Ovarian prorenin-renin-angiotensin system.

Renin is classically considered to be an enzyme that is synthesized by the kidneys and secreted into the circulation where it affects angiotensin production. We review here recent evidence that suggests the existence of an extra-renal renin system, the ovarian prorenin-renin-angiotensin system, which may be linked to reproductive function. Prorenin, the inactive form of the enzyme renin, is present in the fluid of mature human ovarian follicles in extremely high concentrations; however, only 1 per cent of the renin in follicular fluid is in the active form. Plasma prorenin increases about 2-fold at midmenstrual cycle at the time of the LH surge, and the peak of prorenin is sustained for about 2 days. No change in plasma active renin levels occurs at this time. Administration of hCG to women whose ovaries have been stimulated with gonadotropins results in much higher plasma prorenin levels and the height of prorenin response is directly related to the number of mature follicles. Plasma prorenin also increases 10-fold during the early stages of pregnancy. It begins to rise on days 8 to 12 after embryo transfer, in parallel with the rise in endogenous hCG. The ovaries are the apparent source of the increase in plasma prorenin in early pregnancy since no such increase in prorenin occurred in a woman with ovarian failure who conceived after receiving a donor egg. These results suggest that prorenin is synthesized and secreted by the mature ovarian follicle and by the corpus luteum in response to LH/hCG. They also suggest that an ovarian renin system exists that is regulated by changes in prorenin.(ABSTRACT TRUNCATED AT 250 WORDS)