Loma Linda Veterans Association for Research and Education

Fluoride is one of the most potent but least well understood stimulators of bone formation in vivo. Bone formation was shown to arise from direct effects on bone cells. Treatment with sodium fluoride increased proliferation and alkaline phosphatase activity of bone cells in vitro and increased bone formation in embryonic calvaria at concentrations that stimulate bone formation in vivo.

To test the hypothesis that the reduction in gonadal function can lead to bone mass loss, a group of 12 men who had undergone bilateral orchidectomy at the age of 28.2 +/- 6.8 yr was evaluated. A progressive loss of the lumbar bone density was observed as a function of time after orchidectomy. Both the biochemical indices of bone resorption (urinary hydroxyproline/creatinine ratio and plasma tartrate-resistant acid phosphatase) and bone formation (serum osteocalcin and bone isoenzyme of alkaline phosphatase) were significantly increased in the patients compared with healthy controls. A positive correlation was found between urinary hydroxyproline excretion and percent change in spinal bone mineral density per yr. Because of this increase in the biochemically indicated bone resorption, nine of the patients were studied again after 1-3 yr and were thereafter treated with intranasal calcitonin. Urinary hydroxyproline excretion normalized after 3 months of treatment, and a significant decrease, but not to normal levels, was also observed in the mean values for the other biochemical indices of bone remodeling. Thus, testosterone deficiency, like estrogen deficiency, is associated with accelerated bone loss. The increase in osteoresorption was partially corrected by calcitonin treatment.

Previous studies have indicated that human immunodeficiency virus (HIV) is enclosed with a lipid envelope similar in composition to cell plasma membranes and to other viruses. Further, the fluidity, as measured by spin resonance spectroscopy, is low and the viral envelope is among the most highly ordered membranes analyzed. However, the relationship between viral envelope lipids and those of the host cell is not known. Here we demonstrate that the phospholipids within the envelopes of HIV-1RF and HIV-2-L are similar to each other but significantly different from their respective host cell surface membranes. Further, we demonstrate that the cholesterol-to-phospholipid molar ratio of the viral envelope is approximately 2.5 times that of the host cell surface membranes. Consistent with the elevated cholesterol-to-phospholipid molar ratio, the viral envelopes of HIV-1RF and HIV-2-L were shown to be 7.5% and 10.5% more ordered than the plasma membranes of their respective host cells. These data demonstrate that HIV-1 and HIV-2-L select specific lipid domains within the surface membrane of their host cells through which to emerge during viral maturation.

Eleven young adult subjects were briefly awakened after each minute of electroencephalographic-defined sleep for 2 consecutive nights after undisturbed laboratory adaptation and baseline nights. Two undisturbed recovery nights followed disruption nights. On disruption nights, subjects were awakened with an audiometer and signaled the awakening by subjective rating of sleep state or button push response. The disruption procedure resulted in severely fragmented sleep with only very small amounts of slow-wave and REM sleep. Total sleep time was reduced by approximately 1 h on each night. Arousal threshold increased 56 dB across the disruption nights. Following disruption, subjects performed more poorly and rated themselves sleepier than on baseline. The level of decline was similar to that seen after periods of total sleep loss of 40-64 h. Recovery sleep was also similar to that seen after total sleep loss. It was concluded that periodic disruption of sleep, perhaps by destroying sleep continuity, quickly results in impaired function. These data may help explain function loss in severe sleep apneics.

Bone volume is determined by the relative rates of bone formation and bone resorption. Recent research in several laboratories suggests that growth factors may act locally to modulate bone formation by stimulating osteoblast proliferation and activity. A number of bone-derived growth factors have been isolated and characterized from bone matrix extracts and from media conditioned by bone cells and bone organs in culture. The growth factors found in bone matrix include insulinlike growth factors I and II, transforming growth factor-β, acidic and basic fibroblast growth factor, plateletderived growth factor, and bone morphogenetic proteins. Conditioned medium from bone cells contains several of these growth factors and also hematopoietic factors. These bone matrix-derived growth factors have different biologic activities, including mitogenic, differentiating, chemotactic, and osteolytic activities. Evidence suggests that bone cells produce substantial quantities of growth factors for extracellular storage in bone matrix. Apart from being produced for extracellular storage, it is possible that growth factors secreted by bone cells have acute effects on their neighboring osteoblastic cells, i.e., paracrine action, or on themselves, i.e., autocrine action. The release of matrix-stored growth factors by bone resorption may mean that growth factors act as delayed paracrine agents, e.g., osteoblasts deposit growth factors in bone and later when these growth factors are released from bone via bone resorption, the growth factors stimulate osteoblast precursors to proliferate. The findings that bone is a storehouse for growth factors and that bone cells in culture produce and respond to bone growth factors suggest bone growth factors may act as potential determinants of local bone formation. This review is focused on the structure, regulation, and biologic actions of the known bone growth factors.

