Type 1 innate lymphoid cells regulate the onset of Toxoplasma gondii-induced neuroinflammation

Cerebral infections are restrained by a complex interplay of tissue-resident and recruited peripheral immune cells. Whether innate lymphoid cells (ILCs) are involved in the orchestration of the neuroinflammatory dynamics is not fully understood. Here, we demonstrate that ILCs accumulate in the cerebral parenchyma, the choroid plexus, and the meninges in the onset of cerebral Toxoplasma gondii infection. Antibody-mediated depletion of conventional natural killer (cNK) cells and ILC1s in the early stage of infection results in diminished cytokine and chemokine expression and increased cerebral parasite burden. Using cNK- and ILC1-deficient murine models, we demonstrate that exclusively the lack of ILC1s affects cerebral immune responses. In summary, our results provide evidence that ILC1s are an early source of IFN-γ and TNF in response to cerebral T. gondii infection, thereby inducing host defense factors and initiating the development of a neuroinflammatory response.

Serum-ionised magnesium in patients with acute myocardial infarction. Relation to cardiac arrhythmias, left ventricular function and mortality

Measurement of serum-ionised magnesium has recently become available, and we report the first study of the relation of this parameter to arrhythmias, left ventricular function and mortality in patients with an acute myocardial infarction. Serum-ionised magnesium was determined in 217 consecutive patients admitted to hospital with an enzyme confirmed AMI. 70 healthy subjects acted as a control group. The main study parameters were occurrence of arrhythmias, left ventricular function estimated by echocardiography, and mortality after 10 months for the AMI patients. AMI patients had significantly lower serum-ionised magnesium compared to healthy controls but the level of serum-ionised magnesium in the acute phase of a MI was neither related to arrhythmias, left ventricular function nor mortality.

Lack of relationship between serum and gallbladder bile calcium in patients with gallstone disease

BACKGROUND

Recent studies suggest that alternation in serum calcium influences the level of gallbladder bile ionized calcium (Ca2+). Theoretically, this could increase the risk of calcium precipitation in the gallbladder.

METHODS

We therefore measured serum and gallbladder bile minerals in patients with gallstones (n = 27) and without (n = 10, controls). The serum samples were taken just prior to induction of anaesthesia and gallbladder bile was aspirated before any manipulation of the gallbladder.

RESULTS

The active molality of Ca2+ in gallbladder bile was not statistically significant different between cases and controls (0.44 +/- 0.16 vs. 0.40 +/- 0.10 mmol/kg), whereas pH was significantly lower (6.94 +/- 0.31 vs. 7.36 +/- 0.28, p < 0.0001) and cholesterol higher (4.37 +/- 2.70 vs. 1.79 +/- 1.33 mmol/l; p < 0.01) in gallbladder bile obtained from cases. Serum Ca2+ at actual pH, magnesium and phosphate were significantly higher among cases than in controls. Gallbladder bile active molality of Ca2+ was significantly correlated with bile total calcium in both groups (r = 0.72; p < 0.001 and r = 0.91; p < 0.001, respectively). In controls only, we observed a positive relationship between serum Ca2+ at actual pH and the active molality of Ca2+ in bile (r = 0.61; p < 0.05).

CONCLUSION

Our study demonstrates that Ca2+ in gallbladder bile does not differ between cases and controls. The lack of correlation between serum and gallbladder bile constituents in cases compared to controls suggests that changes in calcium equilibration between bile and serum in patients with gallstone disease might be of importance for the formation of gallstones.

Evaluation of an ionized magnesium-pH analyzer--NOVA 8

An ion-selective analyzer (NOVA 8 [previously NOVA CRT], NOVA Biomedical Waltham, USA) for simultaneous measurement of the concentration of ionized magnesium (cMG2+) and pH is investigated for linearity and influence of calcium ions on the Mg2+ results in different Mg2+ aqueous solutions with/without added calcium. Within the cMg2+ range 0-3.0 mmol/L, which covers most clinical values, we found cMg2+ values close to the line of identity, with a sensitivity about 94%, but 0.09 mmol/L lower in the absence of Ca2+. The analytical precision (CV) for human serum control was 1.7% in the physiological range. The accuracy and precision data for the Mg2+ electrode meet the demands for reliable results within the range for clinical use. We found a reference interval (95%) for cMg2+ of between 0.43 and 0.59 mmol/L serum, with a mean value of 0.51 mmol/L for healthy adults in the non-fasting state with no relation to sex or age. The mean cMg2+ was 61% of the mean concentration of plasma total magnesium (cTMg) ranging from (95%) 49% to 73%. No significant correlation was found between cMg2+ and total protein, albumin, phosphate, Ca2+, and total CO2. No significant difference was found between mean values for cMg2+ in whole blood, plasma, and serum. Serum samples could be stored for 24 h at 4 degrees C without significant change. Storage at -20 degrees C for 7 months caused a mean cMg2+ decrease of 8.3%. The mean slope delta lgcMg2+/delta pH measured after equilibration with different pCO2 values in each serum sample from the reference population was -0.0110, indicating a close agreement between the values for actual cMg2+ and adjusted cMg2+ (pH = 7.4).

