Pre-partum changes in the plasma concentrations of progesterone, relaxin, prostaglandin F-2 alpha and 13,14-dihydro-15-keto prostaglandin F-2 alpha in meclofenamic acid-treated sows.

The pre-partum plasma concentrations of progesterone, relaxin, PGF-2 alpha and 13,14-dihydro-15-keto PGF-2 alpha (PGFM) were determined in 6 sows treated with meclofenamic acid (5.0 mg/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 less than 4.5 ng/ml at farrowing; (2) a surge in relaxin levels (greater than 100 ng/ml) by 2 days pre partum; and (3) sharp increases in the concentrations of PGF-2 alpha and PGFM within 24 h of parturition. Maximal concentrations of PGF-2 alpha (greater than 0.5 ng/ml) and PGFM (greater than 20.0 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.