Identification and measurement of collagen in the bovine corpus luteum and its relationship with ascorbic acid and tissue development

A preliminary quantitative and qualitative analysis of the collagen component of the bovine luteal extracellular matrix is reported. The amount of collagen present in corpora lutea from four stages of luteal development was estimated from measurements of hydroxyproline. The tissue content of ascorbic acid, a cofactor in collagen biosynthesis, was also determined. Extracts of luteal tissue were subjected to polyacrylamide gel electrophoresis and compared with patterns derived from standard preparations of commonly occurring collagens. Measurements of hydroxyproline showed that collagen contributed up to about one-sixth of the luteal dry matter (3% of wet weight), with the highest absolute amounts occurring in mature tissue. Ascorbic acid was present in tissue from all stages of the luteal phase, with the highest concentrations occurring in the midluteal phase. Hydroxyproline content was closely correlated with tissue weight and ascorbic acid content during the first stage of the luteal phase, indicating that collagen is produced as a component of tissue growth, supported by the concurrent accumulation of its biosynthetic cofactor. The highest concentrations of hydroxyproline occurred in the final stage of the luteal phase, suggesting that luteolysis is associated with a preferential loss of cellular rather than extracellular material. From the electrophoretic analysis, the fibrillar collagen type I could be identified at all stages of the luteal phase. We conclude that collagen is a major component of the luteal extracellular matrix and is produced as an integral component of tissue development. The presence of a fibrillar rather than a basement membrane type of collagen suggests a significant change in gene expression when follicular tissue is remodelled into that of the corpus luteum.