Urinary excretion of magnesium in man

Roles of divalent cations and pH in mechanism of action of nitroxoline against Escherichia coli strains

The antibacterial activity of nitroxoline (NIT), an antibiotic used in the treatment of acute or recurrent urinary tract infections caused by Escherichia coli, is decreased in the presence of Mg2+ and Mn2+ but not Ca2+. In order to elucidate the interaction between this drug and the divalent cations, spectrophotometric studies based on the natural absorption of the nitroxoline moiety were conducted. In the presence of the divalent metal ions, a shift in the NIT A448 suggested the formation of drug-ion complexes, for which the stability followed the order Mn2+ > Mg2+ > Ca2+. A clear correlation was found between the chelating property and antibacterial activity of NIT; both were pH dependent. A convenient colorimetric method for the determination of NIT uptake by bacterial cells was also developed. Uptake was energy independent and showed biphasic kinetics: a rapid association with cells and then a slower increase in cell-associated NIT which reached a plateau. NIT uptake was reduced in the presence of magnesium. The implications of metal ion complexation and pH on the clinical efficacy of NIT are discussed.

Magnesium and its therapeutic uses: a review

Magnesium has been reported as an effective medical therapy in an expanding array of conditions. Evidence investigating magnesium's use is presented, with a number of studies suggesting it should be seriously considered in such conditions as ischemic heart disease, cardiac arrhythmias, and asthma. Magnesium balance and metabolism are briefly reviewed, and then various hypotheses are presented that may explain magnesium's physiologic mechanisms of action, most likely involving calcium and potassium flux across cellular membranes in smooth muscle. In a number of the conditions to be discussed, it has been uncertain whether magnesium administration serves the purpose of merely correcting an underlying deficiency state or of utilizing a specific pharmacologic effect of magnesium. Magnesium deficiency is a relatively common condition, and predisposing factors as well as recent methods for assessing total body stores of magnesium are discussed. Physicians should be familiar with the numerous conditions and therapeutics that are risk factors for an underlying magnesium deficiency and in which empiric magnesium replacement should be considered. Guidelines for administration of parenteral magnesium are presented with specific focus on the low risk of adverse effects, as suggested by the large and rapid dosing regimens used in many of the clinical studies discussed here.

Metal concentrations in human pancreatic juice

Concentrations of 11 metals (cadmium [Cd], lead [Pb], copper [Cu], iron [Fe], manganese [Mn], cobalt [Co], chromium [Cr], nickel [Ni], zinc [Zn], magnesium [Mg], and calcium [Ca]) and protein in human pancreatic juice were studied. Human pancreatic juice was sampled by endoscopic cannulation after administration of secretin (intravenous [i.v.], 1 mu/kg). There were 19 subjects (11 males and 8 females) and the means of their ages were 50.3 yr (male, 20-68 yr) and 52.5 yr (female, 45-64 yr). Diagnoses were: normal, 5; early pancreatic cancer, 9; and chronic pancreatitis, 5. None had symptoms suggestive of disturbances in endocrine and exocrine functions of the pancreas. Concentrations of metals and protein in pancreatic juice did not change significantly between males and females or with pathological changes in the pancreas. Assuming the flow rate of pancreatic juice to be 1500-2000 ml/day, the daily excretions of metals into duodenum via pancreatic juice were calculated as follows (mumoles of metal/day): Cd, 0.012-0.012; Pb, 0.216-0.288; Cu, 6.20-8.26; Fe, 2.34-3.12; Mn, 0.100-0.133; Co, 0.165-0.220; Zn, 7.46-9.94; Cr, 0.084-0.112; Mg, 274.1-365.4; Ni, 1.64-2.18; and Ca, 0.221-0.295. Toxic (Cd and Pb) and essential metals (Cu, Zn, Fe, Mn, Cr, and Ni) are excreted daily into duodenum via pancreatic juice.

Selective deficiency of 1,25-dihydroxycholecalciferol. A cause of isolated skeletal resistance to parathyroid hormone

To investigate the role of vitamin D metabolites in the pathogenesis of pseudohypoparathyroidism, we studied an elderly man with a unique variant of the disease, which was characterized by hypocalcemia, elevated serum parathyroid hormone (513 +/- 13 pg per milliliter, mean +/- S.E.M., normal, less than 450) but normal renal responses (phosphate and cyclic AMP) to exogenous parathyroid extract. Treatment with parathyroid extract did not produce a calcemic effect, suggesting an isolated skeletal hyporesponsiveness to parathyroid hormone. Although 25-hydroxyvitamin D levels were not reduced, levels of 1,25-dihydroxycholecalciferol were extremely low (0.52 ng per deciliter; normal 3.3 +/- 0.06, S.D.). Treatment with 1,25-dihydroxycholecalciferol (1 microgram by mouth per day for four days) increased circulating levels to normal (4.60 ng per deciliter) and restored to normal the calcemic response to parathyroid (change in calcium 3.0 mg per deciliter). These data suggest that 1,25-dihydroxycholecalciferol deficiency may explain the skeletal resistance, but not the renal resistance, often present in classic pseudohypoparathyroidism.