Comparison of two protocols with a progesterone antagonist aglepristone (RU534) to induce parturition in bitches.

Parturition was induced in ten Beagle bitches by injecting them subcutaneously with 15 mg aglepristone kg-1 (Alizine) at day 58 of gestation and 24 h later and subsequently at 2 h intervals with either 0.08 mg alfaprostol kg-1 (Alfabedyl) (group 1; five bitches) or 0.15 iu oxytocin kg-1 (Ocytocine S) (group 2; five bitches). Blood samples were collected every 4 h until the end of parturition to assay plasma concentrations of progesterone, dihydro-keto prostaglandin F2 alpha (PGFM), oxytocin, prolactin and cortisol. Parturition occurred in all bitches. The mean time of onset of parturition for both groups was not significantly different (32.6 +/- 3.7 h for group 1 versus 31.6 +/- 3.6 h for group 2), although the mean expulsion time for bitches from group 2 (4.5 +/- 1.8 h) was significantly shorter than that of bitches in group 1 (9.1 +/- 2.0 h). At birth, 93% of the pups were alive in group 2 compared with 86% in group 1. Peripheral plasma concentrations of progesterone increased significantly after the administration of aglepristone, but direct or indirect luteolysis was not induced, and plasma concentrations of oxytocin or cortisol did not change during the first 24 h after administration of aglepristone. PGFM concentrations increased significantly after 4 h of aglepristone administration. During the first 20 h after aglepristone administration, prolactin concentrations increased significantly. At parturition, bitches in group 2, which had the shorter expulsion time of pups, were characterized by significantly higher concentrations of oxytocin and PGFM than bitches in group 1.