Prior studies have reported an association between the presence of the 7 repeat allele of the 48 bp repeat polymorphism of the third cytoplasmic loop of the dopamine D4 receptor gene (DRD4) and novelty seeking behaviors, attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), pathological gambling, and substance abuse. However, other studies have failed to replicate some of these observations. To determine whether we could replicate these associations we genotyped 737 individuals from four different groups of control subjects, and 707 index subjects from four different groups of impulsive, compulsive addictive behaviors including substance abuse, pathological gambling, TS, and ADHD. Chi-square analysis of those carrying the 7 allele versus non-7 allele carriers was not significant for any of the groups using a Bonferroni corrected alpha of.0125. However, chi-square analysis of those carrying any 5 to 8 allele versus noncarriers was significant for pathological gambling (p <.0001), ADHD (p </=.01) and the total index group (p </=.0004). When the comparison included all 7 alleles the results were significant for gamblers (p <.0001), TS (p </=.003), ADHD (p </=.003), and the total group (p </=.0002). There was a significant increase in the frequency of heterozygosity versus homozygosity for all alleles for pathological gamblers (p </=.0031) and the total index group (p </=.0015), suggesting that heterosis played a role. In the substance abuse subjects a quantitative summary variable for the severity of drug dependence, based on the Addiction Severity Index, showed that the scores varied by increasing severity across the following genotypes: 44 </= heterozygotes </= 77 </= 22. Studies of other quantitative traits indicated an important role for the 2 allele and the 22, 24, and 27 genotypes. All studies indicated that the role of the DRD4 gene in impulsive, compulsive, addictive behaviors is more complex than a sole focus on the 7 versus non-7 alleles.

Polymorphisms of three different dopaminergic genes, dopamine D2 receptor (DRD2), dopamine beta-hydroxylase (D beta H), and dopamine transporter (DAT1), were examined in Tourette syndrome (TS) probands, their relatives, and controls. Each gene individually showed a significant correlation with various behavioral variables in these subjects. The additive and substractive effects of the three genes were examined by genotyping all three genes in the same set of subjects. For 9 of 20 TS associated comorbid behaviors there was a significant linear association between the degree of loading for markers of three genes and the mean behavior scores. The behavior variables showing the significant associations were, in order attention deficit hyperactivity disorder (ADHD), stuttering oppositional defiant, tics, conduct, obsessive-compulsive, mania, alcohol abuse and general anxiety-behaviors that constitute the most overt clinical aspects of TS. For 16 of the 20 behavior scores there was a linear progressive decrease in the mean score with progressively lesser loading for the three gene markers. These results suggest that TS, ADHD, stuttering oppositional defiant and conduct disorder, and other behaviors associated with TS, are polygenic, due in part to these three dopaminergic genes, and that the genetics of other polygenic psychiatric disorders may be deciphered using this technique.

Human bone matrix is known to contain a battery of polypeptide growth factors. Since dentin is a mineralized tissue similar to bone in composition and perhaps in formation, human dentin was assayed for the presence of similar growth factors. Root dentin proteins were extracted by demineralization in 4 M guanidine hydrochloride (Gu) and 30 mM Tris (pH 7.4) containing 20% EDTA and proteinase inhibitors. Gu-EDTA extracts were desalted and used for the following assays: (1) bone cell proliferation in chick calvarial cell mitogenic assay using the incorporation of [3H]thymidine into TCA-insoluble material; (2) osteocalcin by radioimmunoassay (RIA); (3) insulin-like growth factor I (IGF-I) by RIA; (4) skeletal growth factor/insulinlike growth factor II (SGF/IGF-II) by radioreceptor assay; and (5) transforming growth factor beta (TGF-beta) by bioassay. Gu-EDTA extracts stimulated bone cell proliferation. At 10 micrograms/ml, dentin proteins increased the incorporation of [3H]thymidine by calvarial cells to 320% of that by BSA-treated control cells. Consistent with the presence of mitogenic activity, growth factors were found in dentin in the following concentrations (ng/micrograms Gu-EDTA protein): (1) IGF-I, 0.06; (2) SGF/IGF-II, 0.52; and (3) TGF-beta, 0.017. All three growth factors were present in concentrations lower than that found in human bone. Osteocalcin was detected at a concentration of 3.0 mg/g Gu-EDTA protein, also much lower than that in bone.

