Warming experiments underpredict plant phenological responses to climate change.

Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.

Calcium-41: a technology for monitoring changes in bone mineral.

The rare, long-lived radiotracer, 41Ca, measured by accelerator mass spectrometry in the urine or serum following incorporation into the bone provides an ultra-sensitive tool to assess changes in bone calcium balance in response to an intervention. Changes in bone balance can be followed for years with one small dose that is both radiologically and biologically non-invasive. Sequential interventions can be compared, with greater precision than they can with biochemical markers of bone turnover and with greater power than with bone densitometry. This method is especially useful to screen interventions over a period of weeks. The development and validation of this tool and its applications are reviewed. Mini abstract: Use of 41Ca measured in the urine or blood by accelerator mass spectrometry to assess bone balance provides a tool to compare the relative efficacy of multiple interventions. This perspective provides insights in the use of this novel method and comparisons with more traditional methods for evaluating the efficacy of interventions.

Validation of urinary calcium isotope excretion from bone for screening anabolic therapies for osteoporosis.

SUMMARY: Urinary excretion of calcium tracers in labeled individuals decreases in response to antiresorptive therapy, providing a tool to rapidly screen potential therapies. Using teriparatide, we demonstrate in this study that anabolic therapy also decreases tracer excretion, confirming that this method can also be used to screen potential anabolic therapies. INTRODUCTION: Changes in urinary excretion of calcium tracers from a labeled skeleton may be a rapid and sensitive method to screen potential therapies for osteoporosis. This method has been used to screen antiresorptive therapies, but the effect of anabolic therapies on tracer excretion is unknown. METHODS: Eight-month-old female Sprague Dawley rats (n = 11) were given 50 µCi (45)Ca iv. After a 1-month equilibration period, baseline urinary (45)Ca excretion and total bone mineral content (BMC) were measured. Rats were then treated with 30 µg/kg teriparatide sc per day, a bone anabolic agent, for 80 days. Urine was collected throughout the study and analyzed for (45)Ca and total Ca, and BMC was measured at the beginning and end of the study. RESULTS: Teriparatide decreased urinary (45)Ca excretion by 52.1 % and increased BMC by 21.7 %. The change in bone calcium retention as determined by the ratio of (45)Ca to total Ca excretion in urine from day 6 through 15 of teriparatide treatment was significantly correlated (p = 0.036) with the change in BMC after 80 days of teriparatide treatment. CONCLUSION: Urinary excretion of calcium tracers from labeled bone is an effective method to rapidly screen potential anabolic therapies for osteoporosis.

Calcium and vitamin D intake maintained from preovariectomy independently affect calcium metabolism and bone properties in Sprague Dawley rats.

UNLABELLED: The interaction of habitual Ca and vitamin D intake from preovariectomy to 4 months postovariectomy on bone and Ca metabolism was assessed. Higher Ca intake suppressed net bone turnover, and both nutrients independently benefitted trabecular structure. Habitual intake of adequate Ca and ~50 nmol/L vitamin D status is most beneficial. INTRODUCTION: Dietary strategies to benefit bone are typically tested prior to or after menopause but not through menopause transition. We investigated the interaction of Ca and vitamin D status on Ca absorption, bone remodeling, Ca kinetics, and bone strength as rats transitioned through estrogen deficiency. METHODS: Sprague Dawley rats were randomized at 8 weeks to 0.2 or 1.0 % Ca and 50, 100, or 1,000 IU (1.25, 2.5, or 25 µg) vitamin D/kg diet (2 × 3 factorial design) and ovariectomized at 12 weeks. Urinary (45)Ca excretion from deep-labeled bone was used to assess net bone turnover weekly. Ca kinetics was performed between 25 and 28 weeks. Rats were killed at 29 weeks. Femoral and tibiae structure (by µCT), dynamic histomorphometry, and bone Ca content were assessed. RESULTS: Mean 25(OH)D for rats on the 50, 100, 1,000 IU vitamin D/kg diet were 32, 54, and 175 nmol/L, respectively. Higher Ca intake ameliorated net bone turnover, reduced fractional Ca absorption and bone resorption, and increased net Ca absorption. Tibial and femoral trabecular structures were enhanced independently by higher Ca and vitamin D intake. Tibial bone width and fracture resistance were enhanced by higher vitamin D intake. Dynamic histomorphometry in the tibia was not affected by either nutrient. A Ca × vitamin D interaction existed in femur length, tibial Ca content, and mass of the soft tissue/extracellular fluid compartment. CONCLUSIONS: Adequate Ca intake and serum 25(OH)D level of 50 nmol/L provided the most benefit for bone health, mostly through independent effects of Ca and vitamin D.

