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.

Risk factors for urinary tract calculi in Trinidad

OBJECTIVE: To identify risk factors for urinary tract stones in Trinidad and Tobago. METHODS: A consecutive series of patients presenting to institutions in Trinidad for the management of proven urinary tract calculi was interviewed by questionnaires designed to obtain data on age, gender, ethnicity, occupation, stone location, a family history of stone disease, a past history of certain medical diseases and a semiquantitative estimate of the magnesium intake in food, 'over the counter' drugs and drinking water. An equivalent number of patients attending the same institutions for follow-up and verified from hospital records as having a previous radiological diagnosis of urinary tract stones, as well as a group of asymptomatic members of the community working in the same area, underwent the same interview. Chi-square, anova and Kruskal-Wallis tests were used to examine differences between the groups. Multiple logistic regression analysis was used to determine persistence of the significance of these differences after controlling for confounding variables. RESULTS: Data sufficient for analysis were obtained for 122 previous and 102 prospective patients and 102 controls. The mean age of the patients was 32 years. The ratio of males to females was 0.9-1.8:1 for the affected groups, but significantly more males than females had calculi in the lower urinary tract (19% vs. 6%; P = 0.004). More patients (30%) than controls (7%) gave a positive family history of urinary tract stone disease (P < 0.001). Affected persons had a lower dietary magnesium intake (P = 0.003), which accounted for a significantly lower total magnesium intake (P = 0.02). Logistic regression analysis of the variables studied indicated that independent predictors of the disease were a positive family history (P = 0.001), total magnesium intake (P = 0.001) and age (P < 0.001). CONCLUSION: A low magnesium intake and a positive family history are highly predictive of urinary tract calculi in this population

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)

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)

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)

Total body potassium, muscle electrolytes, and glycogen in malnourished children

Total body potassium, muscle potassium, magnesium, and glycogen have been estimated in infants while they were malnourished, during recovery, and in several after they were fully recovered. Muscle potassium was curvilinearly related to the total body potassium. Muscle magnesium was reduced, and the potassium/magnesium ratio was depressed in children with low muscle potassium values, implying differential loss of muscle potassium. Muscle potassium was linearly related to muscle glycogen. Twenty-four-hour urinary excretion of creatinine was measured; by assuming that 1 mg. of creatinine was derived from 20 Gm. of muscle, calculations of muscle mass were made. In children with a total body potassium over 40 mEq. per kilogram of body weight, muscle potassium contributed approximately one half of the total body potassium; this ratio decreased significantly when body potassium fell to very low values. (AU)

Chemical composition of organs of children who died from malnutrition

Chemical analysis was carried out on samples of brain, liver, skeletal muscle, heart and kidney obtained from children who died of malnutrition. Total body potassium was measured before autopsy by the 'whole body counting' technique. There was a marked increase in liver fat, and the brain contributed a higher percentage of the body-weight in the more severely malnourished children. All the organs had approximately the same concentrations of non-collagen nitrogen. The proportion of collagen was highest in muscle. All organs were depleted of potassium, but the muscle was most severely affected. Brain potassium as a percentage of total body potassium was higher than normal in the most severely potassium depleted children. Measurements of tissue magnesium showed that there was no difference in magnesium content of tissue when expressed in terms of non-collagen nitrogen. When compared with normal values, muscle was magnesium depleted. The potassium to magnesium ratio was lowest in muscle. (AU)

Magnesium balance studies in marasmic kwashiorkor

Studies of magnesium balance were made on 3 Jamaican infants during recovery from marasmic kwashiorkor. Analysis of muscle biopsy specimens indicated a marked deficit of magnesium as well as potassium in all cases. The serum magnesium level was slightly low in one case. A positive magnesium balance was maintained for several weeks in recovery and was accompanied by low urinary excretion. In one case there was considerable intestinal absorption of magnesium, even in the presence of diarrhea. Efficient absorption of a high oral suppliment tended to overcome renal conservation. Previous analysis has suggested that the deficiency of intracellular electrolytes in wet muscle samples is due partly to the reduced intracellular volume associated with protein loss and partly to a true electrolyte deficit. The positive magnesium balance in recovery is therefore attributable both to intracellular repletion and to tissue growth; the latter tends to be masked clinically by loss of excess body water. Little is known of the additional factor of the repletion of magnesium in bone, but the evidence from animal experiments is that the deficit in bone may be very substantial (AU)

The estimation of magnesium in small biological samples by flame spectrophotometry

Studies of human magnesium in this laboratory called for a simple method of estimating the magnesium comtent of large numbers of small biological specimens (Montgomery, 1960). It has been found that a technique involving the Unicam S.P. 900 flame spectrophtometer fulfils this need. Estimations have been made on serum, red cells, urine, and acid digests of muscles and faeces. A standard instrument was used, burning acetylene and air, with a new standard atomiser containing a metal jet. Readings were made at the atomic line of 285.2mu (AU)

Magnesium metabolism in the malnourished infant (abstract only)

Experimental depletion of magnesium in animals has been shown to induce a parallel, and even greater, depletion of potassium in the body tissues. It has been suggested that this might be due to interference with magnesium-dependent enzymes required for the maintenance of normal potassium balance within the cell. These observations have not hitherto had any direct application in natural human states. This paper describes the results of analysis of the electrolyte content of muscle biopsy specimens in 20 infants with severe protein malnutrition before and after recovery, and in 12 fatal cases. Magnesium was estimated by a new technique of flame spectrophotometry. A gross depletion of muscle magnesium was demonstrated, which closely paralleled that of potassium. These changes were not reflected in the magnesium content of serum or red cells. Estimations of seventy 24hr. urine specimens in recovering infants showed an avid magnesium retention prolonged over many weeks, in contrast to the brief conservation of potassium and phosphorous. The contents of both magnesium and potassium in the muscle of clinically recovered infants were still markedly below normal levels. The significance and possible applications of these findings are discussed (AU)