Endogenous digitalis-like activity in the newborn

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

Effect of fetal digoxin exposure (imprinting) on the sexual behavior of adult rats

1. Digoxin exposure of rat fetuses at the 15th, 17th and 19th day of pregnancy by treating the mother (with 9 microg digoxin altogether) caused alterations in the sexual behavior of adult rats (3-month-old males and six-month-old ovariectomized and hormone-treated females). 2. The number of active males was significantly higher in the treated group and ejaculation as well as multiple ejaculation occurred only here. Females also were more receptable after fetal digoxin treatment. It is known from the literature that long-term digoxin treatment in adult age influences (reduces) the male sexual activity in humans. In the rat, the opposite effect was observed after fetal treatment. 3. The experiments call attention to the prolonged effect of fetal digoxin exposure caused by the treatment of the mother.

Functional and structural properties of Na+/K(+)-ATPase enzyme in neonatal erythrocytes

BACKGROUND

The Na+/K(+)-pump is the main regulator enzyme of intracellular monovalent cation concentration. There are only limited data available concerning its structure and function in healthy neonates, in comparison with data available regarding its structure and function in children.

PATIENTS AND METHODS

Samples of 100 microL of anticoagulated blood were taken from 53 healthy neonates (age under 6th postnatal day, median age 3.5 days) and 61 healthy children (median age 12.4 months, range 6-36 months,). The Na+/K(+)-ATPase activity, its sensitivity to ouabain (a digoxin-analogue substance) and the expression of Na+/K(+) ATPase subunit isoforms were determined.

RESULTS

The enzyme activity (429.2 +/- 17.2 versus 295.5 +/- 10.2 U, P < 0 x 0.001) and I50 value for ouabain inhibition (1.50 +/- 0.10 versus 0.96 +/- 0.10 mumol L-1, P < 0.05) was higher in neonates. More alpha 1 subunits (relative density: 1.16 +/- 0.10 versus 0.75 +/- 0.03, P < 0.001) and higher alpha 1/ alpha 2 ratio (4.14 +/- 0.21 versus 2.02 +/- 0.16, P < 0.01) were detected.

CONCLUSION

This is the first study demonstrating changes of Na+/K(+) -ATPase molecules not only in enzyme activity, but also on protein level. Our results might contribute to the understanding of the resistance of neonatal cell membranes toward the pharmacodynamic actions of cardiac glycosides.

Fetal digoxin treatment enhances the binding capacity of thymic glucocorticoid receptors in adult female rats

1. Hormonal imprinting is provoked in the perinatal critical period in the presence of the appropriate hormone or molecules similar to it. As a consequence of hormonal imprinting, the developing receptor finishes its maturation normally (in the presence of the adequate hormone) or abnormally (under the effect of foreign molecules that are able to bind to the receptor). 2. Digoxin--which has a steroid character--caused faulty imprinting by treatments at the 15th, 17th and 20th days of pregnancy. In the adult (3-month-old) animals, the density of thymic glucocorticoid receptors was significantly elevated, whereas the density of uterine estrogen receptors was not, without any change in receptor affinity. 3. The experiments call attention to the steroid receptor imprinting effect of fetal digoxin treatment that must be considered in regard to this treatment at this period and later in regard steroid treatments.

Different methods for measuring endogenous digitalis-like factor(s)

It is well recognized that one of the difficulties in the search for endogenous ligand(s) with digitalis-like properties (endogenous digitalis-like factor(s), EDLF) in mammals has been the lack of a unique, specific method for the accurate measurement of EDLF. Using C18 solid-phase extracts of plasma from normal adults and various patient groups, and purified extracts from umbilical cord plasma by affinity resin chromatography and HPLC, different methods to measure EDLF were evaluated. These were: (a) a human placenta radioreceptor assay (RRA) developed on the premise that competition for cardiac glycoside receptors was an absolute requirement for EDLF; (b) the inhibition of 86Rb uptake in human erythrocytes to estimate the potassium transport by the sodium pump; (c) an enzyme immunoassay specific for ouabain recently introduced in the market (DuPont Ouabain EIA Reagent Pack). The human placenta RRA was found to have the same ease of application as immunoassay, but could have major advantages in detecting active molecules, being "biologically more meaningful". Ouabain immunoreactivity correlated with EDLF values obtained by RRA, but in some instances the two assays were completely unrelated. Moreover, the high specificity of the DuPont antibody for ouabain (< 3% cross reactivity with digoxin) could be disadvantageous to detect EDLF not strictly resembling ouabain. The 86Rb uptake inhibition method correlated with RRA for EDLF purified by HPLC. It tested the complete enzymatic cycle and could therefore better reflect the in-vivo inhibitory activity of EDLF. However, it appeared not suitable for the routine EDLF evaluation in clinical studies since it was susceptible to sample osmolarity and required daily isolation of human erythrocytes possibly from the same donor. Results of the present study demonstrate that every assay has its limitations, and would suggest the use of multiple assays for EDLF detection.