To determine whether the nonsteroidal antiestrogen tamoxifen behaves as either an agonist or antagonist of estrogen on bone, the effects of ovariectomy, 17 beta-estradiol, and tamoxifen were compared on radial growth at the tibial diaphysis in young adult female rats. Ovariectomy and 17 beta-estradiol did not alter serum calcium, phosphate, or 25-hydroxyvitamin D. Ovariectomy increased serum 1,25-dihydroxyvitamin D in one experiment but not in the other. Tamoxifen increased the serum calcium and phosphate by itself and did not change serum 1,25-dihydroxyvitamin D in ovariectomized rats. Ovariectomy produced significant increases in medullary area, periosteal bone formation rate, and periosteal bone apposition rate compared to values in sham-operated animals and did not change endosteal bone formation rate. The increase in medullary area resulted from an increase in osteoclast number and resorbing surface length. Although endosteal forming surface length decreased, this was compensated for by an increase in the apposition rate. 17 beta-estradiol and tamoxifen each prevented the increases in bone formation rate and medullary area in ovariectomized rats. Tamoxifen reduced the length of the resorbing surface and osteoclast number to values observed in sham-operated animals. The findings demonstrate that in the rat, tamoxifen acts as an estrogen agonist by preventing the skeletal alterations that result from ovarian hormone deficiency.

Research Article| January 01 1989 Phosphotyrosyl protein phosphatases K H W Lau; K H W Lau 1Department of Medicine and Biochemistry, Loma Linda University, and Mineral Metabolism Unit (151), Jerry L. Pettis Memorial Veterans' Hospital, Loma Linda, CA 92357, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar J R Farley; J R Farley 1Department of Medicine and Biochemistry, Loma Linda University, and Mineral Metabolism Unit (151), Jerry L. Pettis Memorial Veterans' Hospital, Loma Linda, CA 92357, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar D J Baylink D J Baylink 1Department of Medicine and Biochemistry, Loma Linda University, and Mineral Metabolism Unit (151), Jerry L. Pettis Memorial Veterans' Hospital, Loma Linda, CA 92357, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar Biochem J (1989) 257 (1): 23–36. https://doi.org/10.1042/bj2570023 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share MailTo Twitter LinkedIn Cite Icon Cite Get Permissions Citation K H W Lau, J R Farley, D J Baylink; Phosphotyrosyl protein phosphatases. Biochem J 1 January 1989; 257 (1): 23–36. doi: https://doi.org/10.1042/bj2570023 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Journal Search Advanced Search This content is only available as a PDF. © 1989 London: The Biochemical society1989 Article PDF first page preview Close Modal You do not currently have access to this content.

We determined the skeletal content of insulin-like growth factor-I (IGF-I) and transforming growth factor-beta (TGF beta) in human bone as a function of age, using 66 samples of femoral cortical bone obtained from 46 men and 20 women between the ages of 20-64 yr. We found a linear decline in the skeletal content of IGF-I (nanograms per mg protein) with donor age (r = -0.43; P < 0.001) in the total population. The skeletal content of TGF beta also decreased with age (i.e. 1/TGF beta vs. age; r = 0.28; P < 0.02) for the total population. We did not observe any difference in the skeletal growth factor content between male and female donors. IGF-I content, when analyzed by decade divisions of age, showed a reduction between the 20- to 29-yr-old and the 50- to 59-yr-old subjects (P < 0.02). The loss rate of IGF-I was 1.56 ng/mg protein.yr, corresponding to a net loss of 60% of skeletal IGF-I between the ages of 20-60 yr. The loss rate of TGF beta was 0.03 ng/mg protein.yr, corresponding to a net loss of 25% of the skeletal TGF beta between the ages of 20-60 yr.