[Osteoporosis-profile--a bad examination?]

A so-called osteoporosis-profile has become increasingly popular among Danish doctors. Future bone loss in peri- and postmenopausal women is estimated by means of an algorithm comprising serum osteocalcin and alkaline phosphatases as markers of bone formation and urinary calcium and hydroxyproline excretions, corrected for creatinine, as markers of bone resorption. The osteoporosis-profile, performed by Medi-Lab, was tested in six females aged 46-56 years. Three different diets were used on three successive week-ends, each ending with a collagen-free supper and an overnight fast. Individual changes in estimated bone loss of up to 200-300% were found, demonstrating that the test was useless in a single person.

Childhood sarcoidosis presenting with hypercalcaemic crisis

We report a case of hypercalcaemic crisis due to sarcoidosis in a 15-year-old boy. The clinical suspicion of sarcoidosis was confirmed by a liver biopsy. At admission serum calcium, 1,25(OH)2 and ACE were elevated and iPTH was suppressed. The levels of serum total and ionized calcium, iPTH, ACE, 1,25(OH)2 and 25-OH were followed and chest X-ray and pulmonary function tests were performed during systemic steroid treatment. The clinical condition improved during treatment and the paraclinical measurements normalised within 5 weeks. The mechanism whereby hypercalcaemia occurs in childhood sarcoidosis is clarified.

Serum ionized calcium, parathyroid hormone and phosphate in uremic patients during and between hemodialysis

The serum concentrations of actual ionized calcium (at actual pH), adjusted ionized calcium (at pH 7.4), pH, intact parathyroid hormone (PTH) and phosphate were studied in ten patients during and between two hemodialysis sessions using a dialysate containing 1.66 mmol/l of calcium. Actual ionized calcium and adjusted ionized calcium increased during hemodialysis from 1.19 to 1.38 and 1.43 mmol/l, respectively (mean values) and returned to predialysis values within five and nine hours postdialysis. Serum PTH decreased from 165 ng/l to 55 ng/l (median values) during hemodialysis but two-hour postdialysis the level did not differ significantly from the predialysis level. Serum phosphate decreased from 2.05 mmol/l to 1.11 mmol/l during hemodialysis, and increased slowly towards the predialysis level. The level of pH increased from 7.40 to 7.47 during hemodialysis and reached predialysis level after nine hours. In a multivariate analysis including actual and adjusted ionized calcium, pH, phosphate and PTH, only actual or adjusted ionized calcium was associated with the level of PTH. We conclude that the effect of dialysate calcium on the levels of ionized calcium and PTH is of very short duration postdialysis.

Effects of age, sex, season and diet on serum ionized calcium, parathyroid hormone and vitamin D in a random population

OBJECTIVES

To study the influence of age, sex, season and diet on calcium status in normal subjects.

DESIGN

A random population study. Setting. Institutional clinic for large population studies.

SUBJECTS

The subjects were drawn randomly from the Danish Civil Registration System and represented a random sample of the background population in the area. The sample comprised 127 subjects (54 men and 73 women, aged 35-65 years).

MAIN OUTCOME MEASURES

The effects of age, sex, season and diet on parathyroid hormone (PTH),1,25-dihydroxyvitamin D (1,25(OH)2D) and 25-hydroxyvitamin D (25-OHD).

RESULTS

There was no statistical significant difference for the serum concentrations of ionized calcium, PTH, 1,25(OH)2D and 25-OHD between the two sexes, nor any influence by age in either sex, in contrast to serum phosphate, which declined significantly in men (P < 0.05), but tended to increase in women. Serum PTH (P < 0.009) showed seasonal fluctuations, whereas serum concentrations of 1,25(OH)2D, 25-OHD, ionized calcium, phosphate and magnesium remained stable throughout the year. Dietary intake of calcium and vitamin D were not related to any serum variables.

