effect on collagen synthesis in cultured neonatal mouse calvariae.

Animals↗
PubMed1990

Natural and recombinant human IL-1 receptor antagonists block the effects of IL-1 on bone resorption and prostaglandin production.

Inhibitory factors towards IL-1 have been identified in the urine and in the supernatants of human monocyte cultures and have been shown to act as receptor antagonists. We have investigated whether a natural inhibitor purified from human urine (uIL-1ra) and a recombinant molecule expressed using the gene for an IL-1 antagonist isolated from monocytes (rIL-1ra) can alter responses to human rIL-1 alpha in organ cultures of fetal rat long bones and neonatal mouse calvariae. The two preparations probably contained similar or identical molecules, because an antibody to rIL-1ra reacted with uIL-1ra by Western blot analysis. uIL-1ra and rIL-1ra specifically blocked stimulation of bone resorption by rIL-1 in both culture systems, as well as the increase in PGE2 production in cultured calvariae. Resorptive effects of parathyroid hormone and TNF-alpha were not blocked. The uIL-1ra preparation had some intrinsic resorbing activity, but on gel chromatography this appeared in fractions that eluted earlier than uIL-1ra. Concentration ratios of rIL-1ra to rIL-1 as low as 10 could block the resorptive response of fetal rat long bones, whereas concentration ratios of 100 to 1000 were required to block IL-1 action on neonatal mouse calvariae. The inhibitory effects appeared to be competitive, because increasing concentrations of IL-1 overcame the block of bone resorption in both systems and the inhibition of PGE2 production in calvariae.

Animals↗
PubMed1990

Glucocorticoid-induced osteoporosis: pathogenesis and management.

PURPOSE: To review the clinical picture, pathogenesis, and management of glucocorticoid-induced osteoporosis. DATA IDENTIFICATION: Studies published since 1970 were identified from a MEDLINE search, articles accumulated by the authors, and through bibliographies of identified articles. STUDY SELECTION: Information for review was taken from 160 of the more than 200 articles examined. DATA EXTRACTION: Pertinent studies were selected; the relative strengths and weaknesses of these studies are discussed. RESULTS OF DATA SYNTHESIS: Studies in tissue and organ cultures suggest that glucocorticoids have a direct effect on bone, causing inhibition of bone formation and enhancing bone resorption. Glucocorticoids decrease calcium absorption from the intestine and increase renal excretion. Osteoporosis occurs in at least 50% of persons who require long-term glucocorticoid therapy. Long-term trials of therapy for the prevention of glucocorticoid-induced osteoporosis have not been done, but reasonable recommendations include the use of a glucocorticoid with a short half-life in the lowest dose possible, maintenance of physical activity, adequate calcium and vitamin D intake, sodium restriction and use of thiazide diuretics, and gonadal hormone replacement. In refractory cases, the use of calcitonin, bisphosphonates, sodium fluoride, or anabolic steroids should be considered. CONCLUSIONS: Osteoporosis is common in patients requiring long-term treatment with glucocorticoids. Careful attention to preventive management may minimize the severity of this serious complication.

Animals↗
PubMed1990

Structural determinants of the capacity of heparin to inhibit collagen synthesis in 21-day fetal rat calvariae.

Earlier work from our laboratory demonstrated that heparin inhibits type I collagen and DNA synthesis in fetal rat calvariae in vitro. In this paper we have analyzed the structural features of heparin that determine its inhibitory effect on collagen synthesis. These experiments were performed using unmodified heparins and low-molecular-weight heparins from different manufacturers, nonheparin glycosaminoglycans, desulfated heparins, anticoagulant and nonanticoagulant heparin, and chemically defined heparin oligosaccharides. Low-molecular-weight heparin (Mr 3700-5100) inhibited collagen synthesis, but oligosaccharides (disaccharides to decasaccharide, Mr 665-3000) did not. The glycosaminoglycans chondroitin sulfate B, heparan sulfate, and hyaluronic acid did not alter collagen synthesis but dextran sulfate was as inhibitory as unmodified heparin. Nonanticoagulant as well as anticoagulant low-molecular-weight heparin fractions inhibited collagen synthesis. Modification of heparin by total desulfation, O-desulfation, or N-desulfation and re-N-acetylation resulted in the loss of inhibitory property, suggesting that the degree of sulfation contributed to heparin's inhibitory effect. Low-molecular-weight heparins from different manufacturers were just as inhibitory as native heparin on collagen synthesis. We therefore conclude that low-molecular-weight heparin compounds offer no protection against heparin-induced osteoporosis. Our findings also suggest that the size and sulfation of a heparin-derived oligosaccharide contribute to its ability to inhibit collagen synthesis in bone.

