A study of the temporal relationship between plasma high molecular weight angiotensinogen and the development of pregnancy-induced hypertension

In addition to the normally prevalent low molecular weight angiotensinogen (LMrA), significant quantities of a high molecular weight angiotensinogen (HMrA) are present in the human pregnant state. Previous studies have documented that 47% of women who develop pregnancy- induced hypertension (PIH) have a significantly elevated plasma HMrA/LMrA ratio. The purpose of this study is to establish whether or not the increase in the HMrA/LMrA ratio precedes the development of hypertension. Serial plasma samples were collected from a group of women throughout their pregnancy. High molecular weight angiotensinogen and LMrA levels in the samples from these women were determined. Fifteen of these women developed PIH. Seven women in the PIH group had a significantly elevated plasma HMrA/LMrA ratio. There was no consistent relationship between the elevation of the HMrA/LMrA ratio and the onset of hypertension. Three women had an elevated HMrA/LMrA ratio before the development of hypertension. In one woman the two events occurred simultaneously, and in three women the HMrA/LMrA ratio was elevated only after the development of hypertension. The current study shows that the development of hypertension during pregnancy is not the primary biologic signal for elevation of the plasma HMrA/LMrA ratio. Other parameters associated with fetal distress or abnormal development of placental circulatory systems must be involved in increasing the HMrA/LMrA ratio. It is proposed that the elevation of the HMrA/LMrA ratio is a mechanism by which the placental tissue specific renin-angiotensin system is attenuated.