Localization and interaction of hyaluronic acid and inter-alpha-trypsin inhibitor in stimulated preovulatory rat ovaries

Proteins of the inter-alpha-trypsin inhibitor (/alpha/) family are reported to stabilize the expanding cumulus extracellular matrix by direct binding with hyaluronic acid in mouse. The aim of this study is to compare the expr ession and distribution of hyaluronic acid and /alpha/ in the rat ovaries d uring gonadotropin-induced follicle development. Immuno- and affinity histo chemical staining was performed in rat ovary using a polyclonal antibody ra ised against purified human /alpha/ and a hyaluronic acid-specific probe (b iotinylated hyaluronic acid-binding protein). During a preovulatory stage, relatively large amounts of hyaluronic acid were present in the follicular fluid as well as on the surface of expanding cumulus cells and theca/stroma l cells. The area of /alpha/ reactivity in stimulated preovulatory follicle s was almost the same as that of diffuse deposition of hyaluronic acid. In an in vivo rat model, inhibition of hyaluronic acid synthesis resulted in i nhibition of cumulus oocyte complex (COC) expansion accompanied by reduced staining for /alpha/ and hyaluronic acid. Western blot analysis of /alpha/ and immunoassay for hyaluronic acid in tissue extracts from hCG-stimulated ovaries indicated marked increase in /alpha/ and hyaluronic acid expression . These findings support the hypothesis that the co-distribution of /alpha/ and hyaluronic acid may serve to organize the formation of the cumulus ext racellular matrix in the rat ovary.