OVARIAN AND UTERINE RENIN-ANGIOTENSIN SYS TEM IN MAMMALS

The circulating renin-angiotensin system (RAS) participates in the reg ulation of blood pressure and electrolyte metabolism. Renin, a proteol ytic enzyme, synthesized in the kidney from its biological precursor, prorenin, cleaves its substrate angiotensinogen in the blood to form t he active octapeptide, angiotensin II (All). All the RAS components ar e present in the reproductive system of mammals. During pregnancy, the level of prorenin increases in the plasma. The ovary is the source of this prorenin during early pregnancy and maternal decidua later on. D uring the menstrual cycle, the thecal of preovulatory follicles synthe size prorenin, renin and All. Thecal renin systhesis is controlled by LH/hCG as demonstrated in vivo and in vitro in the rabbit. Ovarian ren in seems to be identical to kidney renin. Prorenin appears to be the m ajor secretory product rather than renin, which remains intracellular. A T2-type angiotensin II-receptors are expressed in the rat on follic ular granulosa cells and could be down-regulated by FSH. The bovine th ecal cells also express AT2-receptors, up-regulated by LH. These data are consistent with an autrocrine or paracrine role for ovarian RAS. I t has been implicated in neovascularization of the follicle and regula tion of steroidogenesis by increasing the androgen/estrogen ratio, an index of follicular atresia.