Microbial community structure during fluoranthene degradation in the presence of plants.

AIMS: To investigate bacterial and fungal community structure during degradation of varying concentrations (0-5000 mg kg(-1) ) of the polycyclic aromatic hydrocarbon (PAH) fluoranthene in the presence or absence of tomato plants. METHOD AND RESULTS: Fluoranthene amended or unamended growing media, with or without a plant, were incubated in pots in a glasshouse for 30 days. Fluoranthene concentration was quantified using GC-FID, while bacterial and fungal community structure was investigated using trflp and arisa, respectively. The abundance of two ring hydroxylating dioxygenase genes was measured using qPCR. More fluoranthene was degraded in the presence of tomato plants at 500 and 5000 mg fluoranthene kg(-1) (P < 0·001), and it had a toxic effect on plant growth. Bacterial and fungal community composition in the rhizosphere was significantly different from that in nonrhizospheric and unplanted samples. The influence of fluoranthene on bacterial communities overcame that of the plant root such that community composition in rhizosphere and planted nonrhizospheric samples was broadly similar when fluoranthene was present. PAH-RHDα-GP genes were more abundant than PAH-RHDα-GN genes in all treatments. PAH-RHDα-GN abundance was unaffected by either PAH concentration or growing medium type, while the abundance of PAH-RHDα-GP was greatest in the rhizosphere. CONCLUSIONS: Plants promoted microbial growth and diversity and led to increases in abundance of Gram-positive dioxygenase genes, correlated with increased degradation of fluoranthene. SIGNIFICANCE AND IMPACT OF THE STUDY: This work contributes to knowledge in the broad area of biodegradation and also provides useful information for the design of future bioremediation strategies.

Validation of a simple isotope method for estimating true calcium fractional absorption in adolescents.

UNLABELLED: We validated a single oral isotope method for estimating fractional calcium absorption determined by double isotope methods in adolescents. Developed equations with an oral isotope including a single blood draw or spot urine collection can be used to evaluate fractional calcium absorption in adolescents which allows flexibility in developing protocols. INTRODUCTION: This study was designed to develop and validate a simpler, less expensive single oral isotope method for determining fractional calcium (Ca) absorption in adolescents. METHODS: We used our database of 31 observations from ten white and 12 black adolescent girls aged 10-15 years who participated in metabolic and kinetic studies. Tracer data following oral ((44)Ca) and intravenous (IV, (42)Ca) administration of calcium stable isotopes and samples in serum and urine from various time points up to 4 days were used to develop methods using multiple regression analysis based on a single measurement of enriched stable isotope/tracee defined as tracer/tracee (TT) in serum (TT(serum)) or urine (TT(urine)). Reference values for fractional calcium absorption were from oral/IV stable isotope ratios in 24-h serum or urine and full kinetic modeling. RESULTS: The strongest equation using a single blood sample had R (2) = 0.94 (p < 0.001): fractional Ca absorption = 1.3340(4-h TT(serum))(0.7872) BSA(1.7132)e ((-0.01652 PMA)), where BSA is body surface area and PMA is post-menarcheal age. The strongest equation using a single urine sample had R (2) = 0.95 (p < 0.001): fractional Ca absorption = 2.3088 (5-12 h TT(urine))(0.8208) BSA(1.5260)e ((-0.01850 PMA)). Equations were also developed with Tanner score. An external data set of Asian adolescent boys and girls was used to validate the equations. CONCLUSION: Equations using an oral isotope and a single blood draw or urine collection for determining fractional calcium absorption were successfully validated in healthy, non-obese white and black adolescent girls aged 10-15 years. The equations well-predicted fractional calcium absorption in Asian adolescent boys and girls.

Simple isotopic method using oral stable or radioactive tracers for estimating fractional calcium absorption in adult women.

