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

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Abstract
Summary. 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-2α (25 μg/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 < 0·01). A shorter infusion (25 μg/h for 3 h) or a lower hourly dose rate (12·5 μg/h for 6 h) of PGF-2α was ineffectual, suggesting that a dose/duration regimen exists for PGF-2α-mediated luteolysis. PGE-2 (25 μg/h for 6 h) or sodium arachidonate (667 μg/h for 6 h) did not significantly affect luteal function. Of the PGF-2α metabolites examined, 13,14-dihydro-PGF-2α was the most effective: it was approximately 4-fold more potent as a luteolysin than PGF-2α since functional regression occurred with infusion of 6·25 μg/h for 6 h. These data illustrate that systemic infusion of PGF-2α is capable of inducing luteolysis in the rabbit. The metabolite 13,14-dihydro-PGF-2α may also be involved luteolytically in this species.