Effects of a monoclonal antibody against progesterone, on embryo transport, development and implantation in laboratory mice

Abstract

A monoclonal antibody against progesterone (11P27) given on Day 2 of pregnancy interrupted pregnancy in BALB/c mice but not in BCF1 mice. The reason for this strain difference remains unclear, although it may involve discrimination by the recipient's immune system. The effects in BALB/c mice were reversed by progestin treatment. A dose of 5 nmol, which completely blocked implantation, had no significant effects on embryo transport and development on Day 4. A dose of 10 nmol did not increase the proportion of abnormal embryos, even though it accelerated tubal transport and increased embryo loss. No tubal retention was evident; most remaining embryos reached the uterus at the normal time. The transformation of morulae to blastocysts was only slightly delayed in 11P27-treated mice, and transfer experiments showed no decrease in embryo viability. The antibody appeared to act by blocking actions of endogenous progesterone on the uterus: uteri of 11P27-treated mice failed to develop a decidual cell reaction to intrauterine oil, and embryos from untreated donors failed to implant in 11P27-treated recipients. Antagonism of progesterone by antibody treatment prevented implantation in BALB/c mice apparently by actions on the uterus rather than on the embryo.