EXTRACELLULAR AND INTRACELLULAR DEGRADATION OF COLLAGEN BY TROPHOBLAST GIANT-CELLS IN ACUTE FASTED MICE EXAMINED BY ELECTRON-MICROSCOPY

The fine structure of trophoblast giant cells and their interaction wi th collagen at the antimesometrial region on the 9th day of pregnancy was examined in fed and acute fasted mice, Collagen fibrils and filame ntous aggregates (disintegrating collagen fibrils) were observed in th e extracellular space, Three types of intracellular vacuoles containin g collagen fibrils were present: vacuole type A exhibited typical cros s-banded collagen immersed in finely granular electron-translucent mat erial; and vacuoles type B and C showed electron-opaque granular mater ial containing, respectively, faint cross-banded collagen and narrow c lear stripes often with faint periodicity, In fed animals vacuoles typ e B were absent and the others were less evident. Only fasted animals showed extracellular acid phosphatase activity on collagen fibrils, fi lamentous aggregates and confined regions of the extracellular space. Intracellular acid phosphatase activity was observed in vacuoles type B and in lysosomes. The results indicate that trophoblast giant cells are capable of breaking down extracellular collagen and also of intern alizing collagen for intracellular degradation, It is likely that thes e events are part of the process of invasion of the uterine wall, Howe ver, in fasted mice, collagen breakdown is more pronounced, and it may therefore contribute to the provision of amino acids and other nutrie nts for the undernourished fetus.