UNLABELLED: We extended a simple oral method for estimating fractional calcium absorption determined by double isotopic methods using radioactive or stable isotope across wide age of adult women. Fractional calcium absorption can be estimated by using either a radioactive or stable oral isotope across the entire age spectrum of adult women. INTRODUCTION: A method for estimating fractional calcium absorption using a single serum collection following a single oral radioactive isotopic tracer has been validated against a classical double isotopic tracer ratio method in adults. Our goal was to extend this simplified method to include use of stable isotopes and a broad age range. METHODS: We used our database of 56 observations from 26 white adult women aged 19-67 years receiving either radioactive or stable isotopes. Reference values for fractional calcium absorption were determined from 24-h double isotopic ratios in serum and urine and from full kinetic modeling. RESULTS: Equations for estimating fractional calcium absorption were developed from isotopic enrichment in serum and urine from an oral tracer and measures of body size using the multiple linear regression analysis. Equations using a 4- to 6-h sample following an oral dose of either a stable or radioactive isotope corrected for body size were highly correlated with the reference values for fractional calcium absorption across different aged populations (r > 0.8, p < 0.001). CONCLUSION: Fractional calcium absorption can be estimated by a single oral tracer method using either radioactive or stable calcium isotopes across the entire age spectrum in healthy white adult women.

Bone-seeking labels as markers for bone turnover: validation of urinary excretion in rats.

UNLABELLED: Urinary excretion of tritiated tetracycline ((3)H-TC) and (41)Ca tracers was validated as reflecting skeletal disappearance of these bone-seeking tracers as a direct measure of bone turnover following ovariectomy in rats. INTRODUCTION: Tritiated tetracycline ((3)H-TC) and Ca tracers have been used to measure bone resorption in animal models, but urinary excretion of these labels has not been directly compared to skeletal turnover. We aimed to evaluate the use of bone-seeking labels by comparing label release into urine with label in the skeleton when bone turnover was perturbed following ovariectomy. METHODS: Sixty-four 6-month-old ovariectomized (OVX) rats were randomized to one of eight groups in a 2 × 4 design that differed in time of (3)H-TC and (41)Ca administration following ovariectomy (1 month, when bone turnover would be accelerated following estrogen depletion or 3 months when bone loss due to OVX had slowed down) and time of euthanasia (1 week, 1 month, 3 months, and 6 months post-dose). Twenty-four-hour urine pools over two to four consecutive days and total skeleton were collected and recovered for the assessment of (3)H-TC and (41)Ca. RESULTS: Urinary (3)H-TC levels reflected skeletal (3)H-TC levels (r = 0.93; p < 0.0001) over a wide range of bone turnover rates in response to an intervention. Urinary (41)Ca and (3)H-TC excretion were highly correlated (r = 0.95, p < 0.0001). CONCLUSION: This study confirms that bone-seeking label excretion into the urine directly measures bone turnover.

Expression of c-fos and AP-1 activity in senescent human fibroblasts is not sufficient for DNA synthesis.

Human fibroblasts have a limited replicative life span when maintained in culture after which they become unresponsive to treatment with mitogens, a phenomenon most commonly called senescence. Experiments indicating that serum does not induce expression of the c-fos proto-oncogene in senescent fibroblasts raised the issue of a potential central role for c-fos in the phenotype of sustained growth arrest. This was directly tested by microinjection of oncogenic c-Ha-ras protein into senescent fibroblasts. While ras injection was found to induce marked nuclear c-fos expression and functional AP-1 transcription activity, this did not lead to DNA synthesis. These results suggest that the senescence phenotype cannot be solely attributed to the absence of c-fos expression and that the proliferative block in these cells is either independent of AP-1 transcriptional activity, downstream of it, or involves multiple molecular mechanisms.

Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca.

INTRODUCTION: The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments. METHODS: Thirteen postmenopausal women (>or=6 yr since menopause) were predosed with 41Ca iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for 41Ca/Ca analysis by accelerator mass spectrometry. RESULTS: Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary 41Ca/Ca ratios. CONCLUSIONS: Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary 41Ca excretion from prelabeled bone.

Simple aspiration versus intercostal tube drainage for primary spontaneous pneumothorax in adults.

