Renin and aldosterone concentrations in pregnant essential hypertensives - a prospective study

Serial blood samples were obtained throughout pregnancy from 11 women with essential hypertension (EHT). Seven were treated with labetalol (Trandate) and 4 with alpha -methyl dopa (Aldomet). Nine patients were well-controlled throughout pregnancy. Their mean plasma renin concentrations (PRC) followed the profile determined in 18 normal patients studied serially. They remained in the upper normal range until the last month, when both treatment groups showed a fall in PRC. Mean plasma aldosterone (ALD) also followed a normal profile until late gestation when it too showed a sharp fall. Of the two patients who developed superimposed PIH, one, who received labetalol, developed severe hypertension at 35 weeks, requiring delivery. Although PRC increased early in this pregnancy, ALD did not, remaining low throughout. Serum potassium [K+] measurements were also very low in this patient. The second patient only became hypertensive at 40 weeks and had PRC and ALD profiles resembling those in the successfully treated EHTs. There was a strong positive correlation throughout between serum potassium and ALD measurements (p less than 0.001) but none between PRC and ALD. This latter agrees with the known lack of correlation between PRC and ALD in normal pregnancy and may suggest that changes in electrolyte balance are more important stimuli to ALD secretion during pregnancy.