Plasma renin activity in normal human pregnancy and in pregnancy-associated hypertension, with reference to cryoactivation.

1. Because hypertension is the central feature of pre-eclampsia, and because plasma renin activity is known to be elevated in normal pregnancy (with conflicting results published for pre-eclampsia), a prospective study of plasma renin activity was conducted in pregnancy, under conditions of a fixed sodium intake, in 178 initially normotensive volunteer subjects. Thirty of these women developed pregnancy-associated hypertension (pre-eclampsia) in the third trimester. 2. There was a significant elevation of plasma renin activity from the published values for non-pregnant women, throughout gestation in normotensive women. There was no significant difference, at any stage of gestation, between the values for normal women and those who developed pregnancy-associated hypertension. 3. The extent of cryoactivation of renin, produced by usual collection procedures, was investigated in a subgroup of the total population. It was highly significant and quite variable, but was similar in those who developed pregnancyassociated hypertension and in normal pregnant women. The mean increase in plasma renin concentration in maximally cryoactivated samples was 16-fold. 4. Neither measurement of peripheral plasma renin activity nor of cryoactivatable plasma renin concentration is of value in distinguishing between normal pregnant women and those destined for, or with pregnancy-associated, hypertension.