Elucidating the effect of specific surface area on the gastrointestinal absorption of nanostructured calcium through Calcium-45 in vivo radiotracing.

Low dietary calcium intake and absorption may increase the risk of hypocalcaemia disease states. Reducing the particle size of calcium-containing powders and increasing the specific surface area (SSA), may have high oral calcium bioavailability. The absorption of a single dose of different sized calcium carbonate nanoparticles was traced in Sprague-Dawley rats with radioactive calcium-45 (half-life = 162.6 days, ß- endpoint = 258 keV; 100%). Four calcium carbonate formulations (calcium-45) were administered to Sprague-Dawley rodents (6 per treatment; n = 24). The groups were [45Ca]CaCO3 SSA 3 m2/g, [45Ca]CaCO3 36 m2/g, [45Ca]CaCO3 64 m2/g and a separate [45Ca]CaCO3 36 m2/g formulation produced by flame assisted pyrolysis. Blood and urine were sampled periodically, and organs collected and analysed after euthanasia. No changes in SSA or crystallinity were observed when powders before or after irradiation were compared. The [45Ca]CaCO3 64 m2/g formulation presented with higher levels in blood 2 h after administration and a higher liver and femur concentration. These findings suggest [45Ca]CaCO3 64 m2/g could lead to increased oral bioavailability.

Ocean acidification: synergistic inhibitory effects of protons and heavy metals on 45Ca uptake by lobster branchiostegite membrane vesicles.

Previous work with isolated outer membrane vesicles of lobster branchiostegite epithelial cells has shown that 45Ca2+ uptake by these structures is significantly (p < 0.02) reduced by an incremental decrease in saline pH (increased proton concentration) and that this decrease is due to competitive inhibition between carrier-mediated transport of 45Ca2+ and hydrogen ions. The present paper extends these previous findings and describes the combined effects of pH and cationic heavy metals on branchiostegite uptake of 45Ca2+. Partially purified membrane vesicles of branchiostegite cells were produced by a homogenization/centrifugation method and were loaded with mannitol at pH 7.0. The time course of 1 mM 45Ca2+ uptake in a mannitol medium at pH 8.5 containing 100 µM verapamil (Ca2+ channel blocker) was hyperbolic and approached equilibrium at 30 min. This uptake was either significantly reduced (p < 0.05) by the addition of 5 µM Zn2+ or essentially abolished with the addition of 5 µM Cu2+. Increasing zinc concentrations (5-500 µM) reduced 1 mM 45Ca2+ uptake at pH 8.5 or 7.5 in a hyperbolic fashion with the remaining non-inhibited uptake due to apparent non-specific binding. Uptake of 1 mM 45Ca2+ at pH 8.5, 7.5, 7.5 + Zn2+, and 7.5 + Zn2+ + Cu2+ + Cd2+ in the presence of 100 µM verapamil displayed a stepwise reduction of 45Ca2+ uptake with the addition of each treatment until only non-specific isotope binding occurred with all cation inhibitors. 45Ca2+ influxes (15 s uptakes; 0.25-5.0 mM calcium + 100 µM verapamil) in the presence and absence of 10 µM Zn2+ were both hyperbolic functions of calcium concentration. The curve with Zn2+ displayed a transport Km twice that of the control (p < 0.05), while inhibitor and control curve Jmax values were not significantly different (p > 0.05), suggesting competitive inhibition between 45Ca2+ and Zn2+ influxes. Analysis of the relative inhibitory effects of increased proton or heavy metal interaction with 45Ca2+ uptake suggests that divalent metals may reduce the calcium transport about twice as much as a drop in pH, but together, they appear to abolish carrier-mediated transport.

Palliative care of bone pain due to skeletal metastases: Exploring newer avenues using neutron activated (45)Ca.

