Identification of components of the intrafollicular bradykinin-producing system in the porcine ovary?

As a step in elucidating the biological role of plasma kallikrein (PK) pres ent in the follicular fluid of mammalian ovaries, we examined pig ovary flu id to determine its constituent activators and substrates. Using the inacti ve precursor form of plasma kallikrein (prePK) as a substrate, we purified an enzyme capable of activating this protein. The prePK-activating enzyme w as shown to be the active enzyme blood coagulation factor,XIIa. We also iso lated high molecular weight kininogen (HMW-K) from the same fluid. incubati on of HMW-K with the ovarian follicular fluid PK resulted in the production of the nanopeptide bradykinin (BK). Expression of prePK, blood coagulation factor XIII and HMW-K was examined by Northern blot analysis using ovary a nd liver poly(A)(+) RNA. All these transcripts were found in the liver, but none were found in the ovary. In addition, it was found that BK levels in the fluid derived from the small follicles were approximately 6 times highe r than those from medium and large follicles. These results demonstrate the presence of a BK-producing system in the ovarian follicles and suggest the physiological importance of this peptide hormone in the early stages of fo llicular development and at ovulation.