Distribution of extracellular matrix components in the developing ruminantcorpus luteum: a wound repair hypothesis for luteinization

The aim of this study was to investigate corpus luteum development by visua lization of extracellular matrix proteins in the tissue at sequential stage s of the luteal phase. Corpora lutea were collected from oestrus-synchroniz ed sheep and from bovine material from an abattoir. The distributions of co llagen types I and IV, fibronectin and von Willebrand factor were determine d using immunohistology and semi-quantitative image analysis. During the po st-ovulatory period, a fibronectin- and von Willebrand factor-rich matrix o ccurred centrally, adjacent to the inner parenchymal surface, whereas durin g early luteal development a clear border of fibronectin separated the inne r parenchyma from the lumen. The inner parenchyma had abundant fibronectin initially, but the amount decreased as the rate of organ growth decreased. Over the same period, the amount of collagen type I first increased and the n decreased. Collagen type I and fibronectin were less abundant in other re gions of the parenchyma, and the general pattern was of slightly increasing amounts of collagen type I and decreasing amounts of fibronectin as luteal development proceeded. Ln contrast to earlier studies, only a small percen tage of large luteal cells was found to have an associated layer of collage n type IV (presumed basal lamina). It is concluded that luteal growth and m aturation require organized sequences of tissue remodelling. The central me shwork of fibronectin and von Willebrand factor and sequential deposition o f collagen type I and fibronectin are strongly reminiscent of events in gra nulation tissue. This indicates that luteinization may be best understood a s a wound repair-like process that succeeds the inflammation-like events of ovulation.