Calcium: beyond bones

It is well established that an adequate intake of the mineral calcium is essential for health bones and teeth. Did you know that calcium also plays an important role in other systems of the body? It circulates in the blood to carry out important functions relating to the clotting of blood, regulation of muscle contraction, transmission of nerve impulses, and maintaining a steady heartbeat. Some studies arre suggesting that calcium may also play a role in weight loss, prevention of colon cancer, the control of cholesterol and blood pressure. along with alleviating pre-menstraul symptoms. Is this really so? In this issue of Nayam News we will look at some of these findings, discuss the key functions of calcium in the body and highlight the dietary sources of this nutrient.

The relationship of magnesium intake to serum and urinary calcium and magnesium levels in Trinidadian stone formers

BACKGROUND:  The present study was undertaken to investigate the relationship between the dietary intake of magnesium and the serum and urinary levels of calcium and magnesium in a group of Trinidadian stone formers. METHODS:  A group of 102 confirmed stone formers presenting to urological clinics were interviewed using a questionnaire designed to obtain a semi-quantitative estimate of their oral magnesium intake. Patients were invited to give blood samples for serum calcium and magnesium levels and to provide 24-h urine specimens for the measurement of urinary levels of these minerals, as well as total urinary volumes. A group of 102 controls was subjected to a similar interview and blood and urinary testing. Chi-square tests and Student's t-tests were used to examine group demographic differences. The Mann–Whitney test investigated differences in biochemical indices. Binary logistic regression was used to identify predictors of stone formation. RESULTS:  Blood samples were obtained from 60 patients and 98 controls. Urine samples were returned by 34 patients and 97 controls. Only 10 stones were retrieved from patients. Patients had a significantly lower magnesium intake, but higher median serum and urinary calcium levels, and higher serum calcium to magnesium ratios than controls. Independent variables capable of predicting stone formation included total magnesium intake and serum and urinary calcium levels. CONCLUSIONS:  Increased serum and urinary calcium levels, calcium to magnesium ratios, and a low magnesium intake were predictive of stone formation in this Trinidadian population.

Serum calcium and vitamin D status of patients with sickle cell disease in Curacao: comparison with Saudi Arabia

Data from Saudi Arabia suggest that low vitamin D status is involved in skeletal abnormalities of patients with homozygous sickle-cell disease (HbSS). We measured parameters of calcium homeostasis and vitamin D status in HbSS patients (median age: 8 years, range: 3-19; 8 females, 10 males) and matched HbAA controls living in the tropical island of Curacao. Serum calcium of HbSS patients (2.32 ñ 0.07 mmol/l) was lower (ANCOVA, p = 0.002) than that of HbAA controls (2.44 ñ 0.14). None of the subjects had hypocalcaemia. There were no differences in phosphate, total protein, albumin, intact parathyroid hormone (PTH), 25-hydroxyvitamin D [25(OH)D; HbSS 87 ñ 27, HbAA 86 ñ 15 nmol/l] and 1,25-dihydroxyvitamin D. There were no significant relationships between serum calcium and albumin, calcium and total protein, and PTH and 25 (OH)D. Our data suggest that hypocalcaemia and hyperparathyroidic tendencies in Saudi Arabian HbSS patients are likely to be caused by the locally poor vitamin D status, attributable to insufficient exposure to direct sunlight (AU)

The role of urinary calcium, magnesium, phosphate and creatinine as possible predictors of pre-eclampsia in Trinidadian parturients - abstract

One hundred pregnant women between 24 and 28 weeks' gestation attending the antenatal clinic at the Mount Hope Women's Hospital and the Port-of-Spain General Hospital were admitted to the study. Women with a history of evidence of renal disease, diabetes chronic hypertension, cardiovascular disease, proteinuria or any other chronic medical illness were excluded. Urine and blood samples were collected at the first and each subsequent visit and bi-weekly if the subject was hospitalised. The urinary and serum concentrations of total calcium, magnesium and phosphate were measured by atomic absorption spectrometry. After delivery, the patients' notes were analysed to determine the development of pre-elcampsia (PE). The purpose of the study was to evaluate urinary calcium, magnesium and phosphate as early predictors of PE. Eight women satisfied the criteria for PE and differed from the 92 normotensives as shown (Table). Urinary calcium and magnesium and birthweight were significantly lower in PE as compared to normal pregnant women. The gestational age, urinary phosphate and serum values were no different in the two groups (AU)

