High concentrations of immunoreactive renin, prorenin and enzymatically-active renin in human ovarian follicular fluid

Prorenin (enzymatically inactive) and renin (active) were measured by radioimmunoassay, using monoclonal antibodies reacting either with both prorenin and renin or with renin alone, in pre-ovulatory follicular fluid (FF) from women in an in-vitro fertilization programme who were stimulated with human menopausal/human chorionic gonadotrophin. The concentration of prorenin in FF was 40 times higher than in plasma taken at the time of FF collection; renin in FF was 10 times higher. The plasma concentration of prorenin, but not of renin, in these women was higher than in non-stimulated women in the late follicular phase of the menstrual cycle. The concentration of reninsubstrate and angiotensin-converting enzyme in FF was 60% of that in plasma. Contamination of blood, which may occur at the time of FF collection, was less than 5%. Prorenin in FF was irreversibly converted into renin after adding trypsin or by endogenous serine protease, using procedures that also cause conversion of prorenin in plasma. These results support the hypothesis that the increased plasma level of prorenin in women whose ovulation is stimulated for the collection of oocytes has originated from the ovary and is under gonadotrophic control. This may also be true for the increase of plasma prorenin that has been observed in non-stimulated women during the luteal phase of the cycle and in early pregnancy.