CONCLUSIONS

In healthy subjects differences between the two sexes exist regarding phosphate metabolism. Serum PTH shows seasonal fluctuations.

Calcium, magnesium, and free fatty acids in the formation of gallstones: a nested case-control study

In a nested case-control study, calcium status was assessed by measurements of serum total calcium, magnesium, phosphate, ionized calcium, parathyroid hormone, albumin, total CO2 (bicarbonate), and free fatty acids in relation to gallstone formation. The subjects were recruited from a cohort study (n = 4,581) on the epidemiology of gallstones in Denmark. The cohort was examined with ultrasonography twice, in 1983 and 1988; 63 subjects developed gallstones, and among those who did not, 122 were randomly selected as controls. Subjects with gallstones had significantly increased serum concentrations of total calcium, magnesium, and bicarbonate as compared with normal subjects. The difference was only observed in women. Age, body mass index, alcohol consumption, and smoking did not influence the results when included as covariables in a logistic regression analysis. Multivariate analysis showed increased concentrations of magnesium, bicarbonate, and parathyroid hormone to be significantly associated with gallstone disease in women. No significant association was observed between gallstone disease and serum variables in men.

Increased activity of ionised calcium in gall bladder bile in gall stone disease

The actual activity of ionised calcium (Ca2+) in gall bladder bile determined with an ion-selective electrode was significantly higher in patients with gall stone disease (n = 15) than in patients without gall stones (n = 10) (0.43 mmol/kg v 0.31 mmol/kg; p < 0.05). No change in the Ca2+ activity in any of the gall bladder bile samples was observed during equilibration with CO2. During titration with HCl/NaOH, however, the Ca2+ activity fell with increasing pH in a biphasic manner, with the breaking point occurring at a significantly lower median pH in patients with gall stones than in patients without (pH 7.1 v 8.2; p < 0.0001). The combination of a higher activity of calcium in bile and precipitation of bile salts taking place at a lower pH in patients with gall stone disease than in patients without gall stones suggests a major role for calcium and pH in the pathogenesis of gall stones. Strict anaerobic sampling is not necessary for the measurements of Ca2+ in gall bladder bile, because the Ca2+ was not significantly affected by the changes in pCO2. The metabolic studies suggest, however, that simultaneous measurements of the activity of Ca2+ and pH is important in order to interpret data for the calcium activity in gall bladder bile.

Performance characteristics of creatine kinase-MB isoenzyme measured with an immunoenzymometric and an immunoinhibition assay in acute myocardial infarction with and without thrombolytic therapy

In a time study we compared the analytical and clinical performance of the Tandem Icon QSR CK-MB enzyme-immunoassay (Hybritech) (creatine kinase-MB) and a creatine kinase-MB immunoinhibition method (Boehringer Mannheim GmbH) (creatine kinase-B). Two hundred and ninety-nine serum samples from 38 patients suspected of acute myocardial infarction were collected at regular intervals during 48 hours. Twenty-nine patients were diagnosed as having acute myocardial infarction, of whom 19 received thrombolytic therapy. Although highly correlated, the large scatter around the regression line at low values indicated a different clinical performance of the two methods. We evaluated and compared test performance at different decision levels by means of frequency distributions and predictive values of positive and negative results. For early diagnosis of acute myocardial infarction (4 hours after onset of pain) the Hybritech creatine kinase-MB method gives acceptable predictive values. In thrombolytic treated acute myocardial infarction patients, the peak creatine kinase-MB and creatine kinase-B concentrations were reached after 13.0 h and 13.6 h after the onset of pain, compared with 19.8 h and 17.8 h for patients without thrombolytic therapy.

Direct reading glucose electrodes detect the molality of glucose in plasma and whole blood

It is the activity that determines the direction of chemical processes, transport, etc. and thus provides the clinically more relevant information. Direct reading glucose electrodes consume glucose at a rate proportional to the glucose activity in the sample. The activity equals the molality (mmol glucose per kg water), so results from direct reading glucose electrodes must differ from the conventionally measured glucose concentration. This was observed in 159 whole blood samples which gave higher results from a direct reading glucose electrode than by our conventional method (y = 1.21x - 0.37 mmol/l). However, adjustment for the different water concentration due to salt, plasma proteins, and hemoglobin occupying space, gave results equal to the concentrations (y = 1.00x - 0.28 mmol/l, r = 0.997). Furthermore, results for samples with constant glucose concentration and varying albumin concentration correlated with the albumin concentration (r = 0.989), but not after adjustment for water concentration (r = 0.037, n.s.).

Adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood compared for clinical evaluation of patients with disorders of calcium metabolism

We report results for adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood from 183 patients with disorders of calcium metabolism (primary hyperparathyroidism, secondary hyperparathyroidism of malabsorption, primary hypoparathyroidism, Paget's disease, acromegaly, hypercalcemia of malignancy, osteoporosis, sarcoidosis, idiopathic hypercalciuria, and familial hypocalciuric hypercalcemia). The correlation and the equation for the linear regression between adjusted ionized calcium (y) and actual ionized calcium (x) were y = 1.011x + 0.005 mmol/L, r = 0.992, Sy,x = 0.021 mmol/L. Results were similar within each diagnostic group. Consistent agreement between adjusted and ionized calcium was observed in 96.7% of patients representing a variety of the most frequently encountered disorders of calcium metabolism. Thus we find adjusted ionized calcium to be as useful as actual ionized calcium for evaluation of patients with such disorders. Adjusted ionized calcium may therefore also be a logical choice for establishing agreement between laboratories for reference intervals in healthy adults.

Adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood compared for clinical evaluation of patients with disorders of calcium metabolism

We report results for adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood from 183 patients with disorders of calcium metabolism (primary hyperparathyroidism, secondary hyperparathyroidism of malabsorption, primary hypoparathyroidism, Paget's disease, acromegaly, hypercalcemia of malignancy, osteoporosis, sarcoidosis, idiopathic hypercalciuria, and familial hypocalciuric hypercalcemia). The correlation and the equation for the linear regression between adjusted ionized calcium (y) and actual ionized calcium (x) were y = 1.011x + 0.005 mmol/L, r = 0.992, Sy,x = 0.021 mmol/L. Results were similar within each diagnostic group. Consistent agreement between adjusted and ionized calcium was observed in 96.7% of patients representing a variety of the most frequently encountered disorders of calcium metabolism. Thus we find adjusted ionized calcium to be as useful as actual ionized calcium for evaluation of patients with such disorders. Adjusted ionized calcium may therefore also be a logical choice for establishing agreement between laboratories for reference intervals in healthy adults.

[Ionized calcium, total calcium and albumin corrected calcium in the serum in 1213 patients with suspected calcium metabolic diseases. A prospective multicenter study]

The correlation between serum ionized calcium, serum total calcium and albumin corrected total calcium was investigated in a prospective multicentre investigation of 1,213 patients with suspected calcium metabolic disease. 31.0% of the patients were misclassified when serum total calcium was measured instead of serum ionized calcium. The diagnostic discrepancy between the two methods decreased with the calculation of albumin corrected total calcium or calculated ionized calcium (17.9%). On justing for the analytical error connected with the measurement of ionized calcium, 11.2% of the patients were still misclassified. It is not possible precisely to predict serum ionized calcium from the measurement of serum total calcium and we recommend measurement of serum ionized calcium in patients believed to have calcium metabolic disease.

Palmitic acid stimulates glucose incorporation in the adipocyte by a mechanism likely involving intracellular calcium

The effect of palmitic acid on basal and insulin-stimulated incorporation of glucose into rat adipocytes was studied. Palmitic acid (2.40 mM) stimulated basal as well as insulin-stimulated glucose incorporation in rat adipocytes three and twofold, respectively. Similar degrees of stimulation of basal glucose oxidation by palmitate were also observed. The ability of palmitic acid to stimulate glucose uptake was additive with respect to the stimulation induced by insulin and was proportional to the palmitic acid concentration between 0.15 mM and 2.40 mM. Stimulation of glucose incorporation by palmitic acid was inhibited by preincubating the cells with quin2-AM, which accumulates intracellularly yielding the trapped chelator form. quin2, which binds intracellular Ca2+.The concentration of quin2-AM required for half-maximal inhibition of palmitic acid stimulated glucose incorporation was 3.8 +/- 1.2 microM (mean +/- SEM). The inhibition of palmitic acid-stimulated glucose incorporation by quin2-AM (10 microM) was overcome by incubating cells with the Ca2+ ionophore, A23187, in the presence of extracellular Ca2+ (2.6 mM). Chelation of extracellular Ca2+ with EGTA did not significantly affect the magnitude of palmitic acid-stimulated glucose incorporation. Dantrolene (12.5-100 microM) failed to affect basal or palmitic acid-stimulated glucose incorporation. These findings suggest that palmitic acid stimulates incorporation of glucose in the adipocyte by a mechanism dependent upon intracellular but not extracellular Ca2+.

