Although the kidney is a major source of prorenin, the precursor of renin, there are extrarenal sources for plasma prorenin that have not been identified. The selective increase in plasma prorenin at the time of ovulation suggested that one of these sources might be the ovary. Prorenin was therefore measured in fluid aspirated from 18 ovarian follicles and in plasma collected from three women who were undergoing in vitro fertilization. The follicular fluid contained high concentrations of prorenin that were approximately 12 times higher than plasma prorenin. The prorenin from follicular fluid was immunochemically identical to kidney and plasma prorenin. Thus, the ovary is a likely source for the ovulatory peak of plasma prorenin.

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