BACKGROUND: In the management of primary spontaneous pneumothorax, simple aspiration is technically easier to perform. A systematic review may better define the clinical effectiveness and safety of simple aspiration compared to intercostal tube drainage in the management of primary spontaneous pneumothorax. OBJECTIVES: To compare the clinically efficacy and safety of simple aspiration and intercostal tube drainage in the management of primary spontaneous pneumothorax. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 2, 2006), MEDLINE (1966 to August 2006), and EMBASE (1980 to August 2006). We searched Current Controlled Trials metaRegister of Clinical Trials (compiled by Current Science) (August 2006). We checked the reference lists of trials and contacted trial authors . We imposed no language restriction. SELECTION CRITERIA: Randomized controlled trials comparing simple aspiration with intercostal tube drainage in adults aged 18 and over with primary spontaneous pneumothorax. DATA COLLECTION AND ANALYSIS: Two authors independently assessed trial quality and extracted data. No statistical methods were necessary because only one study met the inclusion criteria. MAIN RESULTS: Of the 1239 publications obtained from the search strategy, we examined six studies. Five studies were excluded, and one study of 60 participants was eligible for inclusion. There was no difference in immediate success rate of simple aspiration when compared with intercostal tube drainage in the management of primary spontaneous pneumothorax (relative risk (RR) = 0.93; 95% confidence interval (CI) 0.62 to 1.40). There was no significant difference in the early failure rate between the two interventions: RR 1.12 (95% CI 0.59 to 2.13). Simple aspiration reduced the proportion of patients hospitalized (RR = 0.52; 95% CI 0.36 to 0.75). There was no significant difference between the two interventions with regard to the following outcome measures: duration of hospitalization (weighted mean difference = 1.09; 95% CI 2.18 to 0.00); number of participants undergoing any procedure for lung pleurodesis within one year (RR = 0.95; 95% CI 0.41 to 2.22);and one year success rate (RR = 1.02; 95% CI 0.75 to 1.38). AUTHORS' CONCLUSIONS: There is no significant difference between simple aspiration and intercostal tube drainage with regard to: immediate success rate, early failure rate, duration of hospitalisation, one year success rate and number of patients requiring pleurodesis at one year. Simple aspiration is associated with a reduction in the per cent of patients hospitalized when compared with intercostal tube drainage.

Using functional data analysis to summarise and interpret lactate curves.

John Tukey used the term exploratory data analysis (EDA) to describe a philosophy for analyzing data where graphical and numerical summaries are used to uncover interesting structures. The applied statistician today has a much more sophisticated set of methods to use when applying the EDA philosophy. One such collection of methods is functional data analysis (FDA), which was used to explore the structure of lactate curves. A principal components analysis and plots of the second derivatives provide new intuitive endurance markers which correlates highly with other numerical summaries of lactate curves that have been suggested in the literature.

Effects of subclinical infection on plasma retinol concentrations and assessment of prevalence of vitamin A deficiency: meta-analysis.

BACKGROUND: Vitamin A deficiency adversely affects child morbidity and survival. This deficiency is estimated by measurement of plasma retinol concentrations, but because plasma retinol is reduced by clinical and subclinical infection, this proxy measure can lead to overestimation. Infection and trauma are accompanied by rises in concentrations of acute-phase proteins in plasma. We aimed to estimate vitamin A deficiency more accurately by measuring changes in plasma retinol and acute-phase proteins associated with subclinical infection or convalescence. METHODS: We analysed data for concentrations of plasma retinol and one or more acute-phase proteins (alpha1-acid-glycoprotein, alpha1-antichymotrypsin, C-reactive protein, or serum amyloid A) from 15 studies of apparently healthy individuals. We generated summary estimates of differences in retinol concentrations for incubation, early, and late convalescent phases of infection between people with none and those with one or more raised acute-phase proteins. We compared these groups in two, three, and four group analyses. We also compared a subgroup of apparently healthy preschool (1-5 years) children with results from all other studies. FINDINGS: For all four proteins, retinol values were much higher in people with normal concentrations of protein, than in individuals with raised concentrations (16% higher for alpha1-antichymotrypsin, 18% for alpha1-acid-glycoprotein, 25% for C-reactive protein, and 32% for serum amyloid A). Estimates of the reduction in plasma retinol for individuals with infection compared with healthy individuals, were 13% (incubation), 24% (early convalescent), and 11% (late convalescent). Estimates of vitamin A deficiency in individuals with no raised acute-phase proteins (healthy group) were much the same as those obtained by adjustment of plasma retinol concentrations in the whole group using acute-phase proteins. INTERPRETATION: We recommend that surveys to estimate vitamin A deficiency should include measurements of serum C-reactive protein and alpha1-acid-glycoprotein concentrations. Information about acute-phase proteins will enable plasma retinol concentrations to be corrected where sub-clinical infection exists, and the healthy sub-group to be identified.

Predicting toxicity equivalents in fish tissue.

