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PubMedDate not supplied

Renal tubular acidosis type 2 with Fanconi's syndrome, osteomalacia, osteoporosis, and secondary hyperaldosteronism in an adult consequent to vitamin D and calcium deficiency: effect of vitamin D and calcium citrate therapy.

OBJECTIVE: To describe a unique example of renal tubular acidosis type 2 (RTA 2) in conjunction with Fanconi's syndrome and osteomalacia consequent to vitamin D and calcium deficiency in an adult without underlying gastrointestinal disease. METHODS: We review the clinical, hormonal, histomorphometric, and micro-computed tomographic findings and the response to therapy with vitamin D and calcium in our patient. RESULTS: On admission, a 33-year-old African American woman had the following laboratory findings: serum ionized calcium 3.8 mg/dL (0.95 mmol/L), venous pH 7.26, bicarbonate 20 mEq/L, chloride 111 mEq/L, alkaline phosphatase 1,192 U/L (20.26 microkat/L) (normal, 40 to 136 U/L), 25-hydroxyvitamin D <5 ng/mL (<12 nmol/L) (normal, 10 to 60 ng/mL), parathyroid hormone 1,620 pg/mL (165.2 pmol/L) (normal, 10 to 60 pg/mL), aldosterone 68.4 ng/dL (1,894.7 pmol/L) (normal, 4.5 to 35.4 ng/dL), supine plasma renin activity 19.8 ng/mL per hour (5.35 ng/L per second) (normal, 0.5 to 1.8 ng/mL per hour), and aminoaciduria. A lumbar spine bone density T-score was -4.6, and a femoral neck T-score was -4.9. An undecalcified tetracycline-labeled bone biopsy specimen showed severe osteomalacia, severe osteoporosis, and peritrabecular fibrosis. A small intestinal biopsy revealed normal findings. Results of an ammonium chloride loading test and a bicarbonate infusion test were consistent with RTA 2. After 24 months of vitamin D and calcium therapy, results of serum and urine chemistry studies and bicarbonate infusion normalized. The lumbar spine T-score improved to -2.0, and the femoral neck T-score improved to -2.7. Bone biopsy specimens demonstrated resolution of the osteomalacia. CONCLUSION: Nutritional vitamin D and calcium deficiency may cause RTA 2, Fanconi's syndrome, and osteomalacia in adults as well as in children.

Acidosis, Renal Tubular↗
PubMed1996

Interaction of citric acid with hydroxyapatite: surface exchange of ions and precipitation of calcium citrate.

The use of citric acid is efficacious and distinctive in the demineralization of dentinal root surfaces for periodontal regeneration and in the etching and conditioning of enamel or dentin for bonding restorative resins. To decipher the role of citric acid in these applications, it is important that one have a basic understanding of its interaction with synthetic hydroxyapatite. The uptake or removal of citrate ions from aqueous solutions of citric acid (4 to 100 mmol/L, 10 mL) by hydroxyapatite (1 g) was studied at 22 degrees C after a given reaction period (from 3 hr to 11 days) by immediate spectrophotometric monitoring of the concentrations of the filtrates (214 nm). The concentrations of calcium, phosphate, and hydrogen ions were also determined in the same solutions. The interaction: (i) is a time-independent ionic-exchange process with the substrate when the initial acid concentrations are dilute (4 to 12.5 mmol/L), and (ii) is a reactive process that is time-dependent for higher acid concentrations. The exchange process shows an adsorption of about one citrate ion per (100) face of the unit cell of hydroxyapatite for a maximally exchanged surface. The curves representing the reactive process may be quantitatively or qualitatively explained on the basis of the supersaturation of the solutions with respect to calcium citrate and its slow precipitation. The physico-chemical analysis of the needle-shaped birefringent crystals of the precipitate from the supersaturated solutions confirms the precipitate to be Ca3(citrate)2.4H2O.

Acid Etching, Dental↗
PubMedDate not supplied

The effect of citrate, calcium, and magnesium ions on the potassium movement across the human platelet membrane.

