Digoxin- and Digitoxin-Like Immunoreactive Substances in Amniotic Fluid, Cord Blood, and Serum of Neonates

Abstract

ABSTRAm. Using four different digoxin kits, it was disclosed that the majority of various samples including amniotic fluid, cord blood, and serum from neonates contained substantial levels of digoxin-like immunoreactive substance. The differences in data seemed to be due to the range of epitopes which are recognized by antidigoxin antiserum. The day-to-day studies on sera serially obtained from infants at birth to 48 days old revealed that the level of the substance (0.31 f 0.12 ng/ml) in sera of the l-dayold neonates rapidly declined to the level of 0.1 ng/ml by the 2nd postnatal wk and thereafter gradually declined. The immunological specificity and accuracy of the detection of digoxin-like immunoreactive substance was confirmed by a sample dilution test, a recovery test for standard digoxin, and an absorption test with antidigoxin antiserum. The amniotic fluid and cord blood also contained Recent reports (1-3) renewed our attention toward the falsepositive digoxin measurements in the plasma of premature infants (4). From the clinical viewpoint, these observations raise some important questions. The first question is whether the falsepositive digoxin measurement really indicates the presence of a DLIS which leads to an erroneous judgment about the level of digoxin in monitoring of neonatal samples. The second question is whether there is any similarity in biochemical specificity between DLIS and the so-called "ouabain-like substances" detected in other organs or body fluids (5-13). It seems that previous reports (1-3) have not yet provided substantial evidence for their conclusion that the substance is not a product of technical or nonimmunological false positivity. Therefore, in this communication, we tried to confirm the previous findings using Received September 6, 1984; accepted August 19, 1985. Address for correspondence Hiroyoshi Ebara, M.D., Department of Pediatrics, Gunma University School of Medicine, 3-39-22 Showa-machi, Maebashi-shi, Gunma-ken, Japan. amniotic fluid, cord blood, and serum specimen from neonates and also to evaluate immunological specificity of the reaction and presence of a DTLIS. MATERIALS AND METHODSThirty-one amniotic fluid and 53 cord blood samples were obtained from mothers who had not received any digitalis glycosides during pregnancy and labor. One hundred eleven sera were also obtained from 23 neonates over 35-wk gestational age who were delivered from healthy mothers who had not been on digitalis therapy. The mean and range of birth weight of the neonates were 3264 g and 20 16-4420 g, respectively. The investigation was approved by the ethical committee of the hospital and informed parental consent was obtained for blood sampling. All samples were stored at -20" C in separate small quantities to avoid unnecessary freezing and thawing, and analyzed at various intervals, always within 30 days of collection.For the detection of DLIS, one EIA kit and three RIA kits available in Japan were used: kit A (Markit Digoxin, DainipponSeiyaku, Osaka, Japan); kit B (Amerlex Digoxin RIA k...

Digoxin-like immunoreactive substance in serum of preterm and full-term neonates

“…Graves et al [5], Beyers et al [2] and Ebara et al [3] have noticed the presence of DLIS in serum of pregnant women in their third trimester, in their amniotic fluid as well as in their placental extracts, suggesting a maternal origin. Graves et al [5] noticed a disappearance of DLIS from serum of mothers 24 h after parturition, suggesting a half-life for this substance of 6 h or less.…”

Endogenous inotropic factor‐induced endothelium‐dependent relaxation of vascular smooth muscle

“…Hallaq & Haupert (1989) have also isolated an endogenous substance which stimulates cardiac contractility. The isolation of endogenous substances from plasma of volume-expanded dogs (Gruber et al, 1989), human plasma (Kelly et al, 1985;Balzan et al, 1986), human urine (Goto et al, 1993) and other tissues (Ebara et al, 1986) has also been reported. These substances or factors were demonstrated to share some pharmacological and immunological properties with ouabain (Hamlyn et al, 1991) or digoxin (Haddy & Pamnani, 1983;Haddy, 1987).…”

Positive inotropic effect of porcine left ventricular extract on canine ventricular muscle

“…Even though many laboratories have been able to demonstrate the presence of digitalis-like substance(s) either immunologically or biochemically, the functional characterization of positive inotropism was not done in these studies (Gruber et al, 1980;Kelly et al, 1985;Balzan et al, 1986;Ebara et al, 1986). The crude extract obtained in our laboratory from porcine ventricle was consistently inotropic in guinea-pig isolated hearts (Khatter et al, 1986).…”

“…has been attempted by many laboratories (Gruber et al, 1980;Kelly et al, 1985;Balzan et al, 1986, Ebara et al, 1986). In our laboratory, we isolated a crude fraction from porcine left ventricle, after extraction of lipids, chromatographic separation and desalting (Khatter et al, 1986).…”