Comparison of serum total calcium, albumin-corrected total calcium, and ionized calcium in 1213 patients with suspected calcium disorders

The correlations between serum ionized calcium, serum total calcium, total calcium corrected for albumin and calculated ionized calcium were investigated in a prospective multicentre investigation of 1213 patients suspected of having calcium metabolic disease. Diagnostic discordance between serum total calcium and measured ionized calcium was found in 31% of the patients. With the calculation of albumin-corrected total calcium or calculated ionized calcium the discordance decreased to 17.9%. The diagnostic discordance which could be ascribed to the analytical imprecision (CV = 1.5%) amounted to only 6.7%. Although we found highly significant correlations between the parameters, a considerable scatter around the regression line made prediction of ionized calcium from albumin-corrected total calcium unreliable in many patients.

Six direct radioimmunoassays of estradiol evaluated

We evaluated the analytical performance of six commercial direct radioimmunoassays of 17 beta-estradiol, those from Radioassay Systems Laboratories, IRE Medgenix, Biotecx Laboratories, Farmos Spectria, International CIS, and Diagnostic Products Corp. The mean value for estradiol (E2) and the within- and between-run CVs were determined for serum pools and control materials, measured in seven to 10 runs with each method. Mean values for E2 in pooled sera deviated by 75% to 350% from the means measured with our routinely used extraction method. Between-run CVs ranged from 4% to 14% for the direct assays as compared with 10% for the extraction assay. We also investigated, for two of the direct assays, the effect of extraction with diethyl ether before radioimmunoassay, with respect to improvement in the agreement with our extraction method. All of the assays were easy to perform and results were obtained within 4-5 h, but we conclude that matrix effects may be expected in direct assays of estradiol.

Six direct radioimmunoassays of estradiol evaluated

We evaluated the analytical performance of six commercial direct radioimmunoassays of 17 beta-estradiol, those from Radioassay Systems Laboratories, IRE Medgenix, Biotecx Laboratories, Farmos Spectria, International CIS, and Diagnostic Products Corp. The mean value for estradiol (E2) and the within- and between-run CVs were determined for serum pools and control materials, measured in seven to 10 runs with each method. Mean values for E2 in pooled sera deviated by 75% to 350% from the means measured with our routinely used extraction method. Between-run CVs ranged from 4% to 14% for the direct assays as compared with 10% for the extraction assay. We also investigated, for two of the direct assays, the effect of extraction with diethyl ether before radioimmunoassay, with respect to improvement in the agreement with our extraction method. All of the assays were easy to perform and results were obtained within 4-5 h, but we conclude that matrix effects may be expected in direct assays of estradiol.

Activity measurements of calcium, sodium, potassium, and chloride after equilibrium dialysis used to show lack of evidence for protein interference with calcium electrodes

We measured the activity of Ca2+, Na+, K+, and Cl- with ion-selective electrodes after equilibrium dialysis of solutions with different albumin concentrations. The calculated Donnan ratio was the same for all ions in the same solution and increased with the albumin concentration, as predicted by the Donnan theory. The Donnan distribution ratio for Ca2+ was similar, as determined with instruments from three different manufacturers. For healthy subjects and patients with renal stone disease, we did not find any correlation between serum concentrations of ionized calcium and albumin. The discordance between measured ionized calcium and albumin-corrected total calcium depended on the correction algorithm we utilized. The difficulties of absolutely proving or disproving a protein error in these measurements are discussed, but our data are not consistent with protein being a source of error in measurements of ionized calcium.

Activity measurements of calcium, sodium, potassium, and chloride after equilibrium dialysis used to show lack of evidence for protein interference with calcium electrodes

We measured the activity of Ca2+, Na+, K+, and Cl- with ion-selective electrodes after equilibrium dialysis of solutions with different albumin concentrations. The calculated Donnan ratio was the same for all ions in the same solution and increased with the albumin concentration, as predicted by the Donnan theory. The Donnan distribution ratio for Ca2+ was similar, as determined with instruments from three different manufacturers. For healthy subjects and patients with renal stone disease, we did not find any correlation between serum concentrations of ionized calcium and albumin. The discordance between measured ionized calcium and albumin-corrected total calcium depended on the correction algorithm we utilized. The difficulties of absolutely proving or disproving a protein error in these measurements are discussed, but our data are not consistent with protein being a source of error in measurements of ionized calcium.

