Possible significance of cells within intraluminal collagen masses in equine oviducts

In addition to the unique feature of retention of unfertilized ova, the oviducts of mares frequently contain large intraluminal masses with a fibrillar component and some cells. The aim of this study was to identify the cells and examine their relationship to the extracellular components of these masses. Intraluminal masses were examined both in situ and flushed from the oviducts. The nature of the contained cells and their relationship to the fibrils were examined by light microscopy and by transmission and scanning electron microscopy. In some mares the large masses distended the oviduct, but neither loss of the oviductal epithelium nor damage to this epithelium was seen. Electron microscopy verified that the principal cellular component was fibroblasts, and that the fibrils were type I collagen. Collagen masses collected shortly after ovulation frequently contained viable fibroblasts with collagen fibrils associated with their cell surfaces and with surface clefts. Although such collagen masses were present in pregnant and nonpregnant mares, masses with viable fibroblasts were chronologically associated with recent ovulation. It was concluded that connective tissue drawn into the oviduct at ovulation is retained, and collagen synthesis continues at least for a few days. Although the fibroblasts eventually disintegrate, the collagen remains and may in some cases aggregate within the oviductal lumen to the extent that oviductal transport and embryonic viability could be affected.