Coincidence of embryonic growth and uterine protein in the ferret.

The protein content of fluids isolated from the lumen of the uterus of the ferret was correlated with growth of the pre-implantation embryo. Similar observations were made with mink for comparative purposes. Tt is concluded that in the ferret: Protein content rises coincidentally with blastocyst expansion, becoming especially high when the embryo is implanting. The proteins present early in the period are of types that diffuse easily in electrophoresis; they become more like those of serum near the time of implantation. There is no evidence of an embryonic diapause. Mitotic activity in cells of the blastocyst is maintained at a high rate (about 5 %). The prolonged pre-implantation period results from a relatively long mitotic duration in blastocyst cells (80+ min). The protein content found during the pre-blastocyst period is similar to that of mink uterine fluids collected during the period of embryonic diapause. This observation provides additional circumstantial evidence that the embryonic diapause accompanying delayed implantation is related to limited protein availability.