Calciprotein Particles Link Disturbed Mineral Homeostasis with Cardiovascular Disease by Causing Endothelial Dysfunction and Vascular Inflammation.

An association between high serum calcium/phosphate and cardiovascular events or death is well-established. However, a mechanistic explanation of this correlation is lacking. Here, we examined the role of calciprotein particles (CPPs), nanoscale bodies forming in the human blood upon its supersaturation with calcium and phosphate, in cardiovascular disease. The serum of patients with coronary artery disease or cerebrovascular disease displayed an increased propensity to form CPPs in combination with elevated ionised calcium as well as reduced albumin levels, altogether indicative of reduced Ca2+-binding capacity. Intravenous administration of CPPs to normolipidemic and normotensive Wistar rats provoked intimal hyperplasia and adventitial/perivascular inflammation in both balloon-injured and intact aortas in the absence of other cardiovascular risk factors. Upon the addition to primary human arterial endothelial cells, CPPs induced lysosome-dependent cell death, promoted the release of pro-inflammatory cytokines, stimulated leukocyte adhesion, and triggered endothelial-to-mesenchymal transition. We concluded that CPPs, which are formed in the blood as a result of altered mineral homeostasis, cause endothelial dysfunction and vascular inflammation, thereby contributing to the development of cardiovascular disease.

Regional citrate anticoagulation in membrane based plasma exchange: Safety, efficacy and effect on calcium balance.

AIM: To assess the efficacy, safety and calcium balance of a membrane based regional citrate anticoagulation plasma exchange protocol. METHODS: This was an observational, prospective, single centre study of membrane separation plasma exchange using regional citrate anticoagulation. It was performed using a fixed dose pre-filter citrate infusion that was based on the plasma flow rate. Patients received a post filter calcium infusion that was modified during treatment based on systemic ionized calcium monitoring. Post filter ionized calcium was not assessed. Safety and efficacy were assessed by extraction of clinical events and laboratory data contemporaneously recorded in electronic health records. RESULTS: Thirty-six sessions in five patients were performed. No patients developed symptomatic hypocalcaemia, and no patient had a recorded ionized calcium below 0.81 mmol/L. Filter clotting occurred in two sessions. The mean net calcium gained was 9.6 ± 1.8 mmol per session. CONCLUSION: Regional citrate anticoagulated membrane separation plasma exchange can be performed safely and effectively without the need for post filter ionized calcium monitoring. The algorithm employed resulted in a net calcium gain.

Effects of oral calcium supplementation on mineral and acid-base status, energy metabolites, and health of postpartum dairy cows.

Two experiments were conducted to characterize blood concentrations of minerals and acid-base status after oral dosing of Ca salts and to determine the effects of oral Ca on mineral and metabolic status and incidence diseases. The hypotheses were that administration of oral Ca as CaCl2 and CaSO4 maintains blood total Ca (tCa) concentrations ≥2.125 mM and reduces the incidence of diseases in early lactation. In experiment 1, 18 Holstein cows on the day of calving were assigned to receive a single dose of 0, 43, or 86g of Ca as an oral bolus. Blood was sampled before and after treatments to characterize acid-base status and concentrations of minerals. In experiment 2, 450 Holstein cows considered of low (LRM; normal calving) or high risk (HRM; dystocia, twins, stillbirth, retained placenta, vulvo-vaginal laceration, or a combination of these) of metritis (primiparous-LRM=84; primiparous-HRM=84; multiparous-LRM=138; multiparous-HRM=138) on the day of calving were blocked by parity and then randomly assigned to control, no Ca supplementation; 86g of Ca on d 0 and 1 postpartum (CaS1); or 86g of Ca on d 0 and 1 postpartum followed by 43g/d on d 2 to 4 postpartum (CaS4). Blood was sampled before and 30 min after treatment on d 0, and 30 min after treatments on d 1 to 4, and d 7 and 10 for determination of concentrations of minerals and metabolites and blood acid-base responses. Disease incidence was evaluated for the first 30 DIM. Concentrations of ionized Ca (iCa) increased for 2h in cows supplemented with 43g of Ca and fewer than 8h in cows supplemented with 86g of Ca. The changes in iCa concentrations from pretreatment to 30 min after 86g of Ca supplemented on d 0 were 0.11±0.03 mM in multiparous cows and 0.25±0.03 mM in primiparous cows. Oral Ca reduced the incidence of subclinical hypocalcemia (SCH; tCa <2.125mM) in the first 4 d in the experiment (control=69.3%; CaS1=57.5%; CaS4=34.2%). Calcium supplementation decreased the prevalence of SCH on d 0 and 1 postpartum in all cows. Stopping oral Ca in CaS1 on d 1 postpartum, however, caused a rebound in SCH on d 2 to 4 postpartum in primiparous cows. Oral Ca increased the incidence of metritis (control=22.7%; CaS1=34.8%; CaS4=32.8%), primarily because of an increase in LRM primiparous cows (control=17.9%; CaS1=35.7%; CaS4=42.9%). Oral Ca increased morbidity in primiparous cows (control=38.1%; CaS1=61.8%; CaS4=60.3%) but had no effect on multiparous cows (control=38.2%; CaS1=35.1%; CaS4=30.1%). Large doses of oral Ca as salts of chloride and sulfate in the first days postpartum should be avoided in primiparous cows and used only in cows at risk of clinical hypocalcemia.

