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.