INTRODUCTION: With an objective to develop a cost-effective radiochemical formulation for palliation of pain due to skeletal metastases, we have demonstrated a viable method for large-scale production of (45)Ca (t½=163 days, Eßmax=0.3MeV) using moderate flux research reactor, its purification from radionuclidic impurities adopting electrochemical approach and preclinical evaluation of (45)CaCl2. METHODS: Irradiation parameters were optimized by theoretical calculations for production of (45)Ca with highest possible specific activity along with minimum radionuclidic impurity burden. Based on this, the radioisotope was produced in reactor by irradiation of isotopically enriched (98% in (44)Ca) CaO target at a thermal neutron flux of ~1 × 10(14) n.cm(-2).s(-1) for 4 months. Scandium-46 impurity co-produced along with (45)Ca was efficiently removed adopting an electrochemical separation approach. The bone specificity of (45)CaCl2 was established by in vitro studies involving its uptake in hydroxyapatite (HA) particles and also evaluating its biodistribution pattern over a period of 2 weeks after in vivo administration in Wistar rats. RESULTS: Thermal neutron irradiation of 100mg of enriched (98% in (44)Ca) CaO target followed by radiochemical processing and electrochemical purification procedure yielded ~37 GBq of (45)Ca with a specific activity of ~370 MBq/mg and radionuclidic purity>99.99%. The reliability and reproducibility of this approach were amply demonstrated by process demonstration in several batches. In vitro studies indicated significant uptake of (45)CaCl2 (up to 65%) in HA particles. In vivo biodistribution studies in Wistar rats showed specific skeletal accumulation (40-46%ID) with good retention over a period of 2 weeks. CONCLUSIONS: To the best of our knowledge, this is the first study on utilization of (45)CaCl2 in the context of nuclear medicine. The results obtained in this study hold promise and warrant further investigations for future translation of (45)CaCl2 to the clinics, thereby potentially enabling a cost-effective approach for metastatic bone pain palliation especially in developing countries.

In vivo measurement of the absorption of strontium in the rumen and small intestine of sheep as an index of calcium absorption capacity.

In the present study, a method was developed for determining the alimentary tract Ca absorption capacity of ruminant animals by measuring the absorption rate of Sr after the administration of an oral dose of strontium chloride acting as a tracer analogue of Ca. A close correlation between the absorption rates of the two tracers was observed upon simultaneous administration of an oral dose of stable Sr and radioactive calcium (r 0·98). The Ca absorption capacity of the rumen and small intestine was determined separately by either directing the solution into the rumen or by diverting it into the post-ruminal tract by vasopressin-induced closure of the ruminoreticular groove. The animals were treated with 1α-hydroxyvitamin D3 administered via subcutaneously implanted mini-osmotic pumps. The effect of elevated plasma 1,25-dihydroxycholecalciferol concentrations on the Ca absorption capacity of the alimentary tract was then determined. An increased rate of Sr absorption was observed in both the rumen and small intestine of sheep after treatment, although it is unclear whether the rumen possesses the same vitamin D-dependent Ca absorption pathway as the small intestine.

Milrinone and levosimendan during porcine myocardial ischemia -- no effects on calcium overload and metabolism.

BACKGROUND: Although inotropic stimulation is considered harmful in the presence of myocardial ischaemia, both calcium sensitisers and phosphodiesterase inhibitors may offer cardioprotection. We hypothesise that these cardioprotective effects are related to an acute alteration of myocardial metabolism. We studied in vivo effects of milrinone and levosimendan on calcium overload and ischaemic markers using left ventricular microdialysis in pigs with acute myocardial ischaemia. METHODS: Anaesthetised juvenile pigs, average weight 36 kg, were randomised to one of three intravenous treatment groups: milrinone 50 µg/kg bolus plus infusion 0.5 µg/kg/min (n = 7), levosimendan 24 µg/kg plus infusion 0.2 µg/kg/min (n = 7), or placebo (n = 6) for 60 min prior to and during a 45 min acute regional coronary occlusion. Systemic and myocardial haemodynamics were assessed, and microdialysis was performed with catheters positioned in the left ventricular wall. (45) Ca(2+) was included in the microperfusate in order to assess local calcium uptake into myocardial cells. The microdialysate was analysed for glucose, lactate, pyruvate, glycerol, and for (45) Ca(2+) recovery. RESULTS: During ischaemia, there were no differences in microdialysate-measured parameters between control animals and milrinone- or levosimendan-treated groups. In the pre-ischaemic period, arterial blood pressure decreased in all groups while myocardial oxygen consumption remained stable. CONCLUSIONS: These findings reject the hypothesis of an immediate energy-conserving effect of milrinone and levosimendan during acute myocardial ischaemia. On the other hand, the data show that inotropic support with milrinone and levosimendan does not worsen the metabolic parameters that were measured in the ischaemic myocardium.

