A. Cambi

A. Clerico

L. Cecchini

M.G. Del Chicca

S. Giaconi

CLERICO, ALDO

M. G. Del Chicca

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CLINICALCHEMISTRY, Vol.34, No. 1, 1988 215errors ofmetabolism currently dependson sophisticated biochemical analysis.NMR analysis can simultaneously an-alyze the mixture of compounds in bio-logical fluids, but complete analysis ofbiological fluids by NMR will not benecessitated. Accurate diagnosisshould await the results by authenti-cated methods. Quickness is impor-tant.As might be seen from our paper, theneed to pretreat urine to compensatefor the signals of glycerol is only appli-cable to glyceroluria, which is veryrare. Our method will be used for so-lected cases for clinical use; it shouldsuffice for clinical screening.NMR analysis of freeze-dried (andredissolved in DM80) samples of biologi-cal fluid had not been reported. Wilsonand Nicholson reported the absence ofa signal of urea in the conventionalmethod, but detected it in the freeze-driedJDMSOsolution. This phenomenonis well known and is not new.Both the careful clinician’s eye and. the quick screening of biological fluidwill afford several important pieces ofinformation that one would not be ableto get by using only a higher magneticfield NMR spectrometer. Comparisonsofthe ability ofvarious N.MR machinesis not a usual goal for researchers, Iguess.Shuichi YamaguchiSaitama Children’s Med. Ctr.Iwatsuki, Saitama, JapanUrinary Excretion of Digoxln-IlkeImmunoreactlvity after PhysIcalExerciseTo the Editor:Several studies (for review see refs.1-4) document the presence of an en-dogenous substance or group of sub-stanceswith digoxin-like immunoreac-tivity (DLIS) in blood of experimentalanimals and humans, found when RIAor enzyme iminunoassay methods areused for assay of digoxin. Experimen-tal studies and theoretical consider-ations suggest that DLIS might be anendogenous modulator of Na/K-transporting ATPase (EC 3.6.1.37; thereceptor of cardiac glycosides) and playa role in the regulation of fluids andelectrolytes,as well as in the pathogen-esis of several cardiovascular and kid-ney diseases (1, 3, 4). In a previouspreliminary study (5), DLIS concentra-tions in serum have also been shown toincrease after strenuous physical activ-ity.Because DLIS concentrations inplasma or serum samples from normaladult subjects are frequently near thelimit ofsensitivity for RIA methods (6-8), the sample usually must be concen-trated before analysis, to increase theprecision of the assay. In contrast,urine of adults and newborns haveDLIS concentrations four- to sixfoldthose in plasma, and the direct RIAcould be preferable (8).To investigate whether urinary ex-cretion ofDLIS increases during physi-cal activity, concomitantly with thepreviously reported (5) increase in so-rum, we measured the urinary excre-tion rate of DLIS in two groups ofathletes, at rest and after a trainingsession.We measured urinary DLIS by apreviously reported solid-phase RIAmethod (6, 7) in which digoxin cbs-solved in a buffer containing 40 g ofhuman serum albumin per liter is usedas standard, 1mIlabeled digoxin astracer, and solid phase (antibody-coat-ed test tubes) for bound/free separa-tion. Results are expressed as digoxinequivalents.We directly assayed 0.2-mL samplesofurine. The mean sensitivity obtainedin 20 separate experiments, performedduring nine months, was 2.98 (SD1.11) pg per tube. The between-assayCV ranged between 10% and 20%.We studied nine female volleyballathletes (ages 17-24 y) and 13 malecyclists (21-37 y). The women collectedurine samples 2 h before and just aftera 2-h training session(energy expendi-tore about 200-250 kcallh). The mencollected 24-h urine samples (the timeof collection was exactly recorded) dur-ing a day of training (5 h of training,energy expenditure about 400-450kcallh). In addition, we studied a con-trol group of 22 normal subjects (10men and 12 women, ages 22-55 y), whoalso collected 24-h urines during a dayof normal activity (the time of collec-tion was also exactly recorded).The mean daily urinary excretionrate ofDLIS by the 22 normal subjects[84.97 (SD 31.35) pg/minI significantlyexceeded (P <0.05) that observed inthe 13 cyclists [66.92 (SD 17.17) pg/mini. The mean urinary excretion rateof DLIS found before exercise [88.90(SD 83.71) pg/mini in the nine volley-ball athletes was higher, though notsignificantly so (P = 0.374, paired t-test), than the value observed aftertraining [64.80 (SD 29.10) pg/minI.Thus we saw no increase in theurinary excretion of DLIS during exer-cise, even though serum DLIS concen-trations reportedly increase afterstrenuous physical activity (5). Ourstudy suggests that this increase inDLIS in serum after exercise could beat least partly ascribed to a decrease ofits removal via the kidney. Or possiblythe increase in circulating DLIS isproportional to the intensity of exer-cise. Further studies in which serumconcentration and urinary excretion ofDLIS are measured concomitantly after physical exercises ofdifferent inten-sity are necessary to confirm this hy-pothesis.References1. Valdea Jr It Endogenousdigoxin-likeimmunoreactive factors; impact on digoxinmeasurements and potential physiologicalimplications. Cbs Chem 1985;31:1525-.32.2. Soldin SJ. Digoxin-issues and contro-versies [Reviewl. Cbs Chem 1986;32:5-12.3. Clerico A, Ghione S, Balzan S, DelChicea MG. Digoxin-like immunoreactivesubstance: non-specific interference or anew hormone? J Nucl Med Allied Sci1984;28:297-301.4. DeWardenerHE, ClarksonEM. Conceptof natriuretic hormone. Physiol Rev1985;65:658-759.5. Valdes Jr R, Hagberg JM. Exercise-in-duced elevation of endogenous digoxin-likeimmunoactive factor in human serum [Ab-stractl. Clin Chem 1985;31:1008.6. Balzan S, Clerico A, Del Chicca MG, etal. Digoxin-like immunoreactivity in nor-mal human plasma and urine, as detectedby a solid-phaseradioimmunoasaay. ClinChem 1984;30:450-1.7. Clerico A, Del Chicca MG, Montreggi A,et al. Digoxin-like immunoreactivity in hu-man body fluids. J Nucl Med Allied Sci1985;29:305-12.8. Clerico A, Ghione S, Del Chicca MG,Balzan S. Problems in standardization ofdigitalis-like substance assaysby means ofcompetitive immunological methods [Let-torI. Clin Chem 1987;33:340-1.Aldo ClericoAntonio CambiMaria Grazia Del ChiccaLuigi CecchiniStefano GiacomC.N.R. Instit. ofClin. Physiol. andPostgrad. School ofSport Med.University of Pisa56100 Pisa, ItalyVariation among Instruments InInterference by Cephalosporin inthe Jaff#{233}ReactIon for CreatinlneTo the Editor:Cephalosporin antibiotics interferein the Jaff#{233}reaction for creatinine esti-mation, and different cephalosporinantibiotics interfere to different ex-tents (1).

Urinary excretion of digoxin-like immunoreactivity after physical exercise.

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