Toxicity equivalents is a measure of "dioxin-like" toxicity contributed by polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (dioxins), and polychlorinated dibenzofurans (furans). Calculation of toxicity equivalents require the use of analytical procedures that are expensive and slow, making them impractical for routine analysis. U.S. Environmental Protection Agency National Fish Tissue Study (2003) data were used to determine the most significant predictors of toxicity equivalents with multiple regression analysis. The strongest predictive model (P < 0.0001, R2 = 0.97) included five compounds (PCB-118; PCB-126; 2,3,7,8-TCDD; 1,2,3,6,7,8-HxCDD; 2,3,4,7,8-PeCDF). However, the required lower limit of detection for an analytical method measuring these congeners is 0.1 ppt and would not provide much benefit over the current analytical method. An alternative model (P < 0.0001, R2 = 0.68) that included three PCBs (PCB-138, PCB-153, PCB-118) would require a limit of detection of 1,000 ppt and be more practical. This research demonstrates that the measurement of selected compounds can be used to estimate toxicity equivalents and consequently serve as the impetus for the development of lower cost, rapid analytical methods for analysis of fish.

Marrow-derived cells populate scaffolds composed of xenogeneic extracellular matrix.

INTRODUCTION: The source of cells that participate in wound repair directly affects outcome. The extracellular matrix (ECM) and other acellular biomaterials have been used as therapeutic scaffolds for cell attachment and proliferation and as templates for tissue repair. The ECM consists of structural and functional proteins that influence cell attachment, gene expression patterns, and the differentiation of cells. OBJECTIVE: The objective of this study was to determine if the composition of acellular matrix scaffolds affects the recruitment of bone marrow-derived cellular elements that populate the scaffolds in vivo. METHODS: Scaffolds composed of porcine tissue ECM, purified Type I collagen, poly(L)lactic coglycolic acid (PLGA), or a mixture of porcine ECM and PLGA were implanted into subcutaneous pouches on the dorsum of mice. The origin of cells that populated the matrices was determined by first performing bone marrow transplantation to convert the marrow of glucose phosphate isomerase 1b (Gpi-1(b)) mice to cells expressing glucose phosphate isomerase 1a (Gpi-1(a)). RESULTS: A significant increase in Gpi-1(a) expressing cells was present in sites implanted with the porcine ECM compared to sites implanted with either Type I collagen or PLGA. Use of recipient mice transplanted with marrow cells that expressed beta-galactosidase confirmed that the majority of cells that populated and remodeled the naturally occurring porcine ECM were marrow derived. Addition of porcine ECM to the PLGA scaffold caused a significant increase in the number of marrow-derived cells that became part of the remodeled implant site. CONCLUSION: The composition of bioscaffolds affects the cellular recruitment pattern during tissue repair. ECM scaffolds facilitate the recruitment of marrow-derived cells into sites of remodeling.

Peak bone mass in young women.

Increasing peak bone mineral density (BMD) or content (BMC) in young women may help to reduce the incidence of osteoporosis. Identifying the age when peak bone content or density is attained is essential to develop strategies aimed at optimizing peak BMD and BMC. Total body bone mineral density (TBBMD) and content (TBBMC) were measured by a dual X-ray absorptiometer in healthy females (n = 247, aged 11-32 years). TBBMD and TBBMC were modeled separately as a nonlinear function of age. By age 22.1 +/- 2.5 years, 99% of peak BMD is attained, and by age 26.2 +/- 3.7 years, 99% of peak BMC is attained. Nonlinear relationships between weight and TBBMD or TBBMC were also modeled. In this model, the influence of several parameters, including age, weight, and height, on BMC and BMD were simultaneously assessed. A model with age and weight described the best fit for TBBMD, whereas age, weight, and height described the best fit for total body TBBMC.

Quantification of biochemical markers of bone turnover by kinetic measures of bone formation and resorption in young healthy females.

The quantification of biochemical markers of bone formation and resorption with kinetic measures of bone turnover is an essential step in their validation. Some biochemical markers have been validated by quantification against formation and resorption rates measured by calcium kinetics in adults with bone disease. However, none has been validated in healthy individuals who are undergoing skeletal growth and bone consolidation. Therefore, we have measured biochemical markers of bone formation (serum osteocalcin [OC], bone-specific alkaline phosphatase [BAP], and total alkaline phosphatase [ALP]) and resorption (serum tartrate resistant acid phosphatase [TRAP], urinary cross-linked N teleopeptides of type I collagen/creatinine [NTx/Cr], and hydroxyproline/creatinine [OHP/Cr]) in healthy females aged 11-32 years (n = 31) after an overnight fast to determine their relationship with bone formation (Vo+) and bone resorption (Vo-) as measured by calcium kinetics and balance. All biochemical markers were highly intercorrelated (r > 0.6, p < 0.001) as were Vo+ and Vo- (r = 0.91, p < 0.001). Highly significant correlations were present between bone formation measured by calcium kinetics (Vo+) and serum levels of bone biochemical markers (OC, r = 0.82, p = 0.001; ALP, r = 0.92, p = 0.001; and BAP, r = 0.90, p = 0.001) and between bone resorption measured by calcium kinetics (Vo-) and fasting serum levels and urine creatinine ratios of biochemical markers (TRAP, r = 0.77, p < 0.001; OHP/Cr, r = 0.79, p < 0.001; and NTx/Cr, r = 0.70, p < 0.001). Thus, biochemical markers of bone formation and resorption can be used to predict calcium kinetic rates during skeletal growth and the early years of formation of peak bone mass, ages at which strategies to build peak bone mass are important. Biochemical markers of formation and resorption are equally useful in predicting either the bone formation rate or the resorption rate.