Comparison of Modified Impedance Whole Blood Platelet Aggregation Method Detecting Platelet Function in ACS Patients with Different CYP2C19 Genotypes.

BACKGROUND: A reliable laboratory test to monitor onclopidogrel platelet reactivity (PR) is very necessary. In addition, genetic factors also play an important part in onclopidogrel PR. This study aimed to modify the original impedance whole blood platelet aggregation assay associated with the release assay to monitor onclopidogrel PR and assess their relationship with genotype. METHODS: We adjusted the concentration of calcium in the in vitro reaction system of platelet aggregation to modify the original impedance whole blood platelet aggregation assay. Meanwhile, chronolume, which quantified the adenosine triphosphate (ATP) released from platelet dense granules, is added to this reaction system to reflect the platelet release function. In the modified assay, platelet magnified activation time (MAT) and the maximal platelet ATP release value (RV) were used to reflect platelet function parameters. In the original assay, the electrical resistance (omega) and RV were used to reflect platelet function parameters. Onclopidogrel PR was detected by the original impedance whole blood platelet aggregation assay, modified assay, and flow cytometric vasodilator stimulated phosphoprotein (VASP) assay in 168 patients with acute coronary syndromes (ACS). CYP2C19*2 and CYP2C19*3 polymorphisms were also detected in all of these patients. RESULTS: This modified method showed that when 12.5 microL CaCl2 (0.2 mmol/L) was added to the reaction system, MAT was appropriate (93 +/- 23 seconds). The CVs for the modified impedance assay and release assay were 9.31% and 6.13%, respectively. The mean VASP-PRI in the patient group treated with clopidogrel was significantly lower than that in the control group without antiplatelet therapy (54.88 +/- 16.81% vs. 79.86 +/- 10.24%, p < 0.001). MAT of the modified method in VASP PRI > 50% group were shorter than that in the PRI < 50% group [185 (154-241) vs. 214 (184-250), p < 0.051. Meanwhile, the RV of the modified method in VASP PRI > 50% group were higher than that in the PRI < 50% group [1.00 (0.72-1.47) vs. 0.82 (0.62-1.08), p < 0.051. However, the electrical resistance (omega) and RV of the original method showed no differences between the two groups [0 (0-2) vs. 0 (0-1.25), 0.05 (0-0.25) vs. 0.08 (0-0.24); p > 0.05, p > 0.05, respectively). Moreover, neither the original method nor the modified method showed differences in patients with CYP2C19 (*2 and *3) wild type and mutant type. CONCLUSIONS: The consistency of the modified assay and VASP assay is good. The modified assay may be a potentially good laboratory method to monitor antiplatelet therapy.

The effect of co-administration of intravenous calcium chloride and oxytocin on maternal hemodynamics and uterine tone following cesarean delivery: a double-blinded, randomized, placebo-controlled trial.

