Allen C. Enders

The Endometrium of Delayed and Early Implantation

The length of gestation in a given species is generally proportional to the size of the young at birth and the relative maturity of the neonates. However, there are several variations in reproductive patterns that can extend the length of time from copulation to parturition. Delayed fertilization is a rare phenomenon found in a few species of bats (Wimsattet al 1966). Characteristically, sperm from a fall mating remain viable at the tubouterine junction until ovulation in the spring (Racey and Potts, 1970), and there is no retardation in the development of the zygote once fertilization has occurred. Conversely, in retarded development, now reported in at least two genera of bats, implantation occurs shortly after the blastocyst appears in the uterus, but formation of the placenta is slow, expecially the establishment of appropriate vascularization, and the early developmental stages of the embryo are retarded (Fleming, 1971; Bleier, 1975; Burns and Wallace, 1975; Wimsatt, 1975).

Galactosyltransferase Activity of the Microvillous Surface of Human Placental Syncytial Trophoblast

The syncytial trophoblast has previously been shown to have minimal intrasyncytial galactosyltransferase activity at term. The biochemical and autoradiographic study reported here shows that the microvillous surface of term human placental syncytial trophoblast has a galactosyltransferase activity capable of transferring 3H-galactose from uridine diphosphate-D-galactose-1-3H to trichloroacetic-acid precipitable, endogenous acceptors. This capability of resynthesizing cleaved galactose moieties in the glycocalyx, without dependence on cytoplasmically located galactosyltransferases, would allow for reinstatement of the original surface molecular configuration without requiring synthesis and insertion of a completely new membrane molecule. It is suggested that the surface galactosyltransferase might function to repair damage to syncytial trophoblast glycocalyx induced by the enzymes in maternal blood.

ELECTRON MICROSCOPY OF AN EARLY IMPLANTATION STAGE, WITH A POSTULATED MECHANISM OF IMPLANTATION.

Abstract An early attachment stage of implantation in the armadillo has been found and studied with the electron microscope. The trophoblast cells were seen to indent the uterine epithelium. The trophoblast cells at the region of attachment were cytologically similar to the other trophoblast cells free of association with the uterine epithelium. The microvilli of the two types of cells were intermingled, and in some places the distance between the two cell types was less than the average length of microvilli of the trophoblast in free areas. At one place the epithelial cells in contact with two of the trophoblast cells were disrupted at their apical ends. The presence of granular cellular contents from the uterine cells in the intercellular space was taken as an indication that the cell rupture might not be an induced artifact of fixation. It is suggested that once attachment has taken place, mechanical disruption of the uterine epithelium, especially by growth of the trophoblast, is a possible mechanism of initial penetration of the endometrium in this species, and that such a mechanism might be widespread.