Digoxin-Like Immunoreactivity in Early Infantile Death

The aim of this study was to determine if the level of digoxin-like immunoreactivity in post-mortem sera obtained from infants differs according to the cause of death and if the level is related to age, post-mortem interval, cardiac pathology or adrenal weight. Twelve infants whose deaths were attributed to sudden infant death syndrome (SIDS), and 11 infants who died from other causes, had blood sampled between 3 to 53 hours post-mortem from their right atrial cavity. Digoxin-like immunoreactivity was measured, using a specific and sensitive digoxin radioimmunoassay, and was detected in 7 of the infants who died of SIDS and 7 of those who died from other causes. The highest levels were seen in two patients who died from meningococcal sepsis and haemorrhage, hyperpyrexia and encephalopathy syndrome, respectively. No correlation was detected between the digoxin-like immunoreactivity level, gender, age at death, post-mortem interval or cardiac pathology. Digoxin-like immunoreactivity levels correlated with adrenal weight. It is concluded that digoxin-like immunoreactivity is frequently found in infant sera, but levels are not specific to and are no higher in SIDS infants than infants dying of other conditions.

Disposable-column radioimmunoassay for serum digoxin with less interference from metabolites and endogenous digitalis-like factors.

A preparative extraction step using disposable C18 low-pressure chromatography columns greatly improved the specificity of a commercially prepared digoxin radioimmunoassay (RIA). Elution solvents were isopropanol/water (15/85 by vol), which extracted most immunoreactive digitalis-like factors and metabolites, and methanol, which extracted digoxin for RIA. Many different digoxin RIA kits could be used. The coefficients of variation for replicates and duplicates were 4.6% and 5.2%. Analytical recoveries of digoxin standards in serum of 1.0, 0.5, and 0.1 microgram/L were 96%, 95%, and 88%, respectively. Serum digoxin was assayed by this method in 200 patients, 47 of whom were studied by HPLC-RIA. Values correlated better with "true digoxin" by HPLC-RIA (r = 0.93) than did values found by direct assay (r = 0.63). The mean for the isopropanol fraction as a percentage of the mean direct RIA value was higher for the 21 dialysis-dependent patients than was that found for the 179 nondialysis patients (P less than 0.004). The method is suggested as being most useful when metabolites or digitalis-like factors are known to be often high and values for digoxin are disproportionate to the dose.

Effect of High Sodium Intake on Tissue Distribution of Endogenous Digitalis-Like Material in the Rat

1. The effect of a high sodium intake on the endogenous digitalis-like activity of several tissues was determined, after extraction, by digoxin radioimmunoassay in rats. 2. The high sodium intake increased the digitalis-like activity in serum but not in adrenals, brain or heart.