Investigation of the occurrence of a contraceptive tetrapeptide in hamster embryos.

The synthetic tetrapeptide H-Thr-Pro-Lys-OH, the extract of two-cell hamster embryos, and the oviductal contents devoid of embryos failed to show any in vivo antifertility activity. In addition, the tetrapeptide was not found in the biologic preparations of embryo extract and remaining oviductal contents. These findings are not in agreement with those of previous reports.