Lipid analyses of the human immunodeficiency virus (HIV) propagated in Hut 78 cells indicated a low total lipid/protein ratio, a high cholesterol/phospholipid molar ratio, and major phospholipids consisting of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylserine; comparable lipid profiles were noted for human erythrocytes and other RNA viruses. Electron spin resonance (ESR) studies of HIV labeled with 5-nitroxide stearate (N-oxy-4',4'-dimethyloxazolidine derivative of ketostearate) showed a low "fluidity" at 37 degrees C, similar to other enveloped RNA viruses and erythrocytes and probably due to the high cholesterol/phospholipid ratio. Ethanol (50%) completely disrupts the envelope, contributing to the rapid inactivation of HIV by ethanol. Contrarily, heating to 57 degrees C causes much less fluidization, and this heating may play a role in the slower viral inactivation at high temperatures. Should a critical minimum ordering in the HIV envelope be necessary for viral stability and infectivity, manipulating the lipid composition or fluidizing the HIV membrane, or both, may provide an untried therapeutic approach.

The effects of castration on bone histomorphometry and mineral homeostasis were compared in male and female rats. Measurements were performed 4 weeks after sham operation or gonadectomy. Orchiectomy produced increases in serum calcium and decreases in serum testosterone and androstenedione, whereas ovariectomy produced decreases in serum estradiol and testosterone. Orchiectomy did not alter static bone histomorphometric measurements of the tibial diaphysis, whereas ovariectomy increased cross-sectional and medullary areas, lowered endosteal tetracycline-labeled surface length, and markedly increased endosteal nonlabeled surface length. Orchiectomy decreased mean periosteal bone formation rate and mean periosteal bone apposition rate, whereas ovariectomy increased both measurements. Orchiectomy and ovariectomy markedly diminished trabecular area and trabecular surface length at the tibial metaphysis. Orchiectomy did not alter the number of osteoclasts per mm trabecular surface or the percentage of trabecular surface covered by osteoclasts, whereas ovariectomy increased both measurements. These findings indicate that gonadal hormones produce separate and distinct effects on bone metabolism as determined by histomorphometry in male and female rats.

Elderly women are at increased risk for bone loss and fractures. In previous cross-sectional and longitudinal studies of women residing in northern latitudes, bone loss was most pronounced during winter months and in those consuming less than 1 g calcium per day. In this study we sought to test the hypothesis that calcium supplementation by either calcium carbonate or dietary means would prevent seasonal bone loss and preserve bone mass. Sixty older postmenopausal women without osteoporosis were randomized to one of three treatment arms: Dietary milk supplementation (D-4 glasses of milk/day), Calcium carbonate (CaCO3-1000 mg/day in two divided doses), or placebo (P). After 2 yr, placebo-treated women consumed a mean of 683 mg/day of calcium and lost 3.0% of their greater trochanteric (GT) bone mineral density (BMD) (P < 0.03 vs. baseline); Dietary supplemented women averaged a calcium intake of 1028 mg/day and sustained minimal loss from the GT (-1.5%; P = 0.30), whereas CaCO3-treated women (total Ca intake, 1633 mg/day) suffered no bone loss from the GT and showed a significant increase in spinal and femoral neck BMD (P < 0.05). Femoral bone loss occurred exclusively during the two winters of the study (i.e. total loss, -3.2%; P < 0.02 in placebo-treated women) with virtually no change in GT BMD during summer. Serum 25-OH vitamin D declined by more than 20% (P < 0.001) in all groups during the winter months but returned to baseline in summer; PTH levels rose approximately 20% (P < 0.001) during winter but did not return to baseline during the summers. Urine N-telopeptide and osteocalcin levels increased significantly but only in the P-treated women and only during winter. Serum insulin growth factor binding protein 4, an inhibitory insulin growth factor binding protein, rose 15% (P < 0.03) from summer to winter, but this increase was significant only in those women consuming <1000 mg/day of calcium. By multivariate analysis, total calcium intake was the strongest predictor of bone loss from the hip. Urinary N-telopeptide also closely correlated with GT BMD but only during winter (P = 0.003). We conclude that calcium supplementation prevents bone loss in elderly women by suppressing bone turnover during the winter when serum 25-OH vitamin D declines and serum PTH increases. The precise amount of calcium necessary to preserve BMD in elderly women requires further studies, although in this study, at least 1000 mg/day of supplemental calcium was adequate prophylaxis against femoral bone loss.