Racial differences in bone turnover and calcium metabolism in adolescent females.

Blacks develop a higher peak bone mass than whites which is associated with a reduced risk for bone fracture. The physiological basis for the difference in bone mass was investigated by metabolic balance and calcium kinetic studies in adolescent black and white girls. The hypothesis that the greater peak bone mass in blacks compared with whites is due to suppressed bone resorption was tested. Subjects were housed in a supervised environment for 3 wk during which time they consumed a controlled diet and collected all excreta. Subjects were given stable calcium isotopes orally and intravenously after 1 wk adaptation. Blacks have greater calcium retention (mean +/- SD, 11.5 +/- 6.1 vs. 7.3 +/- 4.1 mmol/d, P < 0.05) consistent with greater bone formation rates (49.4 +/- 13.5 vs. 36.5 +/- 13.6 mmol/d, P < 0.05) relative to bone resorption rates (37.4 +/- 13.2 vs. 29.4 +/- 10.9 mmol/d, P = 0.07), increased calcium absorption efficiency (54 +/- 19 vs. 38 +/- 18%, P < 0.05) and decreased urinary calcium (1.15 +/- 0.95 vs. 2.50 +/- 1.35 mmol/d, P < 0.001), compared with whites. The racial differences in calcium retention in adolescence can account for the racial differences in bone mass of adults.

Calcium retention estimated from indicators of skeletal status in adolescent girls and young women.

To determine clinically useful predictors of calcium retention during postpubertal growth, calcium balance, bio-chemical markers of bone turnover, and anthropometric variables were determined in 14 girls aged 11-14 y and in 11 young women aged 19-30 y. Subjects participated in a 3-wk calcium-balance study with a calcium intake of 1332 mg/d. Biochemical markers of bone turnover (serum osteocalcin, total alkaline phosphatase, bone alkaline phosphatase, tartrate-resistant acid phosphatase, and urinary cross-linked N-teleopeptides of type I collagen and hydroxyproline as the creatinine ratios) were measured in fasting samples. Total-body bone mineral density and total-body calcium content were significantly higher in adults than in adolescents (1.17 compared with 1.05 g/cm2 and 1019 compared with 791 g, respectively). At the observed retention of 326 mg/d, adolescents would require 2 y to reach the total bone calcium of the young adults. All biomarkers of bone turnover were strikingly higher in adolescents than in adults and were strongly correlated with calcium retention. A multiple-regression model using a biochemical marker of bone turnover (serum osteocalcin) and postmenarcheal age (a measure of sexual maturation) described 75% of the variability in calcium retention.

Vitamin B-6 status of Egyptian mothers: relation to infant behavior and maternal-infant interactions.

Functional consequences of marginal maternal vitamin B-6 status for behavior of the neonate and for mother-infant interactions at age 3-6 mo were assessed by a double-blind procedure. In 27 of 70 Egyptian village women studied, vitamin B-6 concentration of their milk was considered indicative of poor maternal vitamin B-6 nutriture. Neonatal behavior, quantified by the Brazelton Neonatal Behavioral Assessment Scale, showed that consolability, appropriate build-up to a crying state, and response to aversive stimuli were significantly correlated with maternal vitamin B-6 nutriture. Naturalistic observational procedures, used twice monthly with infants aged 3-6 mo, indicated that mothers assessed as having marginal vitamin B-6 status were less responsive to their infants' vocalizations, showed less effective intervention to infant distress, and were more likely to use older siblings as care-givers than were mothers of better vitamin status. We conclude that vitamin B-6 was a factor influencing both the behavior of the mother and her infant.