Animals↗
PubMed1990

Effects of androgens on parathyroid hormone and interleukin-1-stimulated prostaglandin production in cultured neonatal mouse calvariae.

In this study we show direct inhibitory effects on prostaglandin E2 (PGE2) production by the androgens, testosterone (T) and dihydrotestosterone (DHT), in cultured neonatal mouse calvariae. After 24 h of preculture with or without androgens, bones were treated with bovine (1-34)-parathyroid hormone (PTH) or recombinant human interleukin-1 alpha (IL-1). During preculture androgens decreased PGE2 release only in those experiments in which control PGE2 was high. PTH increased medium PGE2 9-fold at 24 h, and 10(-11) M T inhibited this increase by 50%. Treatment with IL-1 for 24 h increased medium PGE2 19- to 22-fold, and 10(-10) M T and DHT inhibited this increase by 60 and 70%, respectively. T did not significantly affect the PTH-stimulated release of previously incorporated 45Ca or alter the PTH inhibition of incorporation of [3H]proline into collagenase-digestible protein. IL-1 stimulated 45Ca release by 60-80%, and small but significant reductions of 20-30% were seen with T and DHT. This study shows that T and DHT have direct effects on bone at physiologic concentrations, similar to our previous study in which PTH-stimulated PGE2 production in the same culture system was inhibited by physiologic concentrations of 17 beta-estradiol, and suggests that prostaglandins may mediate some of the effects of androgens in vivo.

Androgens↗
PubMed1990

Glucocorticoids stimulate resorption in fetal rat parietal bones in vitro.

The effect of glucocorticoids on bone resorption was examined in a serum-free mineralizing organ culture system derived from 20 day fetal rat parietal bones. Bone resorption was assessed by prelabeling the fetal rats in utero with 45Ca and determining the daily release of 45Ca into the medium of cultured bones. During the first 24 h of treatment a transient stimulation of bone resorption was found; 4.5 +/- 0.3% of the total 45Ca was released into the medium with 1 nM corticosterone and 4.1 +/- 0.2% with 10 nM corticosterone compared to 2.9 +/- 0.2% in control bones. Treatment with 1 and 10 nM dexamethasone for 24 h also showed an increase in 45Ca release compared to control bones. During the same time period 45Ca release was 6.9 +/- 1.4% with 10 nM parathyroid hormone. At later time points 100 and 1000 nM corticosterone inhibited 45Ca release, but 1 and 10 nM corticosterone values were similar to controls. At 24 h the number of osteoclasts per mm2 tissue in bone lacunae was significantly elevated with 1-100 nM corticosterone and 10 nM parathyroid hormone compared to control bones. In control bones 0.10 +/- 0.05 osteoclasts per mm2 of tissue were found, but 0.59 +/- 0.21 osteoclasts per mm2 were seen with 10 nM corticosterone and 1.50 +/- 0.34 with 10 nM parathyroid hormone. An additional assay of bone resorption, the release of lysosomal beta-glucuronidase into the medium was also elevated in glucocorticoid and parathyroid hormone-treated cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Comparison of the effects of amino-terminal synthetic parathyroid hormone-related peptide (PTHrP) of malignancy and parathyroid hormone on resorption of cultured fetal rat long bones.