Based on an evolutionary theory of socialization, Belsky and colleagues proposed that girls exposed to a stressful environment, especially when due to father absence in the first 7 years of life, showed an early onset of puberty, precocious sexuality, and unstable relationships as adults. The authors of this article examined an alternative explanation that a variant X-linked androgen receptor (AR) gene, predisposing the father to behaviors that include family abandonment, may be passed to their daughters causing early puberty, precocious sexuality, and behavior problems. The results of a study of 121 White males and 164 White females showed a significant association of the short alleles of the GGC repeat polymorphism of the AR gene with a range of measures of aggression and impulsivity, increased number of sexual partners, sexual compulsivity, and lifetime number of sex partners in males; and paternal divorce, father absence, and early age of menarche in females. These findings support a genetic explanation of the Belsky psychosocial evolutionary hypothesis regarding the association of fathers' absence and parental stress with early age of onset of menarche and early sexual activity in their daughters. A genetic explanation of the father absence effect is proposed in which fathers carrying the AR alleles are more likely to abandon a marriage (father absence) and pass those alleles to their daughters in whom they produce an earlier age of menarche and behavioral problems.

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] induces differentiation and inhibits proliferation in many cell types including bone cells. These effects may be mediated by the modulation of the insulin-like growth factor (IGF) regulatory system. Therefore we investigated the effects of 1,25-(OH)2D3 on transcript and protein levels of both IGF-I and IGF binding proteins (IGFBPs) in clonal mouse osteoblasts. Subconfluent cultures were treated in serum-free medium with 1,25-(OH)2D3. Secreted IGF-I was measured using a RIA under conditions eliminating the interference of IGFBPs. 1,25-(OH)2D3 (10(-11)-10(-8) M) inhibited IGF-I release in a dose dependent manner at 24 h (maximally to 30 +/- 5% of control, mean +/- SEM of seven independent experiments). In a time course study IGF-I increased in the media of control cultures over a 48-h period, while IGF-I secretion was completely prevented from 6 h onward in 1,25-(OH)2D3 treated cultures. Northern blot analysis revealed four IGF-I transcripts of 0.9, 1.8, 4.4, and 7.5 kilobases (kb). 1,25-(OH)2D3 decreased levels of the 7.5 kb IGF-I transcript from 4-48 h, with maximal inhibition occurring at 24 h (25% of control). Western ligand blots of the culture medium demonstrated secretion of a 25-kilodalton IGFBP, which comprised greater than or equal to 90% of the secreted IGFBPs. The 25-kilodalton IGFBP had previously been shown to have sequence similarity with IGFBP-4, a binding protein which inhibits the action of IGFs on bone cells. 1,25-(OH)2D3 treatment increased secretion of IGFBP-4 up to 14-fold over 24 h. 1,25-(OH)2D3 also increased IGFBP-4 (2.2 kb) transcript levels within 30 min, with the maximal stimulation of 8-fold occurring after 8 h. [3H]Thymidine incorporation into cells was inhibited by 1,25-(OH)2D3 both under basal and serum-stimulated conditions. Our results are consistent with the hypothesis that the effects of 1,25-(OH)2D3 on osteoblast proliferation may be mediated in part by decreased levels of IGF-I and increased concentrations of inhibitory IGFBP-4. It is proposed that this alteration in the IGF system may be an important functional autocrine or paracrine switch in the transition of osteoblasts from states of proliferation to differentiation.

A tartrate-resistant acid phosphatase (TrACP), which has been suggested to be very similar to the osteoclastic TrACP, was partially purified from the spleen of a patient with hairy cell leukemia. The purification procedure consisted of carboxymethyl-Sepharose, phosphocellulose, Sephacryl S-200, and phenyl-Sepharose chromatographies. Polyclonal antibodies were generated in guinea pigs with a titer of at least 1:6000. Immunohistochemical staining of fetal rat tibia with the antisera revealed that only the lysosomes of osteoclasts, but not osteoblasts, were stained. An enzyme-linked immunosorbent assay (ELISA) was developed with the antisera. There was no cross-reactivity with 1) partially purified acid phosphatases (ACPs) from normal human and beef spleens, 2) ACPs in extracts of human osteoblastic cells, 3) purified bovine bone matrix TrACP, or 4) commercial prostatic ACP. However, extracts of giant cell bone tumors, containing large amounts of bona fide osteoclasts, showed large amounts of cross-reactive material, which diluted in parallel with the partially purified hairy cell leukemic TrACP in the ELISA. Commercial serum band 5b TrACP also displaced in parallel with the partially purified hairy cell leukemic TrACP. Immunoblotting studies revealed that the antiserum, but not nonimmune guinea pig serum, reacted with the homogeneous hairy cell leukemia splenic band 5 TrACPs, which were recently purified by our laboratory. Preliminary application of the ELISA to sera of patients with metabolic bone diseases revealed that normal healthy individuals had measurable amounts of the immunoreactive material, and patients with Paget's disease or hyperparathyroidism, who should have high bone turnover, had elevated levels of this immunoreactive material in their sera. In contrast, the level of serum osteoclastic TrACP in a patient with an acute lymphatic leukemia was normal. In summary, 1) we have shown that hairy cell leukemia splenic TrACP shares significant immunological similarity with the osteoclastic TrACP and with the serum band 5b TrACP, and 2) the ELISA holds promise for a sensitive and specific assay for bone resorption.

