Regional distribution of the angiotensinogens in human placentae

Angiotensinogen is the substrate for the enzyme renin. In addition to the well-characterized low molecular weight forms of angiotensinogen, a high molecular weight form (HMrA) comprises about 15 per cent of the total angiotensinogen in plasma of pregnant women. In the current study the different forms of angiotensinogen were quantitated in different regions of the placenta. The highest concentration of total angiotensinogen was found in the chorion laeve followed by the amnion. It was found that HMrA was the major form of angiotensinogen in all regions of the placenta, accounting for 72, 67, 63, and 59 per cent of the total angiotensinogen in the chorion laeve, chorion plate, amnion, and chorion frondosum, respectively. There was a significant correlation between the distribution of total renin and HMrA. This data in conjugation with previous data indicate that HMrA should be considered a significant component of the renin angiotensin system in the human pregnant state. It is suggested that HMrA may be a component of a tissue specific renin angiotensin system that occurs in the placenta.