BACKGROUND: Oxytocin administration to prevent uterine atony following cesarean delivery is associated with adverse effects including hypotension, tachycardia, and nausea. Calcium chloride increases mean arterial pressure, systemic vascular resistance, and uterine smooth muscle contractility. This study evaluated whether the co-administration of calcium chloride with oxytocin following cesarean delivery could alter maternal hemodynamics. Secondary outcomes included uterine tone and blood loss. METHODS: Sixty healthy parturients with singleton, term, vertex pregnancies undergoing elective cesarean delivery under spinal anesthesia were randomized to one of three study solutions given intravenously immediately after umbilical cord clamping: (1) placebo, oxytocin 5U alone; (2) CA-200, oxytocin 5U+calcium chloride 200mg; or (3) CA-400, oxytocin 5U+calcium chloride 400mg. Blood pressure, heart rate, uterine tone, vasopressor or alternate uterotonic use and the incidence of nausea or vomiting were recorded. Baseline and intraoperative plasma concentration of ionized calcium and hematocrit were measured. RESULTS: Plasma concentration of ionized calcium was elevated in both study groups compared with placebo (P=0.001). Blood pressure decreased and heart rate increased in all groups (P <0.0001), with no differences between groups. No differences were observed between groups in uterine tone, vasopressor use, hematocrit change, estimated blood loss, incision-to-delivery interval, delivery-to-skin closure interval, total intravenous fluid administered or incidence of nausea. CONCLUSIONS: The decrease in blood pressure associated with oxytocin administration following cesarean delivery was not attenuated with co-administration of calcium chloride at the doses evaluated. Vasopressor use, uterine tone, and blood loss were also unaffected.

Management of fluoride induced testicular disorders by calcium and vitamin-E co-administration in the albino rat.

Fluoride contamination of drinking water can disrupt male gametogenesis and steroidogenesis and induce testicular oxidative stress. Treatment of rats with sodium fluoride at the dose of 20 mg/kg/day for 28 days resulted in significant diminution of testicular Delta5,3beta-hydroxysteroid dehydrogenase (HSD) and 17beta-hydroxysteroid dehydrogenase (HSD) activities and low plasma levels of testosterone, follicular stimulating hormone (FSH) and leutinizing hormone (LH). Spermatogenesis inhibited after sodium fluoride treatment has been assessed here by the quantification of different generation of germ cells like spermatogonia A (ASg), preleptotene spermatocyte (PLSc), midpachytene spermatocyte (MPSc) and step 7 spermatid (7Sd) at stage VII of seminiferous epithelial cycle. Furthermore, fluoride treatment was associated with low activities of testicular, prostatic and epididymal catalase (CAT), superoxide dismutase (SOD) and peroxidase along with elevation of malondialdehyde (MDA) and conjugated dienes (CD) in those tissues. Co-administration of calcium and Vitamin-E with fluoride resulted in a significant recovery from testicular disorders and oxidative stress in the testis and male accessory sex organs. The results of this study demonstrate that fluoride exposure, at the dose available in drinking water in contaminated areas, led to inhibition of testicular gametogenesis and steroidogenesis in association with oxidative stress in the testis and male accessory sex organs, which are protected significantly by dietary agents like Vitamin-E and calcium.

Manipulation of calciumhomeostatic mechanisms in man: what are the possibilities?

The aim of our studies on parathyroid hormone dynamics were to establish standardized methods for induction of hypocalcaemia, sequential hypercalcaemia and normocalcaemia and sequential hypocalcaemia and hypercalcaemia suitable for careful and detailed evaluation of the PTH(1-84) secretion in vivo. We found that at least two distinctly different mechanisms of PTH(1-84) secretion serve to protect normal humans against hypo- and hypercalcaemia. First, an initial decrement of B-Ca2+ leads to a large transient release of preformed PTH(1-84) from the cellular depots, whereas, an initial increment of B-Ca2+ leads to almost immediate suppression of PTH(1-84) release. The change in PTH(1-84) release is rate dependent in either direction and demonstrable even at small decrements or increments of B-Ca2+. This mechanism of delta regulation provide a strong homeostatic mechanism for maintaining a stable extracellular calcium level during slow as well as rapid changes in B-Ca2+. Second, a mechanism of steady state regulation for continued secretion takes over, being dependent on the absolute B-Ca2+ concentration, which probably controls the synthesis of PTH(1-84) molecules. Selective investigation of the steady state response to hypocalcaemia demands elimination of preformed PTH(1-84). With this precaution, we described the inverse sigmoidal relationship in vivo between the steady state pairs of B-Ca2+ and S-PTH(1-84) in normal humans. The calcium set-points of Brown measured by this computer method were significantly lower than Parfitt's calcium set-points in normal humans, but strikingly well correlated. This observation supporting the view that Brown and Parfitt describe two different points on the same sigmoidal curve, corresponding to 50% and about 85% inhibition of PTH(1-84) in normal humans.