Calcium permeability in deoxygenated sickle erythrocytes - abstract

Sickle cell have an abnormally high level of calcium and, by an unknown mechanism, exhibit an increase in Caý+ permeability when they are sickled upon deoxygenation. This reversible increase in Caý+ permeability might contribute to cell dehydration by activation of K+ and water loss through the Caý+ permeability might contribute to cell dehydration by activation of K+ and water loss through the Caý+ dependent K+ channel (Gardos pathway). In the present study, the mechanism involved in Ca+ influx stimulation in sickle cells induced by deoxygenation was investigated by three different experiments: Ca2+uptake (1) in the presence of an extracellular impermeant marker to test endocytosis, (2) in the presence of the Caý+uptake (1) in the presence of an extracellular impermeant marker to test endocytosis, (2) in the presence of the Caý= -channel inhibitor Nifedipine, and (3) in the presence of an anion-exchanger inhibitor 4,4' - diisothiocyanatostilbene-2,2' - disulfonic acid (DIDS). These experiments revealed that endocytosis accounted for 6 percent to 19 percent of the Ca2+ uptake in deoxygenated sickle cells a nd that the increased Ca2+ influx was in part blocked by Nifedipine and by DIDS. The present findings, describing different pathways involved in the Caý+ increased permeability of deoxygenated sickle cells are of potential therapeutic interest (AU)

Activation of the alternative pathway of human complement by haemoglobin

Haemoglobin solutions (concentration >1.5mg/ml), prepared from lysates of erythrocytes from a normal subject and from a patient with sickle cell anaemia, caused factor B and C3 cleavage and loss of haemolytic activity of factor B when incubated with fresh autologous serum. Under the same experimental conditions, preparations of erythrocyte stroma or of buffy coat lysates did not produce factor B and C3 cleavage. This reaction required Mg++ but not Clq or C4, indicating that the alternative complement pathway was activated (Summary)

Vitamin-D deficiency rickets in Jamaican children

Vitamin-D deficiency is not as rare in Jamaica as previously believed. 9 children with vitamin-D deficiency rickets have been seen at the University Hospital of the West Indies during the past 5 years. All were over 3 years of age at time of presentation. Both dietary deficiency of vitamin-D and lack of exposure to sunlight seem to be important causes. Children living in rural Jamaica seem to be more susceptible to the disease than those living in a city, due perhaps to more prolonged breast feeding and lack of fortified milk feeds on weaning.(AU)

Regulation of renal cortex ammoniagenesis. I. Stimulation of renal cortex ammoniagenesis in vitro by plasma isolated from acutely acidotic rats

We studied the acute renal metabolic response in rats made acidotic by a single oral dose of ammonium chloride. Cortical slices from acutely (2-h) acidotic rats utilized more glutamine and produced more ammonia and glucose from glutamine than slices from normal animals. When cortical slices from normal rats were pretreated in vitro with plasma isolated from acutely acidotic rats, they achieved similar increases in glutamine utilization, ammonia formation, and gluconeogensis from glutamine. We did not observe such stimulation in normal cortical slices pretreated in a low pH-low bicarbonate medium. Our data show that a non-dialysable factor is present plasma from acutely acidotic rats that may be responsible for the early increase in the urinary ammonia observed in such animals (AU)

A study of stabilization of gluconeogenic activity in rat liver slices by calcium and manganese ions

The effect of some bivalent cations on gluconeogenesis by the rat liver-slice preparation has been investigated. Ca2+ and Mn2+ stimulated glucose production from a range of substrates but not from glycerol. Mg2+ had no effect on the rate of glucose production. Ca2+ were required to maintain phosphoenolpyruvate carboxylase activity in the slice preparation. Ca2+ and Mn2+, but not Mg2+, retarded the release of lysosomal enzymes from the slice into the incubation medium. It is proposed that Ca+ and mn2+ stimulate glucose production by stabilizing the lysosome system in the liver-slice preparation. The value of the liver-slice preparation as a means of measuring hepatic gluconeogenesis is discussed (AU)

Studies of pulmonary alveolar microlithiasis and pulmonary alveolar proteinosis

A case of pulmonary alveolar microlithiasis and a case of pulmonary alveolar proteinosis in West Indian patients are described. A course of therapy with a chelating agent produced no roentgenologic improvement in alveolar microlithiasis. The pathology of these diseases is briefly reviewed, and the possible interrelations of pulmonary alveolar microlithiasis, pulmonary alveolar proteinosis, and pulmonary corpora amylacea are discussed (Summary)

Calcinosis

Two cases of "idiopathic" calcinosis in young boys are reported. One patient received no treatment; in the other, rapid recurrence, followed excision. Both patients are well two and a half years and one and a half years, respectively, after the diagnosis was made and show no evidence of collagen disease. The literature is reviewed (Summary)