Liquid scintillation based quantitative measurement of dual radioisotopes (3H and 45Ca) in biological samples for bone remodeling studies.

Acute and prolonged bone complications associated with radiation and chemotherapy in cancer survivors underscore the importance of establishing a laboratory-based complementary dual-isotope tool to evaluate short- as well as long-term bone remodeling in an in vivo model. To address this need, a liquid scintillation dual-label method was investigated using different scintillation cocktails for quantitative measurement of (3)H-tetracycline ((3)H-TC) and (45)Ca as markers of bone turnover in mice. Individual samples were prepared over a wide range of known (45)Ca/(3)H activity ratios. Results showed that (45)Ca/(3)H activity ratios determined experimentally by the dual-label method were comparable to the known activity ratios (percentage difference ∼2%), but large variations were found in samples with (45)Ca/(3)H activity ratios in range of 2-10 (percentage difference ∼20-30%). Urine and fecal samples from mice administered with both (3)H-TC and (45)Ca were analyzed with the dual-label method. Positive correlations between (3)H and (45)Ca in urine (R=0.93) and feces (R=0.83) indicate that (3)H-TC and (45)Ca can be interchangeably used to monitor longitudinal in vivo skeletal remodeling.

In vivo stability of hydroxyapatite nanoparticles coated on titanium implant surfaces.

PURPOSE: Nanotechnology has been employed in attempts to enhance bone incorporation of dental implants. Often, nanoparticles are applied to the implant surface as particle coatings. However, the same properties that may increase the functionality may also lead to undiscovered negative effects, such as instability of the nanocoating. The aim of this study was to investigate the stability/instability of the nanoparticles using a radiolabeling technique. MATERIALS AND METHODS: Twenty threaded and turned titanium microimplants were inserted in 10 rats. All 20 implants were coated with nanometer-sized hydroxyapatite (HA) particles. In order to trace the HA nanoparticles, the particles for 16 implants were labeled with calcium 45 (45Ca). After 1, 2, 4, and 8 weeks, the implants and surrounding bone were retrieved and analyzed using autoradiography with respect to particle migration from the implant surface. Samples from the brain, liver, thymus, kidney, and blood, as well as wooden shavings from the rats' cages, were also retrieved and analyzed using liquid scintillation counting. RESULTS: The radioactivity representing the localization of 45Ca decreased over time from the vicinity of the implant. The amounts of 45Ca found in the blood and in the rats' excretions decreased with time and corresponded well to each other. After 8 weeks, the only trace of 45Ca was found in the liver. CONCLUSION: The results indicated that released particles leave the body through the natural cleaning system, and the probability that the nanocoating will assemble in vital organs and thus become a potential biologic risk factor is unlikely.

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.

Paradoxical nifedipine facilitation of 45Ca uptake into rat hippocampal synaptosomes.

