Digitalis-like factor and digoxin-like immunoreactive factor in diabetic women with preeclampsia, transient hypertension of pregnancy, and normotensive pregnancy

An endogenous sodium pump inhibitor, or digitalis-like factor (DLF), has been postulated to mediate essential hypertension. It may also play a role in preeclampsia. However, studies of this factor in hypertensive pregnancy have not provided consistent findings. Part of this may be due to the absence of subclassification of pregnant women with pregnancy-induced hypertension (PIH) when assessing these parameters. In this study we explored serum DLF and digoxin-like immunoreactive factor (DLIF) in insulin-dependent diabetic (IDDM) women with normotensive pregnancies or PIH, comparing them to each other and to nondiabetic pregnant women. Our results demonstrated that nondiabetic women with preeclampsia (PE, PIH with proteinuria) had significantly increased serum DLF and DLIF compared to normotensive pregnant women (NL BP). Women with transient hypertension of pregnancy (THP, PIH without proteinuria) had intermediate values (DLF. NL BP: 3.3 ± 0.6, THP: 4.8 ± 1.1, PE: 7.6 ± 1.3% inhibition [Na,K]-ATPase, P< .05 ANOVA; DLIF. NL BP: 0.22 ± 0.02, THP: 0.28 ± 0.03, PE: 0.35 ± 0.02 ng digoxin equivalents/mL, P< .05 ANOVA). Pregnant normotensive IDDM women had significantly higher serum DLF and DLIF activity than their nondiabetic counterparts (DLF. non-IDDM NL BP: 3.3 ± 0.06 v IDDM NL BP: 8.8 ± 1.2% inhibition [Na,K]-ATPase, P = .0008; DLIF. non-IDDM NL BP: 0.22 ± 0.02 v IDDM NL BP: 0.31 ± 0.02 ng digoxin equivalents/mL, P = .005). However, in the IDDM pregnant women, serum levels of DLF and DLIF were not significantly increased further with PIH (DLF. NL BP: 8.8 ± 1.2, THP: 6.9 ± 2.8, PE: 6.1 ± 1.4% inhibition [Na,K]ATPase, P = NS ANOVA; DLIF. NL BP: 0.31 ± 0.02, THP: 0.36 ± 0.07, PE: 0.38 ± 0.04 ng digoxin equivalents/mL, P = NS ANOVA). These results suggest that in non-diabetic pregnant women, DLF and DLIF are only significantly increased in preeclampsia. Moreover, in IDDM pregnant women, the presence of increased DLF and DLIF in normotensive subjects and the absence of a significant further increase in subjects with PIH suggests that hypertension in these women may differ mechanistically from PIH in nondiabetic women. Lastly, inclusion or exclusion of diabetic pregnant women can lead to different results for DLF in PIH.