Identification and treatment of hypomagnesemia and hypokalemia in patients receiving digoxin.

Hamsters are increasingly used for comparative study of cholesterol metabolism (1). To assess the validity of differential precipitation with Mg2 4-phosphotungstate for quantification of plasma high-density-lipoprotein cholesterol (HDLC), we did a method-comparison with ultracentrifugal flotation. The precipitating reagent, 0.55 mmolJL phosphotungstic acid and 25 mmol/L magnesium chloride, was used as recommended by the manufacturer (Boehringer Mannheim Diagnostics, Indianapolis, IN). Highdensity-lipoprotein fractions in plasma were isolated in a potassium bromide/sodium chloride adjusted density range of 1.063-1.210 kg/L by analytical ultracentrifugation. Cholesterol concentrations were determined spectrophotometrically with an enzymatic cholesterol reagent containing microbial cholesterol esterase, in an Hitachi 705 clinical chemistry analyzer (Boehringer Mannheim Diagnostics). Adult male Golden Syrian hamsters (n = 32) were fed a pelleted-grain-based diet (Purina Rodent Laboratory Chow, St. LOUiS, MO), either with or without 2 g of cholesterol added per kilogram. Half of the animals consuming each diet were fasted for18 h before blood sampling. Differential precipitation was highly associated (y = 1.02x + 0.02; r = 0.99) with ultracentrifugal flotation for isolation and quantification of HDLC (range 310-950 mg/L) regardless of feeding status or diet. The mean was 650 (SE 40) mgfL for differential precipitation and 640 (SE 30) mg/L for ultracentrifugation. The relative analytical error for the differential-precipitation method was 1.6%. Differential precipitation with Mg-phosphotungstate evidently is a valid alternative to ultracentrifugation for measuring HDLC in plasma from hamsters.