Nifedipine has a high incidence of neurologic adverse reactions as compared with other dihydropyridine Cav1 (L-type) channel blockers used for treating cardiovascular diseases. The mechanism mediating neuronal excitation by nifedipine is still in debate. Nifedipine caused a dual role on veratridine-induced 45Ca uptake by rat hippocampal synaptosomes. In the nanomolar range (0.001-0.3 microM), nifedipine decreased 45Ca uptake in a cadmium-sensitive manner. In contrast with nitrendipine (0.001-10 microM), nifedipine consistently facilitated 45Ca accumulation when used in low micromolar concentrations (0.3-10 microM). The cadmium-insensitive nifedipine facilitation became less evident upon increasing veratridine concentration from 5 to 20 microM and was not detected when the synaptosomes where depolarised with 30 mM KCl. Na+ substitution by N-methyl-D-glucamine (132 mM) or blockade of Na+ currents with tetrodotoxin (1 microM) both prevented nifedipine excitation. The Na+/Ca2+-exchanger inhibitor, KB-R7943 (3-50 microM), did not reproduce nifedipine actions. Data suggest that tetrodotoxin-sensitive Na+ channels may operate paradoxical nifedipine facilitation of 45Ca uptake by rat hippocampal synaptosomes.

Association between cadmium and calcium uptake and distribution during the moult cycle of female shore crabs, Carcinus maenas: an in vivo study.

Net influxes into the haemolymph and tissue distribution of 45Ca and 109Cd were studied in vivo in female Carcinus maenas at different moult stages. Net influxes of 45Ca and 109Cd from water were higher in postmoult (A and B) C. maenas than in C3- and C4-intermoult crabs and the net influx of calcium was higher in C3-intermoult crabs than in C4-intermoult crabs. The net influxes of 45Ca and 109Cd increased in postmoult C. maenas with decreasing external calcium concentrations at constant salinity. At all external calcium concentrations a significant correlation existed between 45Ca and 109Cd accumulated in the haemolymph of individual animals. In vivo exposure of postmoult C. maenas to external lanthanum decreased the 45Ca and 109Cd uptake rates to 30 and 10%, respectively, of the control values. About 30% of injected 109Cd were found in the midgut gland, 10-20% in the gills and only a few (1-2) percent was lost to the seawater 24 h after injection. No major variations in tissue distribution of 109Cd were observed between moult stages in these tissues. Premoult crabs retained more cadmium in the haemolymph 24 h after injection than other moult stages, and postmoult crabs retained more in muscle. Between 20 and 40% of the injected 45Ca were excreted to the water, while only a few percent of the injected 45Ca were found in the soft tissues 24 h after injection. Large moult stage variations, however, were observed in the tissue distribution of internalised 45Ca. This study demonstrates that cadmium and calcium uptakes are elevated in postmoult C. maenas. The results indicate that cadmium and calcium in this stage are taken up via Ca2+-channels located in the apical membrane of gill epithelium cells. When internalised, however, cadmium and calcium are metabolised in fundamentally different ways, determined by the chemical properties and biological significance of the two metals.

In vivo and in vitro cadmium accumulation during the moult cycle of the male shore crab Carcinus maenas--interaction with calcium metabolism.

The effect of moult stage on cadmium accumulation and distribution was investigated in vivo in male shore crabs Carcinus maenas exposed to 1 mg Cd l(-1) for 7 days. The accumulation of cadmium in all tissues examined was markedly higher in postmoult (A(1-2) and B(1-2)) compared to intermoult (C1, C3 and C4) and premoult (D(0-3)). In addition, elevated levels of cadmium were found in gills of late premoult (D(2-3)) animals. The total amount of cadmium accumulated in the tissues (haemolymph, gills, midgut gland and muscle) increased from 43 microg Cd in early premoult (D(0-1)) to 391 microg Cd in late postmoult (B(1-2)). Gills and midgut gland were the primary cadmium accumulating tissues in C4-intermoult and premoult (D(0-3)); in early postmoult (A(1-2)) haemolymph and midgut gland were the main cadmium containing tissues, while midgut gland dominated in late postmoult (B(1-2)) and early intermoult (C1 and C3). A detailed account of calcium distribution in haemolymph, gills, midgut gland, muscle and exoskeleton during the moult cycle is presented. Mechanistic links between cadmium and calcium uptake in posterior gills of C4-intermoult and early postmoult (A(1-2)) crabs were explored using an in vitro gill perfusion technique. Calcium and cadmium influxes were markedly higher in postmoult compared to intermoult. No differences between intermoult and postmoult effluxes were found for either calcium or cadmium. From intermoult to postmoult net influx increased from 2.4 to 29 micromol Ca2+ g(-1) ww(gill) h(-1) and from 0.24 to 25 nmol Cd2+ g(-1) ww(gill) h(-1). The results indicate that the postmoult increase in cadmium influx is due to increased active transport of cadmium, at least partly, by accidental uptake via calcium transporting proteins. The in vitro net influx rates corresponded accurately to the observed in vivo accumulation of both cadmium and calcium. Although cadmium accumulation and distribution are clearly linked to changes in calcium requirements, cadmium did not interfere with calcium accumulation or distribution at any stage during the moult cycle.

