No abstract

Summary. The pre-partum plasma concentrations of progesterone, relaxin, PGF\x=req-\ 2\g=a\and 13,14-dihydro-15-keto PGF-2\g=a\(PGFM) were determined in 6 sows treated with meclofenamic acid (5\m=.\0mg/kg body wt daily, from Day 109 to Day 113 of pregnancy), and 2 sows which farrowed prematurely. The inhibition of PG synthesis with meclofenamic acid did not prevent either the decline in plasma progesterone or the release of relaxin. Three distinct stages in the progressive changes of the above hormones were apparent before parturition: (1) the gradual decline in the concentrations of progesterone from about 7 days pre partum to reach <4\m=.\5 ng/ml at farrowing; (2) a surge in relaxin levels (>100 ng/ml) by 2 daysprepartum; and (3) sharp increases in the concentrations of PGF-2\g=a\and PGFM within 24 h of parturition. Maximal concentrations of PGF-2\g=a\(>0\m=.\5 ng/ml) and PGFM (>20\m=.\0 ng/ml) occurred during farrowing. It is suggested that PG from an extra-ovarian source may not be responsible for initiating functional regression of the corpora lutea in the sow.