The intracellular K+ concentration in platelets is reduced during storage in citrated plasma. As shown previously, pH has a marked influence on this reduction. The effect of citrate and Ca2+ and Mg2+ on the K+ permeability of the membrane and on the active K+ transport across the membrane was investigated. Platelets were incubated in dialyzed plasma at 37 degrees C, pH 5.5 to 7.9, with and without added Ca2+ and Mg2+ and citrate. After 60- to 120-minute incubation, a steady state was reached, and ouabain was added to inhibit the active K+ transport. In the pH interval 5.5 to 6.2 citrate, Ca2+ and Mg2+ had no influence on either the active K+ transport or the K+ permeability. Between pH 7.1 and 7.9, Ca2+ and Mg2+ decreased the permeability, whereas citrate increased it. At pH 7.9, citrate had a depressing effect on the active transport. These results indicate that a low citrate concentration and a pH below 7 are important for maintaining a high intracellular K+ of platelets during storage in plasma.

Blood Platelets↗
PubMed1993

Creatinine, calcium, citrate and acid-base in spinal cord injured patients.

The aim of this work was to recognise factors responsible for reduced citrate excretion, previously reported in patients with spinal cord lesions and possibly related to the occurrence of urinary tract stone or catheter blockage. Inter alia, a reference range for creatinine in plasma (34-88 mumol/l) was also obtained. Two groups of subjects were studied. The first group consisted of 64 male inpatients with spinal cord lesions and 20 male control subjects. The second group were 342 spinal patients who attended an outpatient clinic and 31 control subjects. Plasma calcium was within the normal range but higher in patients within 1 year of onset of the cord lesion than it was later or than was found in control subjects. Plasma pH and bicarbonate were within the normal range but higher in the patients than in the control subjects. When patients with urea-splitting infection were omitted the patients had a higher urinary pH and a lower urinary ammonium than the controls. Urinary and plasma citrate were lower in the patients than in the controls. Urinary citrate was related to urinary potassium and creatinine clearance. Fractional renal tubular reabsorption of citrate did not differ between patients with normal renal function and control subjects. Patients with normal glomerular filtration had lower filtered load of citrate than the controls. The coincidence of relative alkalosis and reduced citrate excretion may be relevant to the understanding of catheter blockage and urinary stone formation in spinal cord injured patients.

Acid-Base Equilibrium↗
PubMed1984

Citrate activation of NAD-specific isocitrate dehydrogenase from bovine heart.

NAD-dependent isocitrate dehydrogenase from bovine heart was activated by lower concentrations of citrate in the presence of ADP (apparent S0.5 citrate = 0.033 mM) than in its absence (apparent S0.5 citrate = 2.64 mM) at low magnesium DL-isocitrate (0.18 mM) and free DL-isocitrate3- (0.45 mM) concentrations. Under these conditions, citrate (0.3 mM) lowered the apparent S0.5 for ADP from 0.24 to 0.05 mM. The binding of NAD+ was unaffected by citrate; however, saturating concentrations of citrate lowered the apparent S0.5 for magnesium isocitrate from 0.63 to 0.19 mM in the presence of ADP. Citrate does not appear to bind to the regulatory or catalytic magnesium isocitrate-binding sites, since the Hill coefficient for magnesium isocitrate was not lowered by citrate nor did inhibition occur at high citrate concentrations. The data suggest that magnesium citrate was the activating species. Citrate activation occurred from pH 6.5 to 8.0. As with magnesium citrate, calcium citrate lowered the S0.5 for magnesium isocitrate (apparent S0.5 for calcium citrate = 0.26 mM), and it did not appear to bind to the regulatory or catalytic magnesium isocitrate-binding sites. However, in contrast to the substantial facilitation of magnesium citrate activation by ADP, no activation by calcium citrate occurred in the presence of ADP. Differences in the mechanism of activation of the enzyme by magnesium citrate and calcium citrate were also indicated by the finding that, whereas a number of tricarboxylates could replace citrate as an activator with Mg2+ as the sole divalent cation activator, only citrate was effective for the further enhancement of velocity by added calcium.

Adenosine Diphosphate↗