PARENT SESSION
Pregnancy and Parturition

INHIBIN AND ACTIVIN SECRETION IN EQUINE FETO-PLACENTAL UNIT.

Tanaka, Yumiko¹, Nagamine, Natsuko^1,2, Taniyama, Hiroyuki³, Tsunoda, Nobuo², Nambo, Yasuo⁴, Nagata, Shun-ichi⁵, Watanabe, Gen¹, Taya, Kazuyoshi¹, ^{1 2 3 4 5}

ABSTRACT- Secretions of inhibin and activin from equine placenta, uterus and fetal gonads were investigated during pregnancy in mares. Concentrations of immunoreactive (ir-) inhibin, inhibin pro-C, inhibin A and activin A in fetal and maternal plasma and these organs were measured by RIA and ELISA. Immunolocalizations of inhibin-, A- and B-subunits in feto-placental unit were also investigated using by ABC method. Plasma concentrations of ir-inhibin, inhibin pro-C and inhibin A in fetuses were dramatically higher than those in dams. Contents of ir-inhibin, inhibin pro-C and inhibin A in the fetal gonads were much higher than those of the placenta and uterus. On the other hand, large amounts of activin A were detectable in the placenta and the uterus (especially in the uterus) but not the fetal gonads. All three inhibin subunits (, A and B) were localized in interstitial cells of the fetal gonads of both sexes and Sertoli cells of fetal testis. Immunostainings for both inhibin A- and B-subunits were observed in the uterus, whereas only inhibin B-subunit was localized in the placenta. No positive stainings for inhibin -subunit was detected in both the placenta and uterus. These results suggest that fetal gonads mainly secrete inhibins, and the placenta and uterus mainly produce activins. These inhibins and activins in feto-placental unit may play some important roles for fetal growth.

KEY WORDS: inhibin, activin, feto-placental unit, horse