Effects of dietary calcium and cadmium on cadmium accumulation, calcium and cadmium uptake from the water, and their interactions in juvenile rainbow trout.

The objective of this study was to examine the effects of chronically elevated dietary Ca2+ (as CaCO3), alone and in combination with elevated dietary Cd, on survival, growth, and Cd and Ca2+ accumulation in several internal compartments in juvenile rainbow trout (Oncorhynchus mykiss). In addition, effects on short-term branchial uptake and internal distribution of newly accumulated waterborne Ca2+ and Cd during acute waterborne Cd exposure (50 microg/L as CdNO3 for 3 h) were monitored using radiotracers (45Ca, 65Cd). Fish were fed with four diets: 20 mg Ca2+/g food (control), 50 mg Ca2+/g food, 300 microg Cd/g food, and 50 mg Ca2+/g + 300 microg Cd/g food for 30 days. There were no significant effects on growth, mortality, or total body Ca2+ accumulation. The presence of elevated Ca2+, Cd, or Ca2+ + Cd in the diet all reduced waterborne Ca2+ uptake in a short-term experiment (3 h), though the inhibitory mechanisms appeared to differ. The effects were marked after 15 days of feeding, but attenuated by 30 days, except when the diet was elevated in both Ca2+ and Cd. The presence of elevated Ca2+ in the diet had only modest influence on Cd uptake from the water during acute Cd challenges but greatly depressed Cd uptake from the diet and accumulation in most internal tissues. None of the treatment diets prevented the decreases in waterborne Ca2+ uptake and new Ca2+ accumulation in internal tissues caused by acute exposure to waterborne Cd. In conclusion, there are complex interactions between waterborne and dietary effects of Ca2+ and Cd. Elevated dietary Ca2+ protects against both dietary and waterborne Cd uptake, whereas both waterborne and dietary Cd elevations cause reduced waterborne Ca2+ uptake.

The effect of different mineral frames on ectopic bone formation in mouse hind leg muscles induced by native reindeer bone morphogenetic protein.

INTRODUCTION: Bone morphogenetic proteins (BMPs) require carrier material for slow release and framing material for osteoconduction. MATERIALS AND METHODS: The effect of a frame on early bone formation induced by partially purified native reindeer BMP in composite implants containing 3 mg of BMP, type IV collagen and tricalcium phosphate (TCP/Col/BMP) or hydroxyapatite (HA/Col/BMP) or biphasic tricalcium phosphate-hydroxyapatite (TCP/HA/Col/BMP) or biocoral (NC/Col/BMP) was evaluated using a mouse hind leg muscle pouch model. Collagen with native reindeer BMP (Col/BMP) and corresponding implants without native reindeer BMP served as controls. Evaluation was done by incorporation of 45Ca, radiographically and histologically 3 weeks after the implantation. RESULTS: None of the implants without native reindeer BMP were able to induce new bone visible on radiographs. The area of new bone formation in the Col/BMP (p=0.026) and TCP/HA/Col/BMP (p=0.012) groups was significantly greater than in the TCP/Col/BMP group. The optical density of the new bone area was significantly greater in the TCP/HA/Col/BMP group than in the TCP/Col/BMP (p=0.036) or Col/BMP (p=0.02) groups. 45Ca incorporation was many times greater in all the groups containing native reindeer BMP than in the corresponding groups without BMP. In the Col/BMP (p=0.046) and TCP/HA/Col/BMP (p=0.046) groups, 45Ca incorporation was significantly greater than in the TCP/Col/BMP group. No significant differences were found in any parameters between HA/Col/BMP and NC/Col/BMP groups and the other BMP-containing groups. CONCLUSIONS: Hydroxyapatite, biocoral and biphasic tricalciumphosphate-hydroxyapatite are equally good as framing material for native reindeer BMP, while tricalciumphosphate is somewhat worse. Osteoinduction of native reindeer BMP works well with collagen alone.