In vitro exposure to low-energy, combined magnetic fields (CMF) increased the release of insulin-like growth factor (IGF)-II from human TE-85 osteosarcoma cells. Short-term CMF exposure of only 10 min increased IGF-II levels in conditioned medium 1 h post CMF exposure. IGF-II levels were measured with a radioreceptor assay using H-35 cells that contain abundant IGF-II but not IGF-I receptors. This assay also uses a recently validated BioGel P-10 acid gel filtration method to remove IGF binding protein before quantitation of either IGF-I or IGF-II. In addition to an increase in IGF-II levels, DNA synthesis, as an index of cell proliferation, was increased during the 24-h period post CMF exposure. A monoclonal antibody against IGF-II blocked the increase in cell proliferation following CMF exposure, whereas a control monoclonal antibody against osteocalcin did not attenuate the mitogenic action of CMF exposure. The effect of CMF exposure to increase both cell proliferation and IGF-II was cell-density dependent with greater stimulation by CMF observed at lower densities. Together, these data are consistent with the hypothesis that CMF exposure stimulates release/production of IGF-II from bone cells and that increased IGF-II then promotes an increase in cell proliferation.

The removal of interproximal plaque was compared using a standard toothbrush alone, a toothbrush with unwaxed dental floss and a toothbrush with an interdental brush. 30 previously treated periodontal patients were given the cleaning aids in a three-way crossover study design. After each 1 month trial period, scores for gingivitis, buccal/lingual plaque and proximal plaque were recorded. Mean GI scores for subjects were 0.37 using the toothbrush only, 0.36 using the toothbrush with floss and 0.32 using the toothbrush with the interdental brush. Mean buccal/lingual plaque scores were 0.64 using the toothbrush only, 0.62 using the toothbrush with floss and 0.51 using the toothbrush with the interdental brush. Mean plaque scores were 2.32 with the toothbrush only, 1.71 using the toothbrush with floss and 1.22 using the toothbrush with the interdental brush. Statistically significant differences were seen in proximal plaque scores between the 3 treatment groups. The results indicate that the interdental brush used in combination with a toothbrush is more effective in the removal of plaque from proximal tooth surfaces than a toothbrush used alone or in combination with dental floss.

The effects of fluoride (20 mumol/L) and bovine bone extract (17 micrograms/ml) were determined on cultures of human bone cells, embryonic chick bone cells, and human skin fibroblasts. The incorporation of [3H]thymidine into DNA was measured 16 hours after the addition of factors. After three to five days treatment, Triton X-100 extracts of the cells were assayed for acid phosphatase activity, in the presence and absence of tartrate, and for alkaline phosphatase activity. Fluoride stimulated [3H]thymidine incorporation and specific activity of alkaline phosphatase in human bone cells and chick bone cells but not in human skin cells. Fluoride also stimulated the cell population doubling rate of the human bone cells with an optimum of approximately 20 mumol/L. Bovine bone extract stimulated thymidine uptake into DNA several-fold and decreased alkaline phosphatase activity in all three types of cultured cells. The specific activity of tartrate-resistant acid phosphatase was increased in bone cells but not in skin fibroblasts. These results suggest that fluoride specifically stimulates the proliferation and differentiation of osteoblasts, while the growth factors in bovine bone extract primarily stimulate proliferation of bone cells. Cultures of human bone cells respond similarly to chick calvarial cells when treated with fluoride or bovine bone extract.