Immunoreactive rela.xin was shown to be present in pools of porcine follicular fluid collected from individual ovaries from cyclic and pregnant sows. In the cyclic animals, the highest relaxin level was obtained from ovaries containing active corpora lutes, but at no stage during the cycle did relaxin content of follicular fluid approach that found in ovaries of pregnant sows. Fractionation of follicular fluid on Sephadex C-SO revealed at least three immunoreactive relaxin peaks of differing molecular weight: >40,000, 20,000, and one corresponding to authentic relaxin (6300). Serum of pregnant sows when fractionated in a similar fashion contained more of the highest molecular weight immunoreactive relaxin while only ‘\‘20% of the immunoreactivity was associated with 6300 relaxin. Isolated ovarian follicles and follicular tissue released relaxin throughout prolonged periods in culture. Relaxin output in vitro was significantly higher for tissue obtained from pregnant than from nonpregnant sows. Examination of the relationship between steroid hormone and relaxin release revealed that follicle wall segments, washed free of follicular fluid, released both more relaxin and steroids than did intact follicles. Of the steroids examined, the pattern of relaxin most resembled that found for progesterone, which showed an increase after 48 h of culture as the tissue underwent spontaneous luteinization. The relationship between steroid hormone and relaxin biosynthesis was further studied in these cultures by the addition of inhibitors of steroid biosynthesis. Aminoglutethimide effectively reduced production of all steroids studied without significantly reducing the total production of relaxin over the culture period. Tniostane and androstriene 3, 17-dione were only partially effective in reducing steroidogenesis but caused a significant reduction in total relaxin production. Follicular tissue therefore synthesizes and secretes relaxin in vitro, but the cellular origin, the relationship with steroidogenesis, and the routes of release remain to be established.
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