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HIGH CONCENTRATIONS OF INHIBIN IN THE ABDOMINAL FLUID AT THE TIME AFTER OVULATION IN MARES.
Nambo, Yasuo1, Nagata, Shun-ichi 2, Sasaki, Naoki 1, Yoshihara, Toyohiko 1, Watanabe, Gen 3, Groome, Nigel 4, Taya, Kazuyoshi 3, 1 2 3 4
ABSTRACT- Our previous study found that increases in circulating levels of immunoreactive (ir-) inhibin and inhibin pro-aC, which is the precursor of the inhibin a subunit, occurred at the time after spontaneous ovulation in mares (Nagaoka, K., et al., 1999, Am. J. Physiol. 277, E870-875). In addition, there were significant increases in plasma levels of ir-inhibin and inhibin pro-aC, but not estradiol following injection of equine follicular fluid into the abdominal cavity. To investigate the release of follicular fluid into the peritoneal cavity during ovulation in mares, twelve mares were given a single intravenous injection of 5000i.u. human chorionic gonadotrophin (hCG) when the growing follicles in the ovaries became >35 mm in diameter. Abdominal fluids were collected by abdominocentesis within at least 16 hours after ovulation (n=11) and during the various stage of the estrous cycle (n=27). Plasma samples were also collected at 1 hours-interval during ovulation (n=8). Concentrations of inhibin pro-aC, estradiol and progesterone were measured. Levels of inhibin pro-aC in the abdominal fluid were approximately 1000 times higher in post ovulatory period (1321.5 15716.9 pg/ml) than in non-ovulatory period (4.3-284.1 pg/ml). In post ovulatory period, levels of inhibin pro-aC were approximately 100 times higher in the abdominal fluid than in the plasma (33.5 95.7 pg/ml). Levels of estradiol in the abdominal fluid were only 3 times higher in post ovulatory period (9.1-52.7 pg/ml) than in non-ovulatory period (2.7-16.9 pg/ml). Plasma concentrations of inhibin increased during ovulation, followed by decline to basal value by at least 16 hours after ovulation. The present findings first demonstrated high levels of inhibin in the abdominal fluid after ovulation in mares, suggesting that most of the follicular fluid passes into peritoneal cavity in mares.
KEY WORDS: inhibin, ovulation, follicular fluid, mare