Abstract

It has been determined that a number of teratogens alter the osmotic environment around the rat embryo, an effect that is associated with abnormal fluid accumulation (and ultimately abnormality) in the embryo. At least one of these teratogens, trypan blue, changes lysosomal structure in the visceral yolk sac (VYS), an extra-embryonic membrane that envelops the extra-embryonic fluid compartment. The osmotic and ultrastructural effects are comparable in the in vivo and in vitro rat embryo. In the present study, the effects of other osmotic teratogens on VYS ultrastructure were investigated in rat whole embryo culture. Leupeptin (10 mug/ml) and E-64 (10 mug/ml) both caused a marked increase in the size of VYS lysosomes. Both chemicals inhibit cysteine proteinases, which are abundant in lysosomes. Suramin (750 mug/ml), an inhibitor of a number of lysosomal hydrolases, caused vacuolization of large areas of VYS cells. Ethylenethiourea (120 mug/ml) produced no marked ultrastructural changes, although the endocytotic apparatus of VYS cells appeared to have increased electron density, an effect that was also observed after treatment with the other teratogens. These results indicate that teratogens which alter embryonic osmotic balance also affect structures involved in endocytosis or lysosomal degradation of material by VYS cells.