Effect of tetrasodium EDTA on enzymatic determinations of urinary oxalate

We studied the effects of pretreating urine samples with tetrasodium EDTA (TEDTA) before measuring urinary oxalate with an enzymatic kit (Sigma). Mean analytical recovery of added oxalic acid was only 49% (SD +/- 13%) when the assay was performed as recommended by the manufacturer, but treating samples with TEDTA improved recoveries (96 +/- 10%). In 20 unselected 24-h urine samples assayed with and without TEDTA treatment, the mean oxalate concentrations were significantly (P less than 0.001) different: 15.6 +/- 8.7 and 12.2 +/- 7.9 mg/L, respectively. TEDTA-treated urine samples stored for 14 days at -20 degrees C lost 20% of their oxalate concentration. Use of TEDTA simplifies sample preparation by eliminating the alkalinizing step needed to dissolve EDTA or disodium EDTA.

Effect of tetrasodium EDTA on enzymatic determinations of urinary oxalate

We studied the effects of pretreating urine samples with tetrasodium EDTA (TEDTA) before measuring urinary oxalate with an enzymatic kit (Sigma). Mean analytical recovery of added oxalic acid was only 49% (SD +/- 13%) when the assay was performed as recommended by the manufacturer, but treating samples with TEDTA improved recoveries (96 +/- 10%). In 20 unselected 24-h urine samples assayed with and without TEDTA treatment, the mean oxalate concentrations were significantly (P less than 0.001) different: 15.6 +/- 8.7 and 12.2 +/- 7.9 mg/L, respectively. TEDTA-treated urine samples stored for 14 days at -20 degrees C lost 20% of their oxalate concentration. Use of TEDTA simplifies sample preparation by eliminating the alkalinizing step needed to dissolve EDTA or disodium EDTA.

Actual ionized calcium and pH in blood collected in capillary or evacuated tubes

Results are presented for the concentration of actual ionized calcium (cCa2+), the actual pH and ionized calcium at pH = 7.4 [cCa2+(7.4)] measured in capillary whole blood, venous serum from vacuum tubes (Venoject) and serum equilibrated to pCO2 approximately equal to 5.3 kPa from 57 renal patients. The mean value for cCa2+ was higher for venous serum than for capillary blood (1.29 mmol/l versus 1.26 mmol/l), corresponding to the difference in pH (in venous serum). This difference could be eliminated by separating the serum at 4 degrees C rather than room temperature. The cCa2+ (7.4) was the same for capillary blood, venous serum (Venoject) and equilibrated serum from blood collected in plain glass tubes, Venous serum could be stored at 4 degrees C for 4 h without significant change in cCa2+ and pH, and for 1 week at 4 degrees C for the measurement of cCa2+(7.4). In patients with acid-base disturbance cCa2+ is preferable to the measurement of cCa2+(7.4).

Changes in vitamin D metabolites and bone histology in rats during recovery from rickets

The relative roles of 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D (1,25-(OH)2D) and 24,25-dihydroxyvitamin D (24,25-(OH)2D) in bone mineralization are largely unknown. Young vitamin D depleted rats were fed increasing amounts of vitamin D and grouped radiologically in accordance with the rat line test. They ranged from severely rachitic to normal. Radiology was correlated with serum levels of 25-OHD, 1,25-(OH)2D, 24,25-(OH)2D, ionized calcium, magnesium, and phosphate, with bone histology, and with the total mineral content of the animals. Serum 1,25-(OH)2D rose in a linear fashion to supranormal values during bone healing and correlated with the radiological degree of rickets. Serum 25-OHD was below detection limit in the most rachitic and low in the radiologically normal rats, whereas 24,25-(OH)2D was low in all groups. These two metabolites showed no correlation with the radiologic, histologic or biochemical parameters. In rachitic rats, 1,25-(OH)2D appears to play a major role in bone healing and possibly exerts a direct effect on bone cells. It cannot be ruled out, however, that the effect is mediated through a rise in serum levels of calcium and phosphorus, although signs of bone healing were seen in the presence of a subnormal calcium X phosphorus product. Initiation of mineralization can take place with unmeasurable 25-OHD, and 24,25-(OH)2D seems to be without importance.

