Assessment of the luteolytic potency of various prostaglandins in the pseudopregnant rabbit.

The ability of systemic infusion of arachidonic acid and various prostaglandin (PG) compounds to induce luteolysis was examined in the Day 9 pseudopregnant rabbit. Administration of PGF-2 alpha (25 microgram/h for 6 h) elicited a decline in plasma progesterone from mean +/- s.e.m. pretreatment levels of 8.83 +/- 0.54 to 0.54 +/- 0.05 ng/ml on the following day (P less than 0.01). A shorter infusion (25 microgram/h for 3 h) or a lower hourly dose rate (12.5 microgram/h for 6 h) of PGF-2 alpha was ineffectual, suggesting that a dose/duration regimen exists for PGF-2 alpha-mediated luteolysis. PGE-2 (25 microgram/h for 6 h) or sodium arachidonate (667 microgram/h for 6 h) did not significantly affect luteal function. Of the PGF-2 alpha metabolites examined, 13,14-dihydro-PGF-2 alpha was the most effective: it was approximately 4-fold more potent as a luteolysin than PGF-2 alpha since functional regression occurred with infusion of 6.25 microgram/h for 6 h. These data illustrate that systemic infusion of PGF-2 alpha is capable of inducing luteolysis in the rabbit. The metabolite 13,14-dihydro-PGF-2 alpha may also be involved luteolytically in this species.