| Abstract: | The cytochemistry and ultrastructure of the lysosomal area of the rat's yolk sac placenta was studied at various stages of development. The lysosomal area, located at the apical end of the yolk sac epithelial cell between the microvillous border and the nucleus, consisted of dense bodies that persisted from day 10 of pregnancy through gestation and multivesicular bodies that are present only through day 12. Acid phosphatase activity was restricted to the dense material and to the membranes of this area. Two types of pinocytotic vesicles were present in all stages of development. One was a tubular structure containing dense material and the other, a saccular, clear structure containing a “fuzz-lining” and membrane remnants. Possible relationships between the pinocytotic vesicles and the dense and multi-vesicular bodies were considered. The injection of Triton WR-1339 on day 11 of pregnancy resulted in a vacuolation of the dense and multivesicular bodies. This vacuolation began 15 minutes after injection and maximum effect was reached within 12--24 hours. A reorganization of the lysosome area occurred on days 15--16 in those animals in which pregnancy continued to term. This reorganization consisted of an increase in the dense material within the vacuoles and a reduction in vacuole size. The vacuoles remained distended in those animals in which death and resorption of the fetus occurred. The first cellular changes associated with death occurred between 48--60 hours post-injection. The microvilli became shorter, thicker and reduced in number; the pinocytotic vesicles disappeared from the cell surface; the endoplasmic reticulum became dilated and vesiculated; and vesicles were formed from the cristae of the mitochondria. With the injection regimen used in this study, 25% of the litters were resorbed while the remainder of the pregnant rats delivered viable fetuses at term. |