Effect of interleukin-1beta on NMDA-induced 45Ca2+ uptake by synaptosomes of rat brain cortex.

The effect of interleukin-1beta on presynaptic NMDA receptors was evaluated by studying NMDA-induced 45Ca2+ uptake by synaptosomes from rat brain cortex. Interleukin-1beta inhibited 45Ca2+ uptake by synaptosomes. Our results indicate that interleukin-1beta modulates presynaptic NMDA receptors and is probably involved in the regulation of synaptic transmission in the central nervous system.

Interactions between zooplankton feeding, photosynthesis and skeletal growth in the scleractinian coral Stylophora pistillata.

We investigated the effect of zooplankton feeding on tissue and skeletal growth of the scleractinian coral Stylophora pistillata. Microcolonies were divided into two groups: starved corals (SC), which were not fed during the experiment, and fed corals (FC), which were abundantly fed with Artemia salina nauplii and freshly collected zooplankton. Changes in tissue growth, photosynthesis and calcification rates were measured after 3 and 8 weeks of incubation. Calcification is the deposition of both an organic matrix and a calcium carbonate layer, so we measured the effect of feeding on both these parameters, using incorporation of (14)C-aspartic acid and (45)Ca, respectively. Aspartic acid is one of the major components of the organic matrix in scleractinian corals. For both sampling times, protein concentrations were twice as high in FC than in SC (0.73 vs 0.42 mg P(-1) cm(-2) skeleton) and chlorophyll c(2) concentrations were 3-4 times higher in fed corals (2.1+/-0.3 micro g cm(-2)). Cell specific density (CSD), which corresponds to the number of algal cells inside a host cell, was also significantly higher in FC (1.416+/-0.028) than in SC (1.316+/-0.015). Fed corals therefore displayed a higher rate of photosynthesis per unit area (P(g)(max)= 570+/-60 nmol O(2) cm(-2) h(-1) and I(k)=403+/-27 micro mol photons m(-2) s(-1)). After 8 weeks, both light and dark calcification rates were twofold greater in FC (3323+/-508 and 416+/-58 nmol Ca(2+) 2 h(-1) g(-1) dry skeletal mass) compared to SC (1560+/-217 and 225+/-35 nmol Ca(2+) 2 h(-1) g(-1) dry skeletal mass, respectively, under light and dark conditions). Aspartic acid incorporation rates were also significantly higher in FC (10.44+/-0.69 and 1.36+/- 0.26%RAV 2 h(-1) g(-1) dry skeletal mass, where RAV is total radioactivity initially present in the external medium) than in SC (6.51+/-0.45 and 0.44+/-0.02%RAV 2 h(-1) g(-1) dry skeletal mass under dark and light conditions, respectively). Rates of dark aspartic acid incorporation were lower than the rates measured in the light. Our results suggest that the increase in the rates of calcification in fed corals might be induced by a feeding-stimulation of organic matrix synthesis.

Radiocalcium absorption is reduced in postmenopausal women with vertebral and most types of peripheral fractures.

