Changes in refractoriness of rabbit corpora lutea to a prostaglandin F2α analogue, alfaprostol, during pseudopregnancy

The responsiveness of rabbit corpus luteum to 200 mu g of the prostaglandin F-2 alpha (PGF(2 alpha)) analogue, alfaprostol, between Days 3 and 9 of pseudopregnancy was assessed by evaluating the decline in plasma progesterone after treatment with PGF(2 alpha) in 81 New Zealand White (NZW) rabbits. On Days 3-5, functional luteolysis was not observed. On Days 6, 7, and 8 of pseudopregnancy, the number of rabbits responsive to PGF(2 alpha) rose from 38% to 71% and 83%, respectively In the other cases, the effect of the PGF(2 alpha) analogue was transient as CL recovered in the following 2 or 3 days. By contrast, on Day 9 luteolysis was effective and persistent in all the animals. In rabbits treated on Day 9, progesterone decreased gradually from 10.6 +/- 0.7 within the first 6 h, but fell to 3.6 +/- 1.5 ng/mL (p < 0.02) 22 h after PGF(2 alpha) and to 0.2 +/- 0.1 ng/mL (p < 0.02) 24 h later.