Development of a novel concept (Calcigard) for activation of calcium absorption capacity and prevention of milk fever.

The background to the development of a novel concept for the prepartal activation of calcium absorption capacity as a means of preventing parturient hypocalcaemia and milk fever in grazing ruminants is described. It was hypothesised that this objective could be achieved by decreasing the bio-availability of calcium from pasture for a 3 week period. Soya bean oil was chosen as a supplement, from a number of potential binding agents, to form poorly digestible calcium soaps in the gastrointestinal tract. 28 mature twin-pregnant ewes in late pregnancy were used as assay animals to test the hypothesis, and they proved to be a sensitive experimental model for dairy cows. Following the treatment period, overnight starvation was used to challenge calcium homeostasis. Calcium absorption capacity was assessed indirectly by measuring strontium concentrations in plasma following oral dosing with strontium chloride. Strong support for the hypothesis was obtained as the 14 Treated ewes were protected from severe fasting-induced hypocalcaemia (P = 0.002), and this was associated with a greatly increased capacity of the ewes to absorb calcium. The feeding strategy developed in this experiment led to the production of a Calcigard concentrate supplement which was subsequently shown to protect cows from hypocalcaemia and milk fever, and stimulate production.

Experimental hypocalcemia induced by hemodialysis in goats.

To evaluate whether hemodialysis with a dialysate containing no calcium (Ca-free HD) can induce hypocalcemia and restore the clinical signs and blood biochemical changes in naturally occurred hypocalcemic disorder in ruminants, the clinical signs and the changes in plasma electrolytes and minerals concentrations were observed in goats during 6-hr hemodialysis. The four goats received hemodialysis with the dialysate containing calcium (Ca HD), and 10 days later they had Ca-free HD. The plasma ionized Ca (Ca++) and total Ca (TCa) concentrations were not affected by Ca HD, whereas the levels significantly decreased during whole period of Ca-free HD. The Ca++ and TCa concentrations were 0.69+/-0.06 mmol/l and 5.9+/-0.3 mg/dl at 6 hr of Ca-free HD, respectively. The clinical signs observed during Ca-free HD seemed to resemble to those in naturally occurred hypocalcemic cases that were reported previously. Therefore, Ca-free HD was suggested to be one of the possible methods to induce experimental hypocalcemia in ruminants.

Calcium speciation and exchange between blood and extrapallial fluid of the quahog Mercenaria mercenaria (L.).

Calcium and small organic molecules (e.g., tyrosine, MW 181 Da) introduced into the extrapallial fluid (EPF) of the quahog Mercenaria mercenaria exhibit rapid fluxes across the outer mantle epithelium and are distributed throughout the circulatory system within 3 h. Larger molecules (e.g., bovine serum albumin, MW 66,000 Da) are less readily exchanged between EPF and blood. The protein compositions of blood plasma and EPF are different, with at least seven protein bands expressed more prominently in the EPF. Equilibrium dialysis experiments reveal that Ca2+ constitutes only 2% of the total Ca in plasma; most of the Ca (85%) is bound to macromolecules, and the remaining 13% is present as dialyzable low molecular weight moieties. This distribution cannot be explained by speciation of inorganic Ca alone, since the MINTEQA2 equilibrium speciation model predicts that 79%-86% of the Ca should be present as Ca2+, with the remainder as CaSO4 (20%-13%). However, inclusion of a weakly Ca-binding organic molecule (log10 Ka approximately 2 M-1) into MINTEQA2 could fully reconcile modeling with experimental measurements. Results suggest that calcium transport in blood plasma and EPF is mediated by a suite of proteins and small organic ligands with a low affinity for Ca.

Laboratory diagnosis of APC-resistance: a critical evaluation of the test and the development of diagnostic criteria.