The calcium ion activity and the standardized excretion rate of calcium in urine of healthy adults

A standardized protocol is described for the study of the calcium excretion in urine. After 12 h of fasting, urine is collected during 4 h with a water load of 10 ml per kg body weight. Urine is also collected during the following 20 h period on the habitual water and calcium intake. Reference values for 48 healthy adults are given as 0.25 and 0.75 quantiles. The measured activity of calcium ions (Ca2+) in urine is 0.09-0.27 mmol/kg for the 4 h period, 0.34 to 0.52 mmol/kg for the 20 h period; pH values are 5.61-6.43 (4 h) and 5.46 to 6.04 (20 h). The concentrations of total calcium are 0.67-2.05 mmol/l (4 h) and 3.16 to 4.94 mmol/l (20 h). The value for the excretion rate of calcium (standardized to a creatinine clearance of 100 ml/min) is 1.30-3.24 mumol/min for the 4 h period and 3.06-4.88 mumol/min for the 20 h period, with no significant difference between the results for men and women. The relationship between the Ca2+ activity and pH was studied in urine titrated with HC1 or NaOH. In all urine the Ca2+ activity falls with increasing pH in a typical biphasic manner. This indicates the need for simultaneous measurement of the pH in order to interpret data for the Ca2+ activity in urine.

Measurement of ionized calcium with five types of instruments. An external quality assessment

An external quality assessment for ionized calcium determinations was carried out in 24 laboratories in Northern Europe. Both protein-free and protein-containing test materials were included in the study. The average within-laboratory variation (CV) for all test materials was 3.1, 1.7, 1.2, 1.8 and 1.3% for the AVL 980 (AVL, Graz, Austria), the Microlyte (Kone, Espoo, Finland), the Nova 2 (Nova Biomedical, Newton, Ma USA), the Orion SS-20 (Orion, Cambridge, Mass., USA), and the ICA1 (Radiometer, Copenhagen, Denmark) respectively. The corresponding interlaboratory CV was 3.1, 2.9, 3.1 and 2.4%. The variation between types of instruments was even larger and caused differences of up to 33%. The results indicate a need for well-defined protein-containing control material.

Sampling and storage of blood for determination of ionized calcium

We report some new procedures for the determination of ionized calcium using a semi-automatic ICA 1 analyser provided with a new flow-through tonometer unit, TNC 1, in connection with an automatic turntable. Ionized calcium calculated to a standard pH of 7.4 (cCa2+(7.4)) was not significantly different for capillary blood, venous blood and serum in healthy adults; however, a significant difference was found for actual ionized calcium (cCa2+). The effect of erythrocytes on the liquid junction potential was eliminated by use of a new salt bridge solution (sodium formate). Serum samples should be taken as anaerobically as possible to avoid precipitation of calcium complexes when pH increases above 7.9. For measurement of cCa2+-pH we developed special capillary tubes. Serum could be stored at 4 degrees C for 7 days and at -20 degrees C for 45 days without significant change in cCa2+(7.4). Capillary blood could be stored at 4 degrees C for 4 h without significant change in cCa2+ and pH or at 4 degrees C or 20 degrees C for 24 h without significant change in cCa2+(7.4). Vein puncture with stasis or muscular exercise caused only a small increase in cCa2+(7.4) (1.5%). The ingestion of food did not affect cCa2+ in healthy adults. 97.5% CO2 equilibrium was obtained in 3 min with the new flow-through tonometer.

Urinary cyclic AMP in spot urine of healthy children

We present reference values for the excretion of cAMP in spot urine collected between 09.00 and 12.00 hours in 143 healthy children aged 2-200 months. The excretion of cAMP was creatinine-corrected and expressed as a substance concentration ratio (UcAMP/crea)U due to a positive significant correlation between the excretion of cAMP and creatinine (r = 0.68, p less than 0.001). The mean value (95% significance limits) for (UcAMP/crea)U was 748 mumol/mol (254-2206 mumol/mol). A logarithmic transformation of the ratio was used, since preliminary analysis showed uneven distribution; when the logarithmic transformation was used, the data appeared evenly distributed. There was no significant difference between the results for girls and boys. The value of lg(UcAMP/crea)U was related to the age or body surface area with decreasing values at higher age or body surface area. (r = -0.55 and r = -0.57, p less than 0.001). Spot urine for measurement of urinary cAMP instead of a 24 h collection appears preferable due to the practicability of the test in children.

Extraction from bone powder: collagen, calcium and phosphate

A method for the estimation of the extraction rate is shown and exemplified by preliminary data from extraction of collagen, calcium and phosphate with EDTA and neutral salt solution. The initial extraction rate was high, even with neutral salt solution, and optimal extraction efficiency was obtained within 24 h.

