Increased Sodium-Lithium Countertransport in Erythrocytes of Pregnant Women

Two groups of investigators have shown that erythrocyte sodium-lithium countertransport is higher in patients with essential hypertension than in normotensive individuals. The present authors have investigated sodium-lithium countertransport in normal and hypertensive pregnant women to ascertain whether the relation between cation flux in these two groups of subjects is similar to the observed differences between normal and hypertensive nonpregnant women. They reasoned that if countertransport in women with pregnancy-induced hypertension differs from that in normal pregnant women, prospective measurement of cation flux might lead to a useful technique for identifying incipient pregnancy-induced hypertension.The authors measured sodium-lithium countertrans-port in erythrocytes of the following subjects24 normotensive nonpregnant women, 39 normal pregnant women, nine women with pregnancy-induced hypertension, eight neonates (cord blood), and 27 of the mothers at various intervals after delivery.Mean sodium-lithium countertransport was higher both in normotensive pregnant women and in subjects with pregnancy-induced hypertension than in normotensive nonpregnant women. Mean countertransport for the non-pregnant women was the same as the mean (± SE) of 0.24 ± 0.06 found in normotensive women by other investigators. Elevations during pregnancy above the mean for nonpregnant women were statistically significant (P < 0.001) in both normotensive and hypertensive gravidas, but the two groups of pregnant women did not differ from each other.The authors found no effect of parity on countertransport in the pregnant women. Two of the normal gravidas were carrying twin fetuses, and their countertransport values were 0.32 and 0.59. Two women whose current pregnancies were normal had pregnancy-induced hypertension during a previous pregnancy. Their countertransport values in the current pregnancies were 0.27 and 0.44, respectively.To evaluate the pattern of rise in countertransport during pregnancy, the authors compared values from observations made at midpregnancy with those from observations made near term. Since there was no difference in mean countertransport between normal and hypertensive pregnant women, they combined the values of these two groups for this portion of the analysis. Mean countertransport in nine women studied between the 11 th and the 28th weeks of gestation was higher than in 24 nonpregnant controls (0.31 ± 0.02 vs. 0.24 ± 0.01, P < 0.005) but lower