Indomethacin delays zona-shedding and implantation in the ovariectomized progesterone-treated hamster

Pregnant hamsters were ovariectomized on Day 2 (Day 1 = sperm positive) and given progesterone replacement therapy daily (200 microgram sc in sesame oil). Either 2 or 4 mg indomethacin (Indo) given on Day 3 and early Day 4 delayed shedding of the zona pellucida and the onset of implantation on Day 4. One mg Indo administered on Day 3 was only partially effective. By Day 5, approximately half of the hamsters receiving either 2 or 4 mg Indo exhibited implantation sites whereas all controls and hamsters receiving 1 mg Indo had sites. At the dosages used, estradiol cypionate, histamine, prostacyclin and prostaglandin E2 did not overcome the effects of Indo. The results indicate that Indo interferes with zona shedding and implantation of blastocysts in the ovariectomized-progesterone treated hamster.