Studies of the physiological action of follistatin in the porcine ovary

Abstract

To investigate the physiological action of follistatin in the swine ovary a recombinant porcine follistatin (rpFS) with apparent molecular weights of 39, 46, 48, and 50 kDa was expressed and characterized. The rpFS crossreacted with antibodies against native porcine follistatin and with activin A. One rpFS isotype was purified by monoclonal antibody affinity chromatography (rp-305 a.a. FS). In porcine granulosa cell cultures, rp-305 a.a. FS suppressed estradiol-17 b accumulation (ED50 = 0.9 m g/ml) independent of activin. Gilts were vaccinated against rpFS to determine the effect of follistatin immunoneutralization on litter size or ovulation rate. In Experiment 1, forty-seven gilts were vaccinated four times with rpFS (FS n = 23) or with a control vaccine (CTL n = 24). The naturally matured, cycling gilts were bred and piglet numbers were recorded at farrowing. FS vaccination did not increase total litter size. However, grouping by low ( 1:400 n = 7) responses showed an increased litter size in gilts with a high titer (total piglets: FS high titer = 13.0 ± 0.8; FS low titer = 10.8 ± 0.6; CTL 11.4 ± 0.5; p = 0.08). In Experiment 2, sixty-nine gilts were vaccinated three times with rpFS (n = 35) or CTL (n = 34) vaccines. The gilts were induced and synchronized into estrus using PG600, PGF2a and boar exposure; cycling gilts received a fourth vaccination. Reproductive tracts were collected two weeks after the second observed estrus (FS n = 14, CTL n = 15). FS vaccination did not increase the number of corpora lutea (FS = 13.2 ± 0.5, CTL = 14.5 ± 0.7) or corpora albicantia (FS = 12.1 ± 1.9, CTL = 12.3 ± 2.0), but appeared to effect normal ovarian morphology increasing the number of blood-filled follicles and corpora lutea. In conclusion, rp-305 a.a. FS appears to negatively affect estradiol accumulation 'in vitro'. Vaccination against follistatin in naturally cycling gilts enhanced litter size. Follistatin vaccination of pharmacologically induced gilts did not increase ovulation rate, but biological effects were apparent suggesting that pharmacological induction of estrus may have confounded the follistatin vaccination treatment.