We have compared the effects of of various synthetic amino-terminal forms of human parathyroid hormone-related peptide (PTHrP) of malignancy with synthetic parathyroid hormone (PTH) on the resorptive responses of fetal rat long bones in organ culture. PTH and PTHrP increased 45Ca release at concentrations of 0.1-25 nM. PTHrP (1-40) and bovine PTH (1-34) were more potent than human PTH (1-34) and PTHrP (1-34). However, the slopes of the dose-response curves and the maximal resorptive effects were similar. There was a marked decrease in the potency of amino-terminal PTHrP peptides as the length was decreased. PTHrP (1-29) and PTHrP (1-25) were inactive at 120 nM. Further comparison of bPTH (1-34) and PTHrP (1-34) showed that both could induce bone resorption after a brief (6 hours) exposure and that the response to PTHrP (1-34) was qualitatively similar to that of bPTH (1-34) with respect to enhancement by ACTH and inhibition by calcitonin and glucocorticoids. Hydroxyurea and indomethacin did not block the resorptive response to either agonist. Cyclic AMP production in response to PTHrP (1-34) and (1-40) was similar to that for bPTH (1-34) in ROS 17/2.8 cells. The cyclic AMP (cAMP) response was much smaller in fetal rat long bones and calvariae, and bPTH was more potent than PTHrP. These studies confirm that PTHrP is quantitatively similar in its effects on bone resorption to PTH and are consistent with the two agents acting on the same receptor.

Animals↗
PubMed1990

Effect of heparin on bone formation in cultured fetal rat calvaria.

To assess the effects of heparin on bone formation we measured [3H]proline incorporation into collagenase-digestible (CDP) and noncollagen protein (NCP), [3H]thymidine (TdR) incorporation into DNA, and DNA content in 21-day-old fetal rat calvaria cultured in BGJ medium with bovine serum albumin for 24-96 hours. Heparin at 5-125 micrograms/ml decreased TdR incorporation by 26-51% at 24 and 96 hours. At 96 hours, heparin 5, 25, and 125 micrograms/ml decreased [3H]proline incorporation into CDP by 41, 48, and 32%, respectively, with no significant change in NCP. To evaluate the possible role of PGE2 in these inhibitory responses, media PGE2 concentration was measured and the effects of heparin on CDP labeling and DNA synthesis were tested in the presence of indomethacin, piroxicam, and flurbiprofen to inhibit endogenous prostaglandin E2 (PGE2) production and in the presence of a high concentration (10(-7) M) of exogenous PGE2. Heparin did not alter PGE2 production at 24 hours but at 48 hours there was a significant reduction. At 96 hours, indomethacin (10(-6) M) inhibited [3H]-proline incorporation into CDP by 38% but had no effect on the labeling of NCP. Heparin had no further significant inhibitory effect in the presence of indomethacin. Piroxicam and flurbiprofen did not alter DNA content and had a smaller inhibitory effect than indomethacin on the labeling of CDP. Moreover, addition of heparin produced a further inhibition of CDP and DNA content and finally, heparin decreased CDP labeling by 71% in the presence of PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effects of vitamin D-binding protein on bone resorption stimulated by 1,25 dihydroxyvitamin D3.

Vitamin D and its metabolites are tightly bound to the serum vitamin D-binding protein (DBP) and only the free hormone is considered to be physiologically active. On the other hand, DBP could interact with cell membranes and even favor its intracellular entry. The present study was undertaken to examine the effects of DBP on bone resorption stimulated by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Forelimb bones from 19-day-old fetal rats were cultured for 5 days in the presence of purified human or rat serum albumin (hSAP or rSAP) and 1,25(OH)2D3, with or without human or rat DBP (hDBP or rDBP). Bone resorption was assessed by measuring the release of previously incorporated 45Ca. We found that the resorptive response to 1,25(OH)2D3 was minimally altered by hDBP (5 microM). The minimal effects of hDBP on 1,25(OH)2D3 activity on rat bones might be explained by a 6-fold lower affinity of hDBP (1.1 x 10(7) M-1) than rDBP (5.9 x 10(7) M-1) for 1,25(OH)2D3 or by species differences in cellular recognition of DBP. In a homologous rat system, however, rDBP at low (0.5 microM) or physiological (5 microM) concentration significantly decreased 1,25(OH)2D3-induced bone resorption. These data therefore support the hypothesis that free rather than DBP-bound 1,25(OH)2D3 is physiologically important.

Animals↗