The APC-resistance test consists of two APTT's, one in the presence and one in the absence of a fixed amount of Activated Protein C (APC), and is a simple and reliable method to detect a reduced sensitivity to the anticoagulant action of APC (APC-resistance). At a fixed concentration of APC the prolongation of the APTT is dependent on the activator, the CaCl2 concentration, the citrate concentration in the sample, and on sample handling. The effect of sample handling can be reduced by calculating the APC-Sensitivity Ratio (APC-SR). The actual prolongation of the APTT is also influenced by low protein S levels (reduction of APC-SR) and by reduced levels of factors V, VIII and IX (increase of APC-SR). The APC-SR is most dramatically effected by reduced levels of factors II and X, which result often in "unmeasurable" APC-SR's in plasmas of patients on oral anticoagulant treatment. So at present no reliable APC-SR's can be measured in these patients. Patients treated with heparin can be tested after treatment of their plasma with Hepzym. The inter- and intra-assay variation in the APC-SR is 4% and 2%, respectively, when using the same batches of activator and APC. The variation which is introduced in the APC-SR by use of different batches of activator or APC, or by the use of different APC or CaCl2 concentrations, can effectively be avoided by expressing the result of the test in normalized-APC-SR (n-APC-SR).(ABSTRACT TRUNCATED AT 250 WORDS)

Dose response dependency in regulation of acute PTH (1-84) release and suppression in normal humans: a citrate and calcium infusion study.

The aim of the present study was to investigate the possible dose response dependency of the very early changes in intact parathyroid hormone concentrations (PTH) on different rates of blood ionized calcium (B-Ca2+) lowering and raising. On 8 different days, four healthy volunteers received trisodium-citrate infusions at five different rates and calcium chloride infusions at three different rates, all of 10 min duration. S-PTH and B-Ca2+ were measured twice before each infusion and after 1, 2, 3, 4, 5, 7, and 10 min of infusion. The decrements of B-Ca2+ expressed as area under the curve (AUC) correlated with the rate of trisodium-citrate infusions (r = 0.97, p < 0.001) and furthermore, these B-Ca2+ decrements were matched by S-PTH increments expressed as AUC (r = 0.96, p < 0001). Multigroup comparisons on the results of protocol A showed statistical significant (p < 0.02). The increments of B-Ca2+ expressed as AUC correlated with the rate of calcium chloride infusions (r = 0.92, p < 0.001) and furthermore, these B-Ca2+ increments were matched by S-PTH decrements measured as AUC (r = 0.95, p > 0.001). Multigroup comparisons on the results of protocol B showed statistical significant (p < 0.05). In conclusion, acute B-Ca2+ lowering and raising at different rates promotes stimulation and inhibition of the acute PTH release in rate dependent manner. For this mechanism being distinctly different from the steady state control of PTH secretion, we suggest the term 'delta regulation' (delta, i.e. the sign for change).

Does calcium chloride help restore maternal blood pressure and uterine blood flow during hemorrhagic hypotension in hypermagnesemic gravid ewes?

Magnesium sulfate worsens maternal hypotension and fetal oxygenation during hemorrhage in gravid ewes. The purpose of this study was to determine whether calcium chloride administration is a useful adjunct to blood transfusion during hemorrhagic hypotension in hypermagnesemic gravid ewes. Sixteen experiments were performed in eight chronically instrumented animals between 0.8 and 0.9 of timed gestation. The experimental sequence included (a) T = 0: magnesium sulfate 4 g IV; (b) T = 5: infusion of magnesium sulfate 4 g/h IV; (c) T = 90: maternal hemorrhage 20 mL/kg over 55 min; (d) T = 147: calcium chloride 10 mg/kg or normal saline (NS-control) 0.1 mL/kg IV; (e) T = 160: transfusion of collected maternal blood over 55 min. Magnesium sulfate alone slightly decreased maternal mean arterial pressure (P = 0.002) and increased uterine blood flow (P = 0.0001) in both groups before hemorrhage. During hemorrhage, maternal mean arterial pressure, cardiac output, and uterine blood flow, and fetal PO2 and pH all decreased sharply (P = 0.0001). Cardiac output increased (P = 0.0005) modestly just after the intravenous bolus of calcium chloride. Maternal mean arterial pressure was significantly higher (P = 0.03) during transfusion in the calcium chloride group than in the NS-control group, but only after mean arterial pressure was near baseline measurements. Maternal uterine blood flow and fetal PO2 and pH responses over time were similar in the two groups. We conclude that intravenous administration of calcium chloride (10 mg/kg) transiently increased cardiac output during hemorrhagic hypotension and slightly increased mean arterial pressure during transfusion in hypermagnesemic gravid ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipase C mediated inhibition of factor VII requires triglyceride-rich lipoproteins.

