Prostaglandin F concentrations in the utero-ovarian venous plasma of the sow during the late luteal phase of the oestrous cycle

observations, together with the identification of PGF2\g=a\in the uterine venous plasma of anaesthetized ewes towards the end of the oestrous cycle (Bland, Horton & Poyser, 1971; McCracken et al. 1971), strongly suggest that PGF2\g=a\is the uterine luteolytic factor in sheep. This paper describes in detail the changes in PGF concentration in utero\p=m-\ovarian venous plasma of conscious ewes during the oestrous cycle. Polyvinyl catheters (1\m=.\5 mmo.d.)were inserted into the right and left utero\p=m-\ ovarian veins via uterine vein branches in two Merino ewes 10 and 11 days after oestrus. Utero\p=m-\ovarian venous samples were collected every 2-3 h from the day after surgery. Concentrations of PGF were measured by a radioimmunoassay (Thorburn, Nicol, Bassett, Shutt & Cox, 1972) using antisera raised in rabbits. Prostaglandin F2a and PGFlœ compete in an almost identical manner with [9-3H]PGF2lx over the analytical range (0-1-3-0 ng) of the assay. Prostaglandin E2 competes only weakly and no cross-reaction was observed with a wide range of steroids and lipids tested. Plasma samples (0-5 ml) were extracted with chloroform, then acidified and re-extracted. The second chloroform extracts were chromatographed on silica gel columns to separate the PG