Serum ionized calcium, nephrogenous and total urinary cyclic AMP and urinary phosphate in normal subjects

Total urinary cyclic AMP (UcAMP) and nephrogenous cyclic AMP (NcAMP) were measured in 4, 20 and 24 h urine in forty-eight healthy volunteers. There were no significant differences between 4, 20 and 24 h excretion rate of UcAMP and NcAMP whether it was corrected for the glomerular filtration rate [( UcAMP]GF, [NcAMP]GF), creatinine corrected (UcAMP/Crea)U, or expressed as actual excretion rate (NcAMP,n), nor any sex differences. Mean values +/- one standard deviation (SD) for these parameters: [UcAMP]GF: 30.4 +/- 9.4 nmol/l; 27.7 +/- 7.0 nmol/min; 28.1 +/- 6.9 nmol/l in 4, 20 and 24 h urine, respectively. [NcAMP]GF: 13.4 +/- 8.5 nmol/l; 10.6 +/- 7.7 nmol/l; and 11.1 +/- 7.2 nmol/l in 4, 20 and 24 h urine, respectively. (NcAMP,n): 1.45 +/- 0.90 nmol/min; 1.14 +/- 0.80 nmol/min; 1.17 +/- 0.73 nmol/min in 4, 20 and 24 h urine, respectively, NcAMP accounts for about 40% of UcAMP. A positive correlation was found between plasma cyclic AMP and [UcAMP]GF (r = 0.41, P less than 0.001), whereas this relationship could not be demonstrated between plasma cyclic AMP and [NcAMP]GF (r = -0.008, P greater than 0.1). The calculation of [NcAMP]GF therefore corrects for unsuspected high or low plasma cyclic AMP values, and is therefore the preferred parameter of the PTH effect on the kidney tubular cells. No correlation could be demonstrated between [NcAMP]GF and concentration of ionized calcium in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of sodium and potassium with ion-selective electrodes

We compared different sample-handling techniques for measurement of Na+ and K+ with ion-selective electrodes (ISE). Imprecision was less for venous blood (with a minimum of heparin) than for plasma, serum, or capillary blood. The results for K+ were higher for serum than for whole blood, and higher for whole blood than for plasma. The latter difference was apparently due to release of K+ during the analysis. Values were more stable for whole blood stored at 20 degrees C than at 4 degrees C or 37 degrees C. The molality of Na+ in the plasma of mixed whole blood changed by -10.5 mmol/kg per unit change in blood pH. This could be explained by the different H+ buffering capacities of plasma and erythrocyte fluid, because when the pH is changed, the concentration of small anions in erythrocytes changes more than it does in plasma, with a consequent osmotic movement of water across the erythrocyte membrane. When we took into account the residual liquid-junction potential and the mass concentration of water in each of 65 patients' sera, the molality determined for Na+ was 1% lower and that of K+ 3% lower by ISE than by flame photometry--differences that may be related to ionic binding or to a lower molal activity coefficient in serum than in the calibrator.

Determination of sodium and potassium with ion-selective electrodes

We compared different sample-handling techniques for measurement of Na+ and K+ with ion-selective electrodes (ISE). Imprecision was less for venous blood (with a minimum of heparin) than for plasma, serum, or capillary blood. The results for K+ were higher for serum than for whole blood, and higher for whole blood than for plasma. The latter difference was apparently due to release of K+ during the analysis. Values were more stable for whole blood stored at 20 degrees C than at 4 degrees C or 37 degrees C. The molality of Na+ in the plasma of mixed whole blood changed by -10.5 mmol/kg per unit change in blood pH. This could be explained by the different H+ buffering capacities of plasma and erythrocyte fluid, because when the pH is changed, the concentration of small anions in erythrocytes changes more than it does in plasma, with a consequent osmotic movement of water across the erythrocyte membrane. When we took into account the residual liquid-junction potential and the mass concentration of water in each of 65 patients' sera, the molality determined for Na+ was 1% lower and that of K+ 3% lower by ISE than by flame photometry--differences that may be related to ionic binding or to a lower molal activity coefficient in serum than in the calibrator.

Sex-dependent relation between ionized calcium in serum and blood pressure

In an epidemiological study of 977 45-year-olds, both the mean concentration of ionized calcium in serum, [Ca2+]7.4, and arterial blood pressure were higher in men than in women. Among the men, there was a weak positive correlation between [Ca2+]7.4 and the systolic blood pressure, but no other significant correlation was found within each separate sex. Postmenopausal women had slightly increased [Ca2+]7.4 but normal blood pressure. Patients taking thiazide diuretics or beta-adrenergic blocking agents had normal [Ca2+]7.4.