Abstract Single stranded profiles of nuclear annulate lamellae were identified in giant cells of rat trophoblast from the day when the chorioallantoic placenta first becomes vascularized, viz., day 12 post coitum , until the day before term, viz., day 22. Cytoplasmic annulate lamellae were observed only in giant cells from placentas at day 12. Occasionally cytoplasmic annulate lamellae were found in parallel array. Often the lamellar membranes were continuous with both granular and agranular membranes of endoplasmic reticulum; they closely resembled doubled outer nuclear membrane. Nuclear annulate lamellae resembled doubled inner nuclear membrane; and often the two were found in continuity. In addition, at later gestational ages (17 and 22 days), nuclear lamellae often were related anatomically to the variety of nuclear inclusions which characterize giant trophoblast cells during late pregnancy. A possible relationship of annulate lamellae to the synthesis of DNA, RNA and protein is considered.
When the uterus of a rat is ligated so as to retain one placenta beyond parturition, trophoblast giant cells in the retained placenta involute within 2 days post partum. If, however, the partially delivered female either is allowed to suckle her litter or subsequently becomes pregnant, giant elements of trophoblast persist for as long as 6 days post partum. That such persistence is an action of progesterone has been demonstrated by injecting exogenous progesterone during the last several days of pregnancy, a procedure which both delays parturition and prolongs giant-cell persistence beyond the equivalent of term. Evidence is presented to suggest that: 1) during the terminal stages of a typical pregnancy, the number of giant cells normally decreases with concomitant attenuation and interruption of the giant-cell layer, and 2) the action of progesterone on the junctional zones of such placentae is to prolong the persistence of giant cells beyond a period of time equivalent to term. The possible significance of fixed giant-cell persistence with regard to the mechanisms of parturition is discussed.
Abstract A review of current knowledge of the unusual structure and several functions of the yolk‐sac membranes of common laboratory rodents, viz., rats, mice, hamsters, guinea pigs and gerbils, enables a better assessment of the significance of this maternofetal exchange system in the experimental production of congenital anomalies. The anatomy of both visceral and parietal walls of the rodent yolk‐sac placenta—specifically the anatomical relationships of each wall with maternal and with other fetal tissues—depends on the mode of origin and subsequent development of the yolk sac in these several species. Accordingly, the developmental biology of the rodent yolk sac is described. Since both fine structure and anatomical relationships also determine in large measure the functioning of the membrane as a whole in the absorption of selected materials either for intracellular digestion or for cellular translocation and transport to the developing embryo, the anatomy of the yolk sac is considered in detail. Similarly, since available evidence strongly suggests that teratogenic agents induce perturbations in the cellular mechanisms that control these several functions of the yolk‐sac placental system in the production of birth defects, additionally an account is given of the cell biology of the membrane, i.e., endocytosis and targeting/trafficking of materials either for digestion within the epithelium at the maternal surface of the visceral yolk sac or for translocation across the yolk‐sac membrane as a whole.