Intestinal calcium absorption accounts for 60% of the variance in calcium balance and is therefore a potentially very important determinant of bone status. Whether measured by the balance technique or with radiocalcium, it is known to be significantly reduced in postmenopausal women with vertebral and hip fractures. By contrast, there is very little information about calcium absorption in other types of postmenopausal fracture. We now report a series of 549 untreated, Caucasian postmenopausal women in whom we recorded prevalent fractures, measured radiocalcium absorption, and obtained radiographs of the lateral thoracic and lumbar spine. Of these women, 172 had no prevalent fractures, showed normal spine radiographs, and served as controls; 72 had one or more peripheral fractures but normal spine radiographs; 147 had one or more wedged or crushed vertebrae but no peripheral fractures; and 158 had a history of peripheral fracture and one or more fractured vertebrae. Age-adjusted radiocalcium absorption was significantly lower in the two groups with spinal fractures than in the controls ( P<0.001) but not in the group with peripheral fractures only. It was also lower in the cases with more than two spinal fractures than in those with two or less (P<0.001). In respect of peripheral fractures, the greatest age-adjusted absorption deficit was found in fractures of the humerus (35%) followed by hip (32%), spine (21%), wrist (19%), and rib 17% (all significant but not significantly different from each other). Lesser deficits in tibia, ankle and foot fractures were not significant but type 2 errors could not be excluded. We conclude that impaired calcium absorption is particularly associated with those fractures for which osteoporosis is a significant risk factor.

Transfer of alkaline earth elements in mothers' milk and doses from 45Ca, 90Sr and 226Ra.

An international programme of work is currently under way to develop methods for calculating doses to infants from ingestion of radionuclides present in mothers' milk. This paper considers the special case of the alkaline earth elements. Models have been developed for 45Ca, 90Sr and 226Ra and the sensitivity of results to various changes in parameter values is discussed. A complication when calculating doses from intakes of radium is that the International Commission on Radiological Protection has previously recommended that doses from decay products of radium should be calculated using element-specific biokinetic models (so-called independent biokinetics). An extension of this method to the models for breastfeeding is proposed. Preliminary estimates of the doses received by the infant for a number of maternal intake scenarios show that doses to the infant can exceed the corresponding adult dose, such as for 45Ca (ratio = 3.1) while, in other cases such as 90Sr, the infant dose can be a significant fraction of the adult dose.

A new view of K+ -induced contraction in rat aorta: the role of Ca2+ binding.

Strong, K+ -induced contractions of rat aorta in Ca-free, Mg-free media were not accompanied by increased intracellular calcium concentration, [Ca2+](i), whereas such contractions in the presence of the divalent cations were correlated with rising [Ca2+](i) as assessed by fura-2. At the same time, calcium channel blockers, a modulator of Ca2+-binding proteins, and a modulator of actin polymerization, inhibited all types of K+ -induced contractions. Increasing the K+ in isotonic medium evoked a rise of (45)Ca2+ binding to the plasma membrane of freshly isolated aortic cells. Although Ca2+ -dependent events underlie the mechanism of K+ -induced vascular contractions in both the presence and absence of Ca2+, in contrast to the view that [Ca2+](i) is a key regulator of excitation-contraction coupling in smooth muscle, we suggest that the modulation of Mg2+ -dependent Ca2+ binding, probably within/at the L-type calcium channel by K+, is a trigger for aortic contraction. This Ca2+ binding may then activate actin-myosin interaction.

Analysis of dose distribution for heavily exposed workers in the first criticality accident in Japan.

The first criticality accident in Japan occurred in a uranium processing plant in Tokai-mura on September 30, 1999. The accident, which occurred while a large amount of enriched uranyl nitrate solution was being loaded into a tank, led to a chain reaction that continued for 20 h. Two workers who were pouring the uranium solution into the tank at the time were heterogeneously exposed to neutrons and gamma rays produced by nuclear fission. Analysis of dose distributions was essential for the understanding of the clinical course observed in the skin and organs of these workers. We developed a numerical simulation system, which consists of mathematical human models and Monte Carlo radiation transport programs, for analyzing dose distributions in various postures and applied the system to the dose analysis for the two workers. This analysis revealed the extreme heterogeneity of the doses from neutrons and gamma rays in the skin and body, which depended on the positions and postures of the workers. The detailed dose analysis presented here using color maps is indispensable for an understanding of the biological effects of high-dose exposure to a mixed field of neutrons and gamma rays as well as for the development of emergency treatments for victims of radiation exposure.