Previously we reported that the 55-kDa fertility-associated protein in Hols
tein bull seminal plasma (SP) is osteopontin (OPN). The objective of the pr
esent study was to localize OPN in tissues and fluids in the Holstein hull
reproductive tract to determine its origin. Antisera generated against huma
n recombinant OPN, as well as antiserum prepared against purified bovine se
minal plasma OPN, reacted with protein in SP, accessory sex gland fluid, se
minal vesicle fluid, ampullary fluid, and urine using one- and two-dimensio
nal SDS-PACE Western blot analysis. However, these antisera failed to detec
t OPN in cauda epididymal fluid or solubilized sperm membranes. Immunofluor
escence histochemistry localized OPN in the lumen and epithelial cells of t
he seminal vesicle and ampulla, but not in tissues of testis, epididymis, p
rostate, and bulbourethral gland. OPN was not detected immunohistochemicall
y in epididymal, ampullary, or ejaculated sperm treated with or without Tri
ton X-100. We concluded that the primary sources of OPN in bull SP are the
seminal vesicles and ampulla.