Digoxin-like immunoreactive substance and sodium-potassium-adenosine triphosphatase inhibition in normal pregnancy: a longitudinal study.

OBJECTIVE

To measure the levels of digoxin-like immunoreactive substance and digitalis-like factor bioactivity as manifested by sodium-potassium-adenosine triphosphatase (ATPase) inhibition throughout pregnancy.

METHODS

Serum samples were collected from primigravidas in early (15 +/- 1.8 weeks), mid (26 +/- 1.2 weeks), and late (36 +/- 1.1 weeks) gestation, as well as at 6 +/- 1.1 weeks postpartum (mean +/- standard error). Digoxin-like immunoreactive substance levels were determined by radioimmunoassay and digitalis-like factor bioactivity was determined by inhibition of ATPase. Data were analyzed by means of repeated measures analysis of variance.

RESULTS

In 41 women with normal pregnancy outcomes, levels of digoxin-like immunoreactive substance rose progressively and significantly (P < .001) throughout pregnancy and returned to normal levels postpartum. Inhibition of ATPase activity also rose significantly (P < .004), but not as dramatically, during pregnancy and remained elevated 6 weeks postpartum.

CONCLUSION

Although digoxin-like immunoreactive substance levels rise in pregnancy, functional digitalis-like factor activity, as manifested by inhibition of ATPase, does not parallel this rise strictly, implying that digoxin-like immunoreactive substance receptors may be reset during normal pregnancy. The enhanced cardiac performance that occurs in normal pregnancy may be mediated in part by increased digitalis-like factor activity.