A strategy used to protect the Ang-(1-7) against proteolytic degradation was proposed by Kluskens and coworkers [139] . Using the ability of prokaryotes to cyclize peptides, they synthesized a cyclic Ang-(1-7) derivative [thioetherbridged Ang-(1-7)] which presented an increased stability in homogenates of different organs and plasma and enhanced the Ang-(1-7) bioavailability in rats [139] . Furthermore, cyclized Ang-(1-7) induced a relaxation in precontracted aorta rings of rats which was blocked by the Ang-(1-7) receptor antagonist D-Pro 7 -Ang-(1-7), providing evidence that cyclized Ang-(1-7) also interacts with Mas [139] .