Significance of maternal uterine proteins in the establishment of pregnancy.

Mammalian embryonic development depends on extrinsic support by the maternal organism. During the preimplantation period the growing blastocyst needs favourable environmental conditions, which are provided by endometrial transformations and secretion. The macromolecular composition of uterine secretion at different times before implantation is characterized by a spectrum of protein patterns which change daily. In an attempt to shed light on the significance of the uterine secretion proteins, particularly uteroglobin in the rabbit, in the establishment of early pregnancy, analyses are reported which demonstrate the origin and endocrine control of the synthesis and release of these proteins. In a comparative study of blastocyst development in vivo and in vitro the significance and consequences of asynchrony between the embryonic and maternal reproductive phases are investigated. Particular attention is drawn to uterine influences on the rabbit blastocyst coverings, and how embryonic development can be retarded by abnormal structural transformation of the zona pellucida and the mucin coat. Finally, the covenient experimental systems of pseudopregnancy and of delayed uterine secretion in the rabbit permit an approach the question of whether the uterine macromolecular components constitute a maternal response to the presence of the as yet unimplanted blastocyst.