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

Abstract

In addition to the normally prevalent low molecular weight angiotensinogen (LM rA), significant quantities of a high molecular weight angiotensinogen (HM rA) 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 HM rA/LM rA ratio. The purpose of this study is to establish whether or not the increase in the HM rA/LM rA ratio precedes the development of hypertension. Serial plasma samples were collected from a group of women throughout their pregnancy. High molecular weight angiotensinogen and LM rA 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 HM rA/LM rA ratio. There was no consistent relationship between the elevation of the HM rA/LM rA ratio and the onset of hypertension. Three women had an elevated HM rA/LM rA ratio before the development of hypertension. In one woman the two events occurred simultaneously, and in three women the HM rA/LM rA 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 HM rA/LM rA ratio. Other parameters associated with fetal distress or abnormal development of placental circulatory systems must be involved in increasing the HM rA/LM rA ratio. It is proposed that the elevation of the HM rA/LM rA ratio is a mechanism by which the placental tissue specific renin-angiotensin system is attenuated.