The reduction of plasma factor VII (FVII) activity by phospholipase C (PLC), in vitro, has been proposed as a possible indication of a risk of cardiovascular disease. The ability of PLC to reduce FVII activity was found to require calcium ions and the presence of triglyceride-rich lipoproteins (e.g. chylomicra and very-low density lipoproteins) rather than high or low density lipoproteins. The PLC-mediated reduction of FVII activity was prevented by pre-incubation of PLC with chylomicra, before adding FVII, and this suggests that PLC may act on triglyceride-rich lipoproteins already bound to FVII in order to reduce FVII activity. At optimal PLC concentration, the extent of the reduction in FVII activity was proportional to the concentration of chylomicra. The detergent, Tween, prevented any loss of FVII activity, in both plasma and purified systems, if it was present at the beginning of the incubation with PLC. Addition of Tween, but not EDTA, after inhibition of FVII activity had occurred, caused a partial restoration of FVII activity. It is concluded that PLC reduces FVII activity by modifying triglyceride-rich lipoproteins to a form which binds to FVII, independently of calcium ions, and which inhibits procoagulant activity. The detection of PLC-sensitive procoagulant activity. The detection of PLC-sensitive FVII activity may therefore have no greater significance than the measurement of plasma triglyceride levels in predicting a risk of cardiovascular disease.

Influence of calcium infusion on plasma atrial natriuretic peptide in conscious dogs: intervention with calcium antagonist, verapamil.

In studies in conscious dogs, 1 liter 0.3% calcium chloride infusion resulted in a 163% increase in serum ionized calcium (iCa2+), 166% increase in plasma immunoreactive atrial natriuretic peptide (irANP) and 33% increase in mean blood pressure with significant positive correlation between serum iCa2+ and plasma irANP levels. Pretreatment with verapamil reversed the effects of calcium infusion. These studies have demonstrated that calcium ions play an important role in ANP secretion with reversal by calcium antagonist, verapamil. Hyponatremia seen with calcium infusion could reflect calcium-enhanced sodium excretion. Hypercalcemia was accompanied by non-significant changes in plasma renin activity and significantly elevated serum aldosterone not reversed by verapamil.

Calcium administration increases the mortality of endotoxic shock in rats.

Calcium chloride is administered frequently to critically ill patients to improve cardiac output and BP. However, Ca has been implicated in the pathophysiology of shock and ischemic disorders. To test the hypothesis that Ca may be deleterious to shock outcome, we studied the effects of CaCl and Ca chelator (EGTA) infusions on mean arterial pressure (MAP) responses to endotoxin and 24-h survival in rats. Increasing ionized Ca from 4.1 +/- 0.06 to 4.9 +/- 0.20 and 8.5 +/- 0.52 mg/dl progressively increased endotoxin lethality from 20% to 37% and 80%, respectively. This occurred despite slight improvements in MAP in hypercalcemic rats. Conversely, hypocalcemia (3.6 +/- 0.08 mg/dl) lowered endotoxin-induced mortality to 0 without significant effects on MAP. Ca and EGTA infusions alone were not associated with any mortality. Although Ca administration may improve MAP, it significantly increases mortality associated with endotoxic shock in rats. Based on these observations, we advise caution when using Ca in patients with sepsis.

Cardiogenic shock associated with calcium-channel and beta blockers: reversal with intravenous calcium chloride.

Two cases in which oral ingestion of beta blocker and slow calcium-channel blocker was associated with profound hypotension and bradycardia are reported, including one case in which serum levels of both drugs were documented in the normal range at a time of severe clinical toxicity. Though unresponsive to usual therapeutic interventions, both patients showed an immediate and dramatic response to intravenous calcium chloride. It is recommended that intravenous calcium chloride be considered in any patient using routine doses of these two agents who presents with hypotension and/or bradycardia.

Choice of calcium salt. A comparison of the effects of calcium chloride and gluconate on plasma ionized calcium.

Equimolar quantities of calcium chloride and calcium gluconate produced similar changes in plasma ionised calcium concentration when injected intravenously into anaesthetised ferrets or when added to human blood in vitro. In vivo changes were followed with a calcium electrode positioned in the animal's aorta, and this showed that the ionisation of calcium gluconate on its first pass through the circulation is as great as that of calcium chloride. This does not support the common suggestion that calcium chloride